update to 5.0.1, part one (map binder, assisted inject, error messages)

gradle.properties

@@ -1,6 +1,6 @@
 group = org.xbib
 name = guice
-version = 4.4.2.0
+version = 5.0.1.0
 
 org.gradle.warning.mode = ALL
 gradle.wrapper.version = 6.6.1
@@ -8,5 +8,5 @@ javax-inject.version = 1
 guava.version = 30.1
 # test
 junit.version = 5.7.2
-junit4.version = 4.13
+junit4.version = 4.13.2
 log4j.version = 2.14.1

src/main/java/com/google/inject/Key.java

@@ -1,24 +1,20 @@
 package com.google.inject;
 
-import com.google.common.base.Supplier;
-import com.google.common.base.Suppliers;
-import com.google.inject.internal.Annotations;
-import com.google.inject.internal.MoreTypes;
-
-import java.lang.annotation.Annotation;
-import java.lang.reflect.Type;
-
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.inject.internal.Annotations.generateAnnotation;
 import static com.google.inject.internal.Annotations.isAllDefaultMethods;
 
+import com.google.inject.internal.Annotations;
+import com.google.inject.internal.MoreTypes;
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+
 /**
- * Binding key consisting of an injection type and an optional annotation.
+ * Guice uses Key objects to identify a dependency that can be resolved by the Guice {@link
- * Matches the type and annotation at a point of injection.
+ * Injector}. A Guice key consists of an injection type and an optional annotation.
  *
- * <p>For example, {@code Key.get(Service.class, Transactional.class)} will
+ * <p>For example, {@code Key.get(Service.class, Transactional.class)} will match:
- * match:
  *
  * <pre>
  *   {@literal @}Inject
@@ -27,21 +23,20 @@ import static com.google.inject.internal.Annotations.isAllDefaultMethods;
  *   }
  * </pre>
  *
- * <p>{@code Key} supports generic types via subclassing just like {@link
+ * <p>{@code Key} supports generic types via subclassing just like {@link TypeLiteral}.
- * TypeLiteral}.
  *
- * <p>Keys do not differentiate between primitive types (int, char, etc.) and
+ * <p>Keys do not differentiate between primitive types (int, char, etc.) and their corresponding
- * their corresponding wrapper types (Integer, Character, etc.). Primitive
+ * wrapper types (Integer, Character, etc.). Primitive types will be replaced with their wrapper
- * types will be replaced with their wrapper types when keys are created.
+ * types when keys are created.
+ *
+ * @author crazybob@google.com (Bob Lee)
  */
 public class Key<T> {
 
     private final AnnotationStrategy annotationStrategy;
 
     private final TypeLiteral<T> typeLiteral;
-
     private final int hashCode;
-
     // This field is updated using the 'Data-Race-Ful' lazy intialization pattern
     // See http://jeremymanson.blogspot.com/2008/12/benign-data-races-in-java.html for a detailed
     // explanation.
@@ -50,19 +45,18 @@ public class Key<T> {
     /**
      * Constructs a new key. Derives the type from this class's type parameter.
      *
-     * <p>Clients create an empty anonymous subclass. Doing so embeds the type
+     * <p>Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
-     * parameter in the anonymous class's type hierarchy so we can reconstitute it
+     * anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
-     * at runtime despite erasure.
      *
-     * <p>Example usage for a binding of type {@code Foo} annotated with
+     * <p>Example usage for a binding of type {@code Foo} annotated with {@code @Bar}:
-     * {@code @Bar}:
      *
      * <p>{@code new Key<Foo>(Bar.class) {}}.
      */
     @SuppressWarnings("unchecked")
     protected Key(Class<? extends Annotation> annotationType) {
         this.annotationStrategy = strategyFor(annotationType);
-        this.typeLiteral = MoreTypes.canonicalizeForKey(
+        this.typeLiteral =
+                MoreTypes.canonicalizeForKey(
                         (TypeLiteral<T>) TypeLiteral.fromSuperclassTypeParameter(getClass()));
         this.hashCode = computeHashCode();
     }
@@ -70,12 +64,10 @@ public class Key<T> {
     /**
      * Constructs a new key. Derives the type from this class's type parameter.
      *
-     * <p>Clients create an empty anonymous subclass. Doing so embeds the type
+     * <p>Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
-     * parameter in the anonymous class's type hierarchy so we can reconstitute it
+     * anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
-     * at runtime despite erasure.
      *
-     * <p>Example usage for a binding of type {@code Foo} annotated with
+     * <p>Example usage for a binding of type {@code Foo} annotated with {@code @Bar}:
-     * {@code @Bar}:
      *
      * <p>{@code new Key<Foo>(new Bar()) {}}.
      */
@@ -83,7 +75,8 @@ public class Key<T> {
     protected Key(Annotation annotation) {
         // no usages, not test-covered
         this.annotationStrategy = strategyFor(annotation);
-        this.typeLiteral = MoreTypes.canonicalizeForKey(
+        this.typeLiteral =
+                MoreTypes.canonicalizeForKey(
                         (TypeLiteral<T>) TypeLiteral.fromSuperclassTypeParameter(getClass()));
         this.hashCode = computeHashCode();
     }
@@ -91,9 +84,8 @@ public class Key<T> {
     /**
      * Constructs a new key. Derives the type from this class's type parameter.
      *
-     * <p>Clients create an empty anonymous subclass. Doing so embeds the type
+     * <p>Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
-     * parameter in the anonymous class's type hierarchy so we can reconstitute it
+     * anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
-     * at runtime despite erasure.
      *
      * <p>Example usage for a binding of type {@code Foo}:
      *
@@ -102,14 +94,13 @@ public class Key<T> {
     @SuppressWarnings("unchecked")
     protected Key() {
         this.annotationStrategy = NullAnnotationStrategy.INSTANCE;
-        this.typeLiteral = MoreTypes.canonicalizeForKey(
+        this.typeLiteral =
+                MoreTypes.canonicalizeForKey(
                         (TypeLiteral<T>) TypeLiteral.fromSuperclassTypeParameter(getClass()));
         this.hashCode = computeHashCode();
     }
 
-    /**
+    /** Unsafe. Constructs a key from a manually specified type. */
-     * Unsafe. Constructs a key from a manually specified type.
-     */
     @SuppressWarnings("unchecked")
     private Key(Type type, AnnotationStrategy annotationStrategy) {
         this.annotationStrategy = annotationStrategy;
@@ -117,154 +108,37 @@ public class Key<T> {
         this.hashCode = computeHashCode();
     }
 
-    /**
+    /** Constructs a key from a manually specified type. */
-     * Constructs a key from a manually specified type.
-     */
     private Key(TypeLiteral<T> typeLiteral, AnnotationStrategy annotationStrategy) {
         this.annotationStrategy = annotationStrategy;
         this.typeLiteral = MoreTypes.canonicalizeForKey(typeLiteral);
         this.hashCode = computeHashCode();
     }
 
-    /**
+    /** Computes the hash code for this key. */
-     * Gets a key for an injection type and an annotation strategy.
-     */
-    static <T> Key<T> get(Class<T> type, AnnotationStrategy annotationStrategy) {
-        return new Key<T>(type, annotationStrategy);
-    }
-
-    /**
-     * Gets a key for an injection type.
-     */
-    public static <T> Key<T> get(Class<T> type) {
-        return new Key<T>(type, NullAnnotationStrategy.INSTANCE);
-    }
-
-    /**
-     * Gets a key for an injection type and an annotation type.
-     */
-    public static <T> Key<T> get(Class<T> type, Class<? extends Annotation> annotationType) {
-        return new Key<T>(type, strategyFor(annotationType));
-    }
-
-    /**
-     * Gets a key for an injection type and an annotation.
-     */
-    public static <T> Key<T> get(Class<T> type, Annotation annotation) {
-        return new Key<T>(type, strategyFor(annotation));
-    }
-
-    /**
-     * Gets a key for an injection type.
-     */
-    public static Key<?> get(Type type) {
-        return new Key<Object>(type, NullAnnotationStrategy.INSTANCE);
-    }
-
-    /**
-     * Gets a key for an injection type and an annotation type.
-     */
-    public static Key<?> get(Type type, Class<? extends Annotation> annotationType) {
-        return new Key<Object>(type, strategyFor(annotationType));
-    }
-
-    /**
-     * Gets a key for an injection type and an annotation.
-     */
-    public static Key<?> get(Type type, Annotation annotation) {
-        return new Key<Object>(type, strategyFor(annotation));
-    }
-
-    /**
-     * Gets a key for an injection type.
-     */
-    public static <T> Key<T> get(TypeLiteral<T> typeLiteral) {
-        return new Key<T>(typeLiteral, NullAnnotationStrategy.INSTANCE);
-    }
-
-    /**
-     * Gets a key for an injection type and an annotation type.
-     */
-    public static <T> Key<T> get(TypeLiteral<T> typeLiteral, Class<? extends Annotation> annotationType) {
-        return new Key<T>(typeLiteral, strategyFor(annotationType));
-    }
-
-    /**
-     * Gets a key for an injection type and an annotation.
-     */
-    public static <T> Key<T> get(TypeLiteral<T> typeLiteral, Annotation annotation) {
-        return new Key<T>(typeLiteral, strategyFor(annotation));
-    }
-
-    /**
-     * Gets the strategy for an annotation.
-     */
-    static AnnotationStrategy strategyFor(Annotation annotation) {
-        checkNotNull(annotation, "annotation");
-        Class<? extends Annotation> annotationType = annotation.annotationType();
-        ensureRetainedAtRuntime(annotationType);
-        ensureIsBindingAnnotation(annotationType);
-
-        if (Annotations.isMarker(annotationType)) {
-            return new AnnotationTypeStrategy(annotationType, annotation);
-        }
-
-        return new AnnotationInstanceStrategy(Annotations.canonicalizeIfNamed(annotation));
-    }
-
-    /**
-     * Gets the strategy for an annotation type.
-     */
-    static AnnotationStrategy strategyFor(Class<? extends Annotation> annotationType) {
-        annotationType = Annotations.canonicalizeIfNamed(annotationType);
-        if (isAllDefaultMethods(annotationType)) {
-            return strategyFor(generateAnnotation(annotationType));
-        }
-
-        checkNotNull(annotationType, "annotation type");
-        ensureRetainedAtRuntime(annotationType);
-        ensureIsBindingAnnotation(annotationType);
-        return new AnnotationTypeStrategy(annotationType, null);
-
-    }
-
-    private static void ensureRetainedAtRuntime(
-            Class<? extends Annotation> annotationType) {
-        checkArgument(Annotations.isRetainedAtRuntime(annotationType),
-                "%s is not retained at runtime. Please annotate it with @Retention(RUNTIME).",
-                annotationType.getName());
-    }
-
-    private static void ensureIsBindingAnnotation(Class<? extends Annotation> annotationType) {
-        checkArgument(Annotations.isBindingAnnotation(annotationType),
-                "%s is not a binding annotation. Please annotate it with @BindingAnnotation.",
-                annotationType.getName());
-    }
-
-    /**
-     * Computes the hash code for this key.
-     */
     private int computeHashCode() {
         return typeLiteral.hashCode() * 31 + annotationStrategy.hashCode();
     }
 
-    /**
+    /** Gets the key type. */
-     * Gets the key type.
-     */
     public final TypeLiteral<T> getTypeLiteral() {
         return typeLiteral;
     }
 
-    /**
+    /** Gets the annotation type. Will be {@code null} if this key lacks an annotation. */
-     * Gets the annotation type.
-     */
     public final Class<? extends Annotation> getAnnotationType() {
         return annotationStrategy.getAnnotationType();
     }
 
     /**
-     * Gets the annotation.
+     * Gets the annotation instance if available. Will be {@code null} if this key lacks an annotation
+     * <i>or</i> the key was constructed with a {@code Class<Annotation>}.
+     *
+     * <p><b>Warning:</b> this can return null even if this key is annotated. To check whether a
+     * {@code Key} has an annotation use {@link #hasAnnotationType} instead.
      */
+    // TODO(diamondm) consider deprecating this in favor of a method that ISEs if hasAnnotationType()
+    // is true but this would return null.
     public final Annotation getAnnotation() {
         return annotationStrategy.getAnnotation();
     }
@@ -287,9 +161,7 @@ public class Key<T> {
         return typeLiteral.getRawType();
     }
 
-    /**
+    /** Gets the key of this key's provider. */
-     * Gets the key of this key's provider.
-     */
     Key<Provider<T>> providerKey() {
         return ofType(typeLiteral.providerType());
     }
@@ -324,46 +196,178 @@ public class Key<T> {
         return local;
     }
 
-    /**
+    /** Gets a key for an injection type and an annotation strategy. */
-     * Returns a new key of the specified type with the same annotation as this
+    static <T> Key<T> get(Class<T> type, AnnotationStrategy annotationStrategy) {
-     * key.
-     */
-    public <T> Key<T> ofType(Class<T> type) {
         return new Key<T>(type, annotationStrategy);
     }
 
+    /** Gets a key for an injection type. */
+    public static <T> Key<T> get(Class<T> type) {
+        return new Key<T>(type, NullAnnotationStrategy.INSTANCE);
+    }
+
+    /** Gets a key for an injection type and an annotation type. */
+    public static <T> Key<T> get(Class<T> type, Class<? extends Annotation> annotationType) {
+        return new Key<T>(type, strategyFor(annotationType));
+    }
+
+    /** Gets a key for an injection type and an annotation. */
+    public static <T> Key<T> get(Class<T> type, Annotation annotation) {
+        return new Key<T>(type, strategyFor(annotation));
+    }
+
+    /** Gets a key for an injection type. */
+    public static Key<?> get(Type type) {
+        return new Key<>(type, NullAnnotationStrategy.INSTANCE);
+    }
+
+    /** Gets a key for an injection type and an annotation type. */
+    public static Key<?> get(Type type, Class<? extends Annotation> annotationType) {
+        return new Key<>(type, strategyFor(annotationType));
+    }
+
+    /** Gets a key for an injection type and an annotation. */
+    public static Key<?> get(Type type, Annotation annotation) {
+        return new Key<>(type, strategyFor(annotation));
+    }
+
+    /** Gets a key for an injection type. */
+    public static <T> Key<T> get(TypeLiteral<T> typeLiteral) {
+        return new Key<T>(typeLiteral, NullAnnotationStrategy.INSTANCE);
+    }
+
+    /** Gets a key for an injection type and an annotation type. */
+    public static <T> Key<T> get(
+            TypeLiteral<T> typeLiteral, Class<? extends Annotation> annotationType) {
+        return new Key<T>(typeLiteral, strategyFor(annotationType));
+    }
+
+    /** Gets a key for an injection type and an annotation. */
+    public static <T> Key<T> get(TypeLiteral<T> typeLiteral, Annotation annotation) {
+        return new Key<T>(typeLiteral, strategyFor(annotation));
+    }
+
     /**
-     * Returns a new key of the specified type with the same annotation as this
+     * Returns a new key of the specified type with the same annotation as this key.
-     * key.
+     *
+     * @since 3.0
+     */
+    public <U> Key<U> ofType(Class<U> type) {
+        return new Key<>(type, annotationStrategy);
+    }
+
+    /**
+     * Returns a new key of the specified type with the same annotation as this key.
+     *
+     * @since 3.0
      */
     public Key<?> ofType(Type type) {
-        return new Key<Object>(type, annotationStrategy);
+        return new Key<>(type, annotationStrategy);
     }
 
     /**
-     * Returns a new key of the specified type with the same annotation as this
+     * Returns a new key of the specified type with the same annotation as this key.
-     * key.
+     *
+     * @since 3.0
      */
-    public <T> Key<T> ofType(TypeLiteral<T> type) {
+    public <U> Key<U> ofType(TypeLiteral<U> type) {
-        return new Key<T>(type, annotationStrategy);
+        return new Key<U>(type, annotationStrategy);
+    }
+
+    /**
+     * Returns a new key of the same type with the specified annotation.
+     *
+     * <p>This is equivalent to {@code Key.get(key.getTypeLiteral(), annotation)} but may be more
+     * convenient to use in certain cases.
+     *
+     * @since 5.0
+     */
+    public Key<T> withAnnotation(Class<? extends Annotation> annotationType) {
+        return new Key<T>(typeLiteral, strategyFor(annotationType));
+    }
+
+    /**
+     * Returns a new key of the same type with the specified annotation.
+     *
+     * <p>This is equivalent to {@code Key.get(key.getTypeLiteral(), annotation)} but may be more
+     * convenient to use in certain cases.
+     *
+     * @since 5.0
+     */
+    public Key<T> withAnnotation(Annotation annotation) {
+        return new Key<T>(typeLiteral, strategyFor(annotation));
     }
 
     /**
      * Returns true if this key has annotation attributes.
+     *
+     * @since 3.0
      */
     public boolean hasAttributes() {
         return annotationStrategy.hasAttributes();
     }
 
     /**
-     * Returns this key without annotation attributes, i.e. with only the
+     * Returns this key without annotation attributes, i.e. with only the annotation type.
-     * annotation type.
+     *
+     * @since 3.0
      */
     public Key<T> withoutAttributes() {
         return new Key<T>(typeLiteral, annotationStrategy.withoutAttributes());
     }
 
-    enum NullAnnotationStrategy implements AnnotationStrategy {
+    interface AnnotationStrategy {
+        Annotation getAnnotation();
+
+        Class<? extends Annotation> getAnnotationType();
+
+        boolean hasAttributes();
+
+        AnnotationStrategy withoutAttributes();
+    }
+
+    /** Gets the strategy for an annotation. */
+    static AnnotationStrategy strategyFor(Annotation annotation) {
+        checkNotNull(annotation, "annotation");
+        Class<? extends Annotation> annotationType = annotation.annotationType();
+        ensureRetainedAtRuntime(annotationType);
+        ensureIsBindingAnnotation(annotationType);
+
+        if (Annotations.isMarker(annotationType)) {
+            return new AnnotationTypeStrategy(annotationType, annotation);
+        }
+
+        return new AnnotationInstanceStrategy(Annotations.canonicalizeIfNamed(annotation));
+    }
+
+    /** Gets the strategy for an annotation type. */
+    static AnnotationStrategy strategyFor(Class<? extends Annotation> annotationType) {
+        annotationType = Annotations.canonicalizeIfNamed(annotationType);
+        if (isAllDefaultMethods(annotationType)) {
+            return strategyFor(generateAnnotation(annotationType));
+        }
+
+        checkNotNull(annotationType, "annotation type");
+        ensureRetainedAtRuntime(annotationType);
+        ensureIsBindingAnnotation(annotationType);
+        return new AnnotationTypeStrategy(annotationType, null);
+    }
+
+    private static void ensureRetainedAtRuntime(Class<? extends Annotation> annotationType) {
+        checkArgument(
+                Annotations.isRetainedAtRuntime(annotationType),
+                "%s is not retained at runtime. Please annotate it with @Retention(RUNTIME).",
+                annotationType.getName());
+    }
+
+    private static void ensureIsBindingAnnotation(Class<? extends Annotation> annotationType) {
+        checkArgument(
+                Annotations.isBindingAnnotation(annotationType),
+                "%s is not a binding annotation. Please annotate it with @BindingAnnotation.",
+                annotationType.getName());
+    }
+
+    static enum NullAnnotationStrategy implements AnnotationStrategy {
         INSTANCE;
 
         @Override
@@ -392,17 +396,6 @@ public class Key<T> {
         }
     }
 
-    interface AnnotationStrategy {
-
-        Annotation getAnnotation();
-
-        Class<? extends Annotation> getAnnotationType();
-
-        boolean hasAttributes();
-
-        AnnotationStrategy withoutAttributes();
-    }
-
     // this class not test-covered
     static class AnnotationInstanceStrategy implements AnnotationStrategy {
 
@@ -460,8 +453,7 @@ public class Key<T> {
         // Keep the instance around if we have it so the client can request it.
         final Annotation annotation;
 
-        AnnotationTypeStrategy(Class<? extends Annotation> annotationType,
+        AnnotationTypeStrategy(Class<? extends Annotation> annotationType, Annotation annotation) {
-                               Annotation annotation) {
             this.annotationType = checkNotNull(annotationType, "annotation type");
             this.annotation = annotation;
         }

src/main/java/com/google/inject/RestrictedBindingSource.java

@@ -0,0 +1,120 @@
+package com.google.inject;
+
+import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Annotation;
+import java.lang.annotation.Documented;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation restricting the binding of the target type to permitted sources.
+ *
+ * <p>Bindings restricted by this annotation may only be created by sources annotated with a permit
+ * from {@link #permits} -- otherwise, an error message including the {@link #explanation} is
+ * issued.
+ *
+ * <p>There are two kinds of binding source:
+ *
+ * <ol>
+ *   <li>Module: a module is the source of a binding if it creates it (either directly, or
+ *       indirectly by installing another module). For example: if module A creates restricted
+ *       binding X, and module C installs module B that installs A; then all 3 modules C,B,A are
+ *       sources of X, and it's enough for any one of them to be annotated with a permit from X's
+ *       restriction.
+ *   <li>Method Scanner ({@code ModuleAnnotatedMethodScanner}): If a binding was created by a
+ *       scanner, then that scanner is also a source of the binding (in addition to the module
+ *       sources) and a permit may be given to the scanner by annotating its class.
+ * </ol>
+ *
+ * <p>Bindings with qualifier annotations are restricted solely by the annotation on their qualifier
+ * (restrictions on the type are ignored for qualified bindings). Unqualified bindings are
+ * restricted by the annotation on their type.
+ *
+ * <p>This allows libraries to prevent their clients from binding their keys, similar to how
+ * declaring a class final prevents subtyping. For example, a library may want to prevent users from
+ * creating mock bindings for tests, using the {@link #explanation} - included in the error message
+ * - to point them to a supported testing module.
+ *
+ * <p>Example usage:
+ *
+ * <pre>{@code
+ * @RestrictedBindingSource.Permit
+ * @Retention(RetentionPolicy.RUNTIME)
+ * @interface NetworkPermit {}
+ *
+ * @RestrictedBindingSource(
+ *   explanation = "Only NetworkModule can create network bindings.",
+ *   permits = {NetworkPermit.class})
+ * @Qualifier
+ * @Retention(RetentionPolicy.RUNTIME)
+ * public @interface GatewayIpAdress {}
+ *
+ * @NetworkPermit
+ * public final class NetworkModule extends AbstractModule {
+ *   @Provides
+ *   @GatewayIpAdress // Allowed because the module is annotated with @NetworkPermit.
+ *   int provideGatewayIp() { ... }
+ * }
+ * }</pre>
+ *
+ * @author vzm@google.com (Vladimir Makaric)
+ * @since 5.0
+ */
+@Inherited
+@Retention(RUNTIME)
+@Target(TYPE)
+public @interface RestrictedBindingSource {
+  /**
+   * Explanation of why binding this target type is restricted.
+   *
+   * <p>Will appear as the error message if the target type is bound by non-allowed modules.
+   */
+  String explanation();
+
+  /**
+   * Meta-annotation indicating that the target annotation is a permit for binding restricted
+   * bindings. Annotating a binding source (defined in top-level javadoc) with a permit gives it
+   * permission to bind the restricted bindings guarded by the permit (see {@link #permits}).
+   *
+   * @since 5.0
+   */
+  @Documented
+  @Retention(RUNTIME)
+  @Target(ANNOTATION_TYPE)
+  public @interface Permit {}
+
+  /**
+   * List of {@code Permit} annotations (must be non-empty), one of which has has to be present on a
+   * restricted binding's source (defined in top-level javadoc).
+   */
+  Class<? extends Annotation>[] permits();
+
+  /**
+   * Exempt modules whose fully qualified class names match this regex.
+   *
+   * <p>If any module on the binding's module stack matches this regex, the binding is allowed (no
+   * permit necessary). No module is exempt by default (empty string).
+   *
+   * <p>Inteded to be used when retrofitting a binding with this restriction. When restricting an
+   * existing binding, it's often practical to first restrict with exemptions for existing
+   * violations (to prevent new violations), before updating the code in violation to use the
+   * permitted module(s).
+   */
+  String exemptModules() default "";
+
+  /**
+   * Level of restriction. Determines how violations are handled.
+   *
+   * @since 5.0
+   */
+  public static enum RestrictionLevel {
+    WARNING,
+    ERROR;
+  }
+
+  RestrictionLevel restrictionLevel() default RestrictionLevel.ERROR;
+}

src/main/java/com/google/inject/assistedinject/FactoryModuleBuilder.java

@@ -5,14 +5,15 @@ import com.google.inject.Key;
 import com.google.inject.Module;
 import com.google.inject.Provider;
 import com.google.inject.TypeLiteral;
-
 import java.lang.annotation.Annotation;
+import java.lang.invoke.MethodHandles;
 
 /**
  * Provides a factory that combines the caller's arguments with injector-supplied values to
  * construct objects.
  *
  * <h3>Defining a factory</h3>
+ *
  * Create an interface whose methods return the constructed type, or any of its supertypes. The
  * method's parameters are the arguments required to build the constructed type.
  *
@@ -24,6 +25,7 @@ import java.lang.annotation.Annotation;
  * or <i>newPayment</i>.
  *
  * <h3>Creating a type that accepts factory parameters</h3>
+ *
  * {@code constructedType} is a concrete class with an {@literal @}{@link com.google.inject.Inject
  * Inject}-annotated constructor. In addition to injector-supplied parameters, the constructor
  * should have parameters that match each of the factory method's parameters. Each factory-supplied
@@ -42,10 +44,10 @@ import java.lang.annotation.Annotation;
  * }</pre>
  *
  * <h3>Multiple factory methods for the same type</h3>
+ *
  * If the factory contains many methods that return the same type, you can create multiple
- * constructors in your concrete class, each constructor marked with with
+ * constructors in your concrete class, each constructor marked with with {@literal @}{@link
- * {@literal @}{@link AssistedInject}, in order to match the different parameters types of the
+ * AssistedInject}, in order to match the different parameters types of the factory methods.
- * factory methods.
  *
  * <pre>public interface PaymentFactory {
  *    Payment create(Date startDate, Money amount);
@@ -72,8 +74,8 @@ import java.lang.annotation.Annotation;
  * }</pre>
  *
  * <h3>Configuring simple factories</h3>
- * In your {@link Module module}, install a {@code FactoryModuleBuilder} that creates the
+ *
- * factory:
+ * In your {@link Module module}, install a {@code FactoryModuleBuilder} that creates the factory:
  *
  * <pre>install(new FactoryModuleBuilder()
  *     .implement(Payment.class, RealPayment.class)
@@ -83,8 +85,9 @@ import java.lang.annotation.Annotation;
  * factory cannot be used until the injector has been initialized.
  *
  * <h3>Configuring complex factories</h3>
- * Factories can create an arbitrary number of objects, one per each method.  Each factory
+ *
- * method can be configured using <code>.implement</code>.
+ * Factories can create an arbitrary number of objects, one per each method. Each factory method can
+ * be configured using <code>.implement</code>.
  *
  * <pre>public interface OrderFactory {
  *    Payment create(Date startDate, Money amount);
@@ -99,12 +102,14 @@ import java.lang.annotation.Annotation;
  *     // excluding .implement for Shipment means the implementation class
  *     // will be 'Shipment' itself, which is legal if it's not an interface.
  *     .implement(Receipt.class, RealReceipt.class)
- *     .build(OrderFactory.class));
+ *     .build(OrderFactory.class));</pre>
+ *
  * </pre>
  *
  * <h3>Using the factory</h3>
- * Inject your factory into your application classes. When you use the factory, your arguments
+ *
- * will be combined with values from the injector to construct an instance.
+ * Inject your factory into your application classes. When you use the factory, your arguments will
+ * be combined with values from the injector to construct an instance.
  *
  * <pre>public class PaymentAction {
  *   {@literal @}Inject private PaymentFactory paymentFactory;
@@ -116,9 +121,10 @@ import java.lang.annotation.Annotation;
  * }</pre>
  *
  * <h3>Making parameter types distinct</h3>
- * The types of the factory method's parameters must be distinct. To use multiple parameters of
+ *
- * the same type, use a named {@literal @}{@link Assisted} annotation to disambiguate the
+ * The types of the factory method's parameters must be distinct. To use multiple parameters of the
- * parameters. The names must be applied to the factory method's parameters:
+ * same type, use a named {@literal @}{@link Assisted} annotation to disambiguate the parameters.
+ * The names must be applied to the factory method's parameters:
  *
  * <pre>public interface PaymentFactory {
  *   Payment create(
@@ -142,14 +148,17 @@ import java.lang.annotation.Annotation;
  * }</pre>
  *
  * <h3>Values are created by Guice</h3>
+ *
  * Returned factories use child injectors to create values. The values are eligible for method
  * interception. In addition, {@literal @}{@literal Inject} members will be injected before they are
  * returned.
  *
  * <h3>More configuration options</h3>
+ *
  * In addition to simply specifying an implementation class for any returned type, factories' return
  * values can be automatic or can be configured to use annotations:
- * If you just want to return the types specified in the factory, do not configure any
+ *
+ * <p>If you just want to return the types specified in the factory, do not configure any
  * implementations:
  *
  * <pre>public interface FruitFactory {
@@ -161,7 +170,8 @@ import java.lang.annotation.Annotation;
  * }</pre>
  *
  * Note that any type returned by the factory in this manner needs to be an implementation class.
- * To return two different implementations for the same interface from your factory, use binding
+ *
+ * <p>To return two different implementations for the same interface from your factory, use binding
  * annotations on your return types:
  *
  * <pre>interface CarFactory {
@@ -177,142 +187,138 @@ import java.lang.annotation.Annotation;
  * }</pre>
  *
  * <h3>Implementation limitations</h3>
- * As a limitation of the implementation, it is prohibited to declare a factory method that
+ *
- * accepts a {@code Provider} as one of its arguments.
+ * As a limitation of the implementation, it is prohibited to declare a factory method that accepts
+ * a {@code Provider} as one of its arguments.
+ *
+ * @since 3.0
+ * @author schmitt@google.com (Peter Schmitt)
  */
 public final class FactoryModuleBuilder {
 
     private final BindingCollector bindings = new BindingCollector();
+    private MethodHandles.Lookup lookups;
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
-     */
     public <T> FactoryModuleBuilder implement(Class<T> source, Class<? extends T> target) {
         return implement(source, TypeLiteral.get(target));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
-     */
     public <T> FactoryModuleBuilder implement(Class<T> source, TypeLiteral<? extends T> target) {
         return implement(TypeLiteral.get(source), target);
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
-     */
     public <T> FactoryModuleBuilder implement(TypeLiteral<T> source, Class<? extends T> target) {
         return implement(source, TypeLiteral.get(target));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            TypeLiteral<T> source, TypeLiteral<? extends T> target) {
-    public <T> FactoryModuleBuilder implement(TypeLiteral<T> source,
-                                              TypeLiteral<? extends T> target) {
         return implement(Key.get(source), target);
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            Class<T> source, Annotation annotation, Class<? extends T> target) {
-    public <T> FactoryModuleBuilder implement(Class<T> source, Annotation annotation,
-                                              Class<? extends T> target) {
         return implement(source, annotation, TypeLiteral.get(target));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            Class<T> source, Annotation annotation, TypeLiteral<? extends T> target) {
-    public <T> FactoryModuleBuilder implement(Class<T> source, Annotation annotation,
-                                              TypeLiteral<? extends T> target) {
         return implement(TypeLiteral.get(source), annotation, target);
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            TypeLiteral<T> source, Annotation annotation, Class<? extends T> target) {
-    public <T> FactoryModuleBuilder implement(TypeLiteral<T> source, Annotation annotation,
-                                              Class<? extends T> target) {
         return implement(source, annotation, TypeLiteral.get(target));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            TypeLiteral<T> source, Annotation annotation, TypeLiteral<? extends T> target) {
-    public <T> FactoryModuleBuilder implement(TypeLiteral<T> source, Annotation annotation,
-                                              TypeLiteral<? extends T> target) {
         return implement(Key.get(source, annotation), target);
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            Class<T> source, Class<? extends Annotation> annotationType, Class<? extends T> target) {
-    public <T> FactoryModuleBuilder implement(Class<T> source,
-                                              Class<? extends Annotation> annotationType, Class<? extends T> target) {
         return implement(source, annotationType, TypeLiteral.get(target));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            Class<T> source,
-    public <T> FactoryModuleBuilder implement(Class<T> source,
+            Class<? extends Annotation> annotationType,
-                                              Class<? extends Annotation> annotationType, TypeLiteral<? extends T> target) {
+            TypeLiteral<? extends T> target) {
         return implement(TypeLiteral.get(source), annotationType, target);
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            TypeLiteral<T> source,
-    public <T> FactoryModuleBuilder implement(TypeLiteral<T> source,
+            Class<? extends Annotation> annotationType,
-                                              Class<? extends Annotation> annotationType, Class<? extends T> target) {
+            Class<? extends T> target) {
         return implement(source, annotationType, TypeLiteral.get(target));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+    public <T> FactoryModuleBuilder implement(
-     */
+            TypeLiteral<T> source,
-    public <T> FactoryModuleBuilder implement(TypeLiteral<T> source,
+            Class<? extends Annotation> annotationType,
-                                              Class<? extends Annotation> annotationType, TypeLiteral<? extends T> target) {
+            TypeLiteral<? extends T> target) {
         return implement(Key.get(source, annotationType), target);
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
-     */
     public <T> FactoryModuleBuilder implement(Key<T> source, Class<? extends T> target) {
         return implement(source, TypeLiteral.get(target));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
-     */
     public <T> FactoryModuleBuilder implement(Key<T> source, TypeLiteral<? extends T> target) {
         bindings.addBinding(source, target);
         return this;
     }
 
     /**
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
+     * Typically called via {@code withLookups(MethodHandles.lookup())}. Sets the MethodHandles.Lookup
+     * that the factory implementation will use to call default methods on the factory interface.
+     * While this is not always required, it is always OK to set it. It is required if the factory
+     * passed to {@link #build} is non-public and javac generated default methods while compiling it
+     * (which javac can sometimes do if the factory uses generic types).
+     *
+     * <p>Guice will try to work properly even if this method is not called (or called with a lookups
+     * that doesn't have access to the factory), but doing so requires reflection into the JDK, which
+     * may break at any time (and trigger unsafe access warnings).
+     *
+     * @since 5.0
      */
+    public <T> FactoryModuleBuilder withLookups(MethodHandles.Lookup lookups) {
+        this.lookups = lookups;
+        return this;
+    }
+
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
     public <F> Module build(Class<F> factoryInterface) {
         return build(TypeLiteral.get(factoryInterface));
     }
 
-    /**
+    /** See the factory configuration examples at {@link FactoryModuleBuilder}. */
-     * See the factory configuration examples at {@link FactoryModuleBuilder}.
-     */
     public <F> Module build(TypeLiteral<F> factoryInterface) {
         return build(Key.get(factoryInterface));
     }
 
-
     public <F> Module build(final Key<F> factoryInterface) {
         return new AbstractModule() {
             @Override
             protected void configure() {
-                Provider<F> provider = new FactoryProvider2<F>(factoryInterface, bindings);
+                Provider<F> provider = new FactoryProvider2<>(factoryInterface, bindings, lookups);
-                bind(factoryInterface).toProvider(provider);
+                binder().skipSources(this.getClass()).bind(factoryInterface).toProvider(provider);
             }
         };
     }

src/main/java/com/google/inject/assistedinject/FactoryProvider.java

@@ -1,5 +1,7 @@
 package com.google.inject.assistedinject;
 
+import static com.google.inject.internal.Annotations.getKey;
+
 import com.google.common.base.Objects;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
@@ -13,11 +15,9 @@ import com.google.inject.Provider;
 import com.google.inject.TypeLiteral;
 import com.google.inject.internal.Errors;
 import com.google.inject.internal.ErrorsException;
-import com.google.inject.internal.Messages;
 import com.google.inject.spi.Dependency;
 import com.google.inject.spi.HasDependencies;
 import com.google.inject.spi.Message;
-
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationHandler;
@@ -28,8 +28,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import static com.google.inject.internal.Annotations.getKey;
-
 /**
  * <strong>Obsolete.</strong> Prefer {@link FactoryModuleBuilder} for its more concise API and
  * additional capability.
@@ -38,20 +36,25 @@ import static com.google.inject.internal.Annotations.getKey;
  * construct objects.
  *
  * <h3>Defining a factory</h3>
+ *
  * Create an interface whose methods return the constructed type, or any of its supertypes. The
  * method's parameters are the arguments required to build the constructed type.
+ *
  * <pre>public interface PaymentFactory {
  *   Payment create(Date startDate, Money amount);
  * }</pre>
+ *
  * You can name your factory methods whatever you like, such as <i>create</i>, <i>createPayment</i>
  * or <i>newPayment</i>.
  *
  * <h3>Creating a type that accepts factory parameters</h3>
+ *
  * {@code constructedType} is a concrete class with an {@literal @}{@link Inject}-annotated
- * constructor. In addition to injector-supplied parameters, the constructor should have
+ * constructor. In addition to injector-supplied parameters, the constructor should have parameters
- * parameters that match each of the factory method's parameters. Each factory-supplied parameter
+ * that match each of the factory method's parameters. Each factory-supplied parameter requires an
- * requires an {@literal @}{@link Assisted} annotation. This serves to document that the parameter
+ * {@literal @}{@link Assisted} annotation. This serves to document that the parameter is not bound
- * is not bound by your application's modules.
+ * by your application's modules.
+ *
  * <pre>public class RealPayment implements Payment {
  *   {@literal @}Inject
  *   public RealPayment(
@@ -62,19 +65,25 @@ import static com.google.inject.internal.Annotations.getKey;
  *     ...
  *   }
  * }</pre>
+ *
  * Any parameter that permits a null value should also be annotated {@code @Nullable}.
  *
  * <h3>Configuring factories</h3>
+ *
  * In your {@link com.google.inject.Module module}, bind the factory interface to the returned
  * factory:
+ *
  * <pre>bind(PaymentFactory.class).toProvider(
  *     FactoryProvider.newFactory(PaymentFactory.class, RealPayment.class));</pre>
+ *
  * As a side-effect of this binding, Guice will inject the factory to initialize it for use. The
  * factory cannot be used until the injector has been initialized.
  *
  * <h3>Using the factory</h3>
- * Inject your factory into your application classes. When you use the factory, your arguments
+ *
- * will be combined with values from the injector to construct an instance.
+ * Inject your factory into your application classes. When you use the factory, your arguments will
+ * be combined with values from the injector to construct an instance.
+ *
  * <pre>public class PaymentAction {
  *   {@literal @}Inject private PaymentFactory paymentFactory;
  *
@@ -85,9 +94,10 @@ import static com.google.inject.internal.Annotations.getKey;
  * }</pre>
  *
  * <h3>Making parameter types distinct</h3>
- * The types of the factory method's parameters must be distinct. To use multiple parameters of
+ *
- * the same type, use a named {@literal @}{@link Assisted} annotation to disambiguate the
+ * The types of the factory method's parameters must be distinct. To use multiple parameters of the
- * parameters. The names must be applied to the factory method's parameters:
+ * same type, use a named {@literal @}{@link Assisted} annotation to disambiguate the parameters.
+ * The names must be applied to the factory method's parameters:
  *
  * <pre>public interface PaymentFactory {
  *   Payment create(
@@ -95,7 +105,9 @@ import static com.google.inject.internal.Annotations.getKey;
  *       <strong>{@literal @}Assisted("dueDate")</strong> Date dueDate,
  *       Money amount);
  * } </pre>
+ *
  * ...and to the concrete type's constructor parameters:
+ *
  * <pre>public class RealPayment implements Payment {
  *   {@literal @}Inject
  *   public RealPayment(
@@ -109,23 +121,27 @@ import static com.google.inject.internal.Annotations.getKey;
  * }</pre>
  *
  * <h3>Values are created by Guice</h3>
+ *
  * Returned factories use child injectors to create values. The values are eligible for method
  * interception. In addition, {@literal @}{@literal Inject} members will be injected before they are
  * returned.
  *
  * <h3>Backwards compatibility using {@literal @}AssistedInject</h3>
+ *
  * Instead of the {@literal @}Inject annotation, you may annotate the constructed classes with
  * {@literal @}{@link AssistedInject}. This triggers a limited backwards-compatability mode.
  *
  * <p>Instead of matching factory method arguments to constructor parameters using their names, the
- * <strong>parameters are matched by their order</strong>. The first factory method argument is
+ * <strong>parameters are matched by their order</strong>. The first factory method argument is used
- * used for the first {@literal @}Assisted constructor parameter, etc.. Annotation names have no
+ * for the first {@literal @}Assisted constructor parameter, etc.. Annotation names have no effect.
- * effect.
  *
  * <p>Returned values are <strong>not created by Guice</strong>. These types are not eligible for
  * method interception. They do receive post-construction member injection.
  *
  * @param <F> The factory interface
+ * @author jmourits@google.com (Jerome Mourits)
+ * @author jessewilson@google.com (Jesse Wilson)
+ * @author dtm@google.com (Daniel Martin)
  * @deprecated use {@link FactoryModuleBuilder} instead.
  */
 @Deprecated
@@ -136,19 +152,11 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
      * to factory methods. The new child injector implementation lives in FactoryProvider2.
      */
 
+    private Injector injector;
+
     private final TypeLiteral<F> factoryType;
     private final TypeLiteral<?> implementationType;
     private final Map<Method, AssistedConstructor<?>> factoryMethodToConstructor;
-    private Injector injector;
-
-    private FactoryProvider(TypeLiteral<F> factoryType,
-                            TypeLiteral<?> implementationType,
-                            Map<Method, AssistedConstructor<?>> factoryMethodToConstructor) {
-        this.factoryType = factoryType;
-        this.implementationType = implementationType;
-        this.factoryMethodToConstructor = factoryMethodToConstructor;
-        checkDeclaredExceptionsMatch();
-    }
 
     public static <F> Provider<F> newFactory(Class<F> factoryType, Class<?> implementationType) {
         return newFactory(TypeLiteral.get(factoryType), TypeLiteral.get(implementationType));
@@ -156,8 +164,8 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
 
     public static <F> Provider<F> newFactory(
             TypeLiteral<F> factoryType, TypeLiteral<?> implementationType) {
-        Map<Method, AssistedConstructor<?>> factoryMethodToConstructor
+        Map<Method, AssistedConstructor<?>> factoryMethodToConstructor =
-                = createMethodMapping(factoryType, implementationType);
+                createMethodMapping(factoryType, implementationType);
 
         if (!factoryMethodToConstructor.isEmpty()) {
             return new FactoryProvider<F>(factoryType, implementationType, factoryMethodToConstructor);
@@ -171,8 +179,8 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
 
             try {
                 for (Method method : factoryType.getRawType().getMethods()) {
-                    Key<?> returnType = getKey(factoryType.getReturnType(method), method,
+                    Key<?> returnType =
-                            method.getAnnotations(), errors);
+                            getKey(factoryType.getReturnType(method), method, method.getAnnotations(), errors);
                     if (!implementationKey.equals(returnType)) {
                         collector.addBinding(returnType, implementationType);
                     }
@@ -181,83 +189,18 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
                 throw new ConfigurationException(e.getErrors().getMessages());
             }
 
-            return new FactoryProvider2<F>(Key.get(factoryType), collector);
+            return new FactoryProvider2<F>(Key.get(factoryType), collector, /* userLookups= */ null);
         }
     }
 
-    private static Map<Method, AssistedConstructor<?>> createMethodMapping(
+    private FactoryProvider(
-            TypeLiteral<?> factoryType, TypeLiteral<?> implementationType) {
+            TypeLiteral<F> factoryType,
-        List<AssistedConstructor<?>> constructors = Lists.newArrayList();
+            TypeLiteral<?> implementationType,
-
+            Map<Method, AssistedConstructor<?>> factoryMethodToConstructor) {
-        for (Constructor<?> constructor : implementationType.getRawType().getDeclaredConstructors()) {
+        this.factoryType = factoryType;
-            if (constructor.isAnnotationPresent(AssistedInject.class)) {
+        this.implementationType = implementationType;
-                AssistedConstructor<?> assistedConstructor = AssistedConstructor.create(
+        this.factoryMethodToConstructor = factoryMethodToConstructor;
-                        constructor, implementationType.getParameterTypes(constructor));
+        checkDeclaredExceptionsMatch();
-                constructors.add(assistedConstructor);
-            }
-        }
-
-        if (constructors.isEmpty()) {
-            return ImmutableMap.of();
-        }
-
-        Method[] factoryMethods = factoryType.getRawType().getMethods();
-
-        if (constructors.size() != factoryMethods.length) {
-            throw newConfigurationException("Constructor mismatch: %s has %s @AssistedInject "
-                            + "constructors, factory %s has %s creation methods", implementationType,
-                    constructors.size(), factoryType, factoryMethods.length);
-        }
-
-        Map<ParameterListKey, AssistedConstructor<?>> paramsToConstructor = Maps.newHashMap();
-
-        for (AssistedConstructor<?> c : constructors) {
-            if (paramsToConstructor.containsKey(c.getAssistedParameters())) {
-                throw new RuntimeException("Duplicate constructor, " + c);
-            }
-            paramsToConstructor.put(c.getAssistedParameters(), c);
-        }
-
-        Map<Method, AssistedConstructor<?>> result = Maps.newHashMap();
-        for (Method method : factoryMethods) {
-            if (!method.getReturnType().isAssignableFrom(implementationType.getRawType())) {
-                throw newConfigurationException("Return type of method %s is not assignable from %s",
-                        method, implementationType);
-            }
-
-            List<Type> parameterTypes = Lists.newArrayList();
-            for (TypeLiteral<?> parameterType : factoryType.getParameterTypes(method)) {
-                parameterTypes.add(parameterType.getType());
-            }
-            ParameterListKey methodParams = new ParameterListKey(parameterTypes);
-
-            if (!paramsToConstructor.containsKey(methodParams)) {
-                throw newConfigurationException("%s has no @AssistInject constructor that takes the "
-                                + "@Assisted parameters %s in that order. @AssistInject constructors are %s",
-                        implementationType, methodParams, paramsToConstructor.values());
-            }
-
-            method.getParameterAnnotations();
-            for (Annotation[] parameterAnnotations : method.getParameterAnnotations()) {
-                for (Annotation parameterAnnotation : parameterAnnotations) {
-                    if (parameterAnnotation.annotationType() == Assisted.class) {
-                        throw newConfigurationException("Factory method %s has an @Assisted parameter, which "
-                                        + "is incompatible with the deprecated @AssistedInject annotation. Please replace "
-                                        + "@AssistedInject with @Inject on the %s constructor.",
-                                method, implementationType);
-                    }
-                }
-            }
-
-            AssistedConstructor<?> matchingConstructor = paramsToConstructor.remove(methodParams);
-
-            result.put(method, matchingConstructor);
-        }
-        return result;
-    }
-
-    private static ConfigurationException newConfigurationException(String format, Object... args) {
-        return new ConfigurationException(ImmutableSet.of(new Message(Messages.format(format, args))));
     }
 
     @Inject
@@ -269,8 +212,10 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
                     // this is lame - we're not using the proper mechanism to add an
                     // error to the injector. Throughout this class we throw exceptions
                     // to add errors, which isn't really the best way in Guice
-                    throw newConfigurationException("Parameter of type '%s' is not injectable or annotated "
+                    throw newConfigurationException(
-                            + "with @Assisted for Constructor '%s'", p, c);
+                            "Parameter of type '%s' is not injectable or annotated "
+                                    + "with @Assisted for Constructor '%s'",
+                            p, c);
                 }
             }
         }
@@ -281,8 +226,10 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
             for (Class<?> constructorException : entry.getValue().getDeclaredExceptions()) {
                 if (!isConstructorExceptionCompatibleWithFactoryExeception(
                         constructorException, entry.getKey().getExceptionTypes())) {
-                    throw newConfigurationException("Constructor %s declares an exception, but no compatible "
+                    throw newConfigurationException(
-                            + "exception is thrown by the factory method %s", entry.getValue(), entry.getKey());
+                            "Constructor %s declares an exception, but no compatible "
+                                    + "exception is thrown by the factory method %s",
+                            entry.getValue(), entry.getKey());
                 }
             }
         }
@@ -302,6 +249,82 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
         return parameter.isBound(injector);
     }
 
+    private static Map<Method, AssistedConstructor<?>> createMethodMapping(
+            TypeLiteral<?> factoryType, TypeLiteral<?> implementationType) {
+        List<AssistedConstructor<?>> constructors = Lists.newArrayList();
+
+        for (Constructor<?> constructor : implementationType.getRawType().getDeclaredConstructors()) {
+            if (constructor.isAnnotationPresent(AssistedInject.class)) {
+                AssistedConstructor<?> assistedConstructor =
+                        AssistedConstructor.create(
+                                constructor, implementationType.getParameterTypes(constructor));
+                constructors.add(assistedConstructor);
+            }
+        }
+
+        if (constructors.isEmpty()) {
+            return ImmutableMap.of();
+        }
+
+        Method[] factoryMethods = factoryType.getRawType().getMethods();
+
+        if (constructors.size() != factoryMethods.length) {
+            throw newConfigurationException(
+                    "Constructor mismatch: %s has %s @AssistedInject "
+                            + "constructors, factory %s has %s creation methods",
+                    implementationType, constructors.size(), factoryType, factoryMethods.length);
+        }
+
+        Map<ParameterListKey, AssistedConstructor<?>> paramsToConstructor = Maps.newHashMap();
+
+        for (AssistedConstructor<?> c : constructors) {
+            if (paramsToConstructor.containsKey(c.getAssistedParameters())) {
+                throw new RuntimeException("Duplicate constructor, " + c);
+            }
+            paramsToConstructor.put(c.getAssistedParameters(), c);
+        }
+
+        Map<Method, AssistedConstructor<?>> result = Maps.newHashMap();
+        for (Method method : factoryMethods) {
+            if (!method.getReturnType().isAssignableFrom(implementationType.getRawType())) {
+                throw newConfigurationException(
+                        "Return type of method %s is not assignable from %s", method, implementationType);
+            }
+
+            List<Type> parameterTypes = Lists.newArrayList();
+            for (TypeLiteral<?> parameterType : factoryType.getParameterTypes(method)) {
+                parameterTypes.add(parameterType.getType());
+            }
+            ParameterListKey methodParams = new ParameterListKey(parameterTypes);
+
+            if (!paramsToConstructor.containsKey(methodParams)) {
+                throw newConfigurationException(
+                        "%s has no @AssistInject constructor that takes the "
+                                + "@Assisted parameters %s in that order. @AssistInject constructors are %s",
+                        implementationType, methodParams, paramsToConstructor.values());
+            }
+
+            method.getParameterAnnotations();
+            for (Annotation[] parameterAnnotations : method.getParameterAnnotations()) {
+                for (Annotation parameterAnnotation : parameterAnnotations) {
+                    if (parameterAnnotation.annotationType() == Assisted.class) {
+                        throw newConfigurationException(
+                                "Factory method %s has an @Assisted parameter, which is incompatible with the"
+                                        + " deprecated @AssistedInject annotation. Please replace @AssistedInject with"
+                                        + " @Inject on the %s constructor.",
+                                method, implementationType);
+                    }
+                }
+            }
+
+            AssistedConstructor<?> matchingConstructor = paramsToConstructor.remove(methodParams);
+
+            result.put(method, matchingConstructor);
+        }
+        return result;
+    }
+
+    @Override
     public Set<Dependency<?>> getDependencies() {
         List<Dependency<?>> dependencies = Lists.newArrayList();
         for (AssistedConstructor<?> constructor : factoryMethodToConstructor.values()) {
@@ -314,9 +337,13 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
         return ImmutableSet.copyOf(dependencies);
     }
 
+    @Override
     public F get() {
-        InvocationHandler invocationHandler = new InvocationHandler() {
+        InvocationHandler invocationHandler =
-            public Object invoke(Object proxy, Method method, Object[] creationArgs) throws Throwable {
+                new InvocationHandler() {
+                    @Override
+                    public Object invoke(Object proxy, Method method, Object[] creationArgs)
+                            throws Throwable {
                         // pass methods from Object.class to the proxy
                         if (method.getDeclaringClass().equals(Object.class)) {
                             if ("equals".equals(method.getName())) {
@@ -336,8 +363,7 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
                     }
 
                     public Object[] gatherArgsForConstructor(
-                    AssistedConstructor<?> constructor,
+                            AssistedConstructor<?> constructor, Object[] factoryArgs) {
-                    Object[] factoryArgs) {
                         int numParams = constructor.getAllParameters().size();
                         int argPosition = 0;
                         Object[] result = new Object[numParams];
@@ -356,9 +382,10 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
                 };
 
         @SuppressWarnings("unchecked") // we imprecisely treat the class literal of T as a Class<T>
-        Class<F> factoryRawType = (Class<F>) factoryType.getRawType();
+        Class<F> factoryRawType = (Class<F>) (Class<?>) factoryType.getRawType();
-        return factoryRawType.cast(Proxy.newProxyInstance(factoryRawType.getClassLoader(),
+        return factoryRawType.cast(
-                new Class<?>[]{factoryRawType}, invocationHandler));
+                Proxy.newProxyInstance(
+                        factoryRawType.getClassLoader(), new Class<?>[] {factoryRawType}, invocationHandler));
     }
 
     @Override
@@ -375,4 +402,8 @@ public class FactoryProvider<F> implements Provider<F>, HasDependencies {
         return factoryType.equals(other.factoryType)
                 && implementationType.equals(other.implementationType);
     }
+
+    private static ConfigurationException newConfigurationException(String format, Object... args) {
+        return new ConfigurationException(ImmutableSet.of(new Message(Errors.format(format, args))));
+    }
 }

src/main/java/com/google/inject/assistedinject/FactoryProvider2.java

@@ -1,5 +1,8 @@
 package com.google.inject.assistedinject;
 
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.common.collect.Iterables.getOnlyElement;
+
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
 import com.google.common.collect.HashMultimap;
@@ -36,11 +39,12 @@ import com.google.inject.spi.ProviderInstanceBinding;
 import com.google.inject.spi.ProviderWithExtensionVisitor;
 import com.google.inject.spi.Toolable;
 import com.google.inject.util.Providers;
-
 import java.lang.annotation.Annotation;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationHandler;
-import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.lang.reflect.Proxy;
@@ -51,35 +55,46 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
-import static com.google.common.base.Preconditions.checkState;
-import static com.google.common.collect.Iterables.getOnlyElement;
-
 /**
- * The newer implementation of factory provider. This implementation uses a child injector to
+ * The newer implementation of factory provider. This implementation uses a child injector to create
- * create values.
+ * values.
+ *
+ * @author jessewilson@google.com (Jesse Wilson)
+ * @author dtm@google.com (Daniel Martin)
+ * @author schmitt@google.com (Peter Schmitt)
+ * @author sameb@google.com (Sam Berlin)
  */
-final class FactoryProvider2<F> implements InvocationHandler,
+final class FactoryProvider2<F>
-        ProviderWithExtensionVisitor<F>, HasDependencies, AssistedInjectBinding<F> {
+        implements InvocationHandler,
+        ProviderWithExtensionVisitor<F>,
+        HasDependencies,
+        AssistedInjectBinding<F> {
 
-    /**
+    /** A constant annotation to denote the return value, instead of creating a new one each time. */
-     * A constant annotation to denote the return value, instead of creating a new one each time.
-     */
     static final Annotation RETURN_ANNOTATION = UniqueAnnotations.create();
 
     // use the logger under a well-known name, not FactoryProvider2
     static final Logger logger = Logger.getLogger(AssistedInject.class.getName());
 
     /**
-     * if a factory method parameter isn't annotated, it gets this annotation.
+     * A constant that determines if we allow fallback to reflection. Typically always true, but
+     * reflectively set to false in tests.
      */
-    static final Assisted DEFAULT_ANNOTATION = new Assisted() {
+    private static boolean allowLookupReflection = true;
+
+    /** if a factory method parameter isn't annotated, it gets this annotation. */
+    static final Assisted DEFAULT_ANNOTATION =
+            new Assisted() {
+                @Override
                 public String value() {
                     return "";
                 }
 
+                @Override
                 public Class<? extends Annotation> annotationType() {
                     return Assisted.class;
                 }
@@ -96,40 +111,117 @@ final class FactoryProvider2<F> implements InvocationHandler,
 
                 @Override
                 public String toString() {
-            return "@" + Assisted.class.getName() + "(value=\"\")";
+                    return "@"
+                            + Assisted.class.getName()
+                            + "("
+                            + Annotations.memberValueString("value", "")
+                            + ")";
                 }
             };
-    /**
+
-     * Mapping from method to the data about how the method will be assisted.
+    /** All the data necessary to perform an assisted inject. */
-     */
+    private static class AssistData implements AssistedMethod {
+        /** the constructor the implementation is constructed with. */
+        final Constructor<?> constructor;
+        /** the return type in the factory method that the constructor is bound to. */
+        final Key<?> returnType;
+        /** the parameters in the factory method associated with this data. */
+        final ImmutableList<Key<?>> paramTypes;
+        /** the type of the implementation constructed */
+        final TypeLiteral<?> implementationType;
+
+        /** All non-assisted dependencies required by this method. */
+        final Set<Dependency<?>> dependencies;
+        /** The factory method associated with this data */
+        final Method factoryMethod;
+
+        /** true if {@link #isValidForOptimizedAssistedInject} returned true. */
+        final boolean optimized;
+        /** the list of optimized providers, empty if not optimized. */
+        final List<ThreadLocalProvider> providers;
+        /** used to perform optimized factory creations. */
+        volatile Binding<?> cachedBinding; // TODO: volatile necessary?
+
+        AssistData(
+                Constructor<?> constructor,
+                Key<?> returnType,
+                ImmutableList<Key<?>> paramTypes,
+                TypeLiteral<?> implementationType,
+                Method factoryMethod,
+                Set<Dependency<?>> dependencies,
+                boolean optimized,
+                List<ThreadLocalProvider> providers) {
+            this.constructor = constructor;
+            this.returnType = returnType;
+            this.paramTypes = paramTypes;
+            this.implementationType = implementationType;
+            this.factoryMethod = factoryMethod;
+            this.dependencies = dependencies;
+            this.optimized = optimized;
+            this.providers = providers;
+        }
+
+        @Override
+        public String toString() {
+            return MoreObjects.toStringHelper(getClass())
+                    .add("ctor", constructor)
+                    .add("return type", returnType)
+                    .add("param type", paramTypes)
+                    .add("implementation type", implementationType)
+                    .add("dependencies", dependencies)
+                    .add("factory method", factoryMethod)
+                    .add("optimized", optimized)
+                    .add("providers", providers)
+                    .add("cached binding", cachedBinding)
+                    .toString();
+        }
+
+        @Override
+        public Set<Dependency<?>> getDependencies() {
+            return dependencies;
+        }
+
+        @Override
+        public Method getFactoryMethod() {
+            return factoryMethod;
+        }
+
+        @Override
+        public Constructor<?> getImplementationConstructor() {
+            return constructor;
+        }
+
+        @Override
+        public TypeLiteral<?> getImplementationType() {
+            return implementationType;
+        }
+    }
+
+    /** Mapping from method to the data about how the method will be assisted. */
     private final ImmutableMap<Method, AssistData> assistDataByMethod;
-    /**
+
-     * Mapping from method to method handle, for generated default methods.
+    /** Mapping from method to method handle, for generated default methods. */
-     */
+    private final ImmutableMap<Method, MethodHandle> methodHandleByMethod;
-    private final ImmutableMap<Method, MethodHandleWrapper> methodHandleByMethod;
+
-    /**
+    /** the hosting injector, or null if we haven't been initialized yet */
-     * the factory interface, implemented and provided
-     */
-    private final F factory;
-    /**
-     * The key that this is bound to.
-     */
-    private final Key<F> factoryKey;
-    /**
-     * The binding collector, for equality/hashing purposes.
-     */
-    private final BindingCollector collector;
-    /**
-     * the hosting injector, or null if we haven't been initialized yet
-     */
     private Injector injector;
 
+    /** the factory interface, implemented and provided */
+    private final F factory;
+
+    /** The key that this is bound to. */
+    private final Key<F> factoryKey;
+
+    /** The binding collector, for equality/hashing purposes. */
+    private final BindingCollector collector;
+
     /**
      * @param factoryKey a key for a Java interface that defines one or more create methods.
-     * @param collector  binding configuration that maps method return types to
+     * @param collector binding configuration that maps method return types to implementation types.
-     *                   implementation types.
+     * @param userLookups user provided lookups, optional.
      */
-    FactoryProvider2(Key<F> factoryKey, BindingCollector collector) {
+    FactoryProvider2(
+            Key<F> factoryKey, BindingCollector collector, MethodHandles.Lookup userLookups) {
         this.factoryKey = factoryKey;
         this.collector = collector;
 
@@ -149,6 +241,11 @@ final class FactoryProvider2<F> implements InvocationHandler,
             ImmutableMap.Builder<Method, AssistData> assistDataBuilder = ImmutableMap.builder();
             // TODO: also grab methods from superinterfaces
             for (Method method : factoryRawType.getMethods()) {
+                // Skip static methods
+                if (Modifier.isStatic(method.getModifiers())) {
+                    continue;
+                }
+
                 // Skip default methods that java8 may have created.
                 if (isDefault(method) && (method.isBridge() || method.isSynthetic())) {
                     // Even synthetic default methods need the return type validation...
@@ -162,7 +259,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
                 TypeLiteral<?> returnTypeLiteral = factoryType.getReturnType(method);
                 Key<?> returnType;
                 try {
-                    returnType = Annotations.getKey(returnTypeLiteral, method, method.getAnnotations(), errors);
+                    returnType =
+                            Annotations.getKey(returnTypeLiteral, method, method.getAnnotations(), errors);
                 } catch (ConfigurationException ce) {
                     // If this was an error due to returnTypeLiteral not being specified, rephrase
                     // it as our factory not being specified, so it makes more sense to users.
@@ -182,7 +280,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
                     Class<?> underlylingType = paramKey.getTypeLiteral().getRawType();
                     if (underlylingType.equals(Provider.class)
                             || underlylingType.equals(javax.inject.Provider.class)) {
-                        errors.addMessage("A Provider may not be a type in a factory method of an AssistedInject."
+                        errors.addMessage(
+                                "A Provider may not be a type in a factory method of an AssistedInject."
                                         + "\n  Offending instance is parameter [%s] with key [%s] on method [%s]",
                                 p, paramKey, method);
                     }
@@ -198,7 +297,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
                 Class<? extends Annotation> scope =
                         Annotations.findScopeAnnotation(errors, implementation.getRawType());
                 if (scope != null) {
-                    errors.addMessage("Found scope annotation [%s] on implementation class "
+                    errors.addMessage(
+                            "Found scope annotation [%s] on implementation class "
                                     + "[%s] of AssistedInject factory [%s].\nThis is not allowed, please"
                                     + " remove the scope annotation.",
                             scope, implementation.getRawType(), factoryType);
@@ -207,7 +307,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
                 InjectionPoint ctorInjectionPoint;
                 try {
                     ctorInjectionPoint =
-                            findMatchingConstructorInjectionPoint(method, returnType, implementation, immutableParamList);
+                            findMatchingConstructorInjectionPoint(
+                                    method, returnType, implementation, immutableParamList);
                 } catch (ErrorsException ee) {
                     errors.merge(ee.getErrors());
                     continue;
@@ -231,7 +332,9 @@ final class FactoryProvider2<F> implements InvocationHandler,
                     optimized = true;
                 }
 
-                AssistData data = new AssistData(constructor,
+                AssistData data =
+                        new AssistData(
+                                constructor,
                                 returnType,
                                 immutableParamList,
                                 implementation,
@@ -242,25 +345,61 @@ final class FactoryProvider2<F> implements InvocationHandler,
                 assistDataBuilder.put(method, data);
             }
 
-            factory = factoryRawType.cast(Proxy.newProxyInstance(
+            factory =
+                    factoryRawType.cast(
+                            Proxy.newProxyInstance(
                                     factoryRawType.getClassLoader(), new Class<?>[] {factoryRawType}, this));
 
             // Now go back through default methods. Try to use MethodHandles to make things
             // work.  If that doesn't work, fallback to trying to find compatible method
             // signatures.
             Map<Method, AssistData> dataSoFar = assistDataBuilder.build();
-            ImmutableMap.Builder<Method, MethodHandleWrapper> methodHandleBuilder = ImmutableMap.builder();
+            ImmutableMap.Builder<Method, MethodHandle> methodHandleBuilder = ImmutableMap.builder();
+            boolean warnedAboutUserLookups = false;
             for (Map.Entry<String, Method> entry : defaultMethods.entries()) {
+                if (!warnedAboutUserLookups
+                        && userLookups == null
+                        && !Modifier.isPublic(factory.getClass().getModifiers())) {
+                    warnedAboutUserLookups = true;
+                    logger.log(
+                            Level.WARNING,
+                            "AssistedInject factory {0} is non-public and has javac-generated default methods. "
+                                    + " Please pass a `MethodHandles.lookups()` with"
+                                    + " FactoryModuleBuilder.withLookups when using this factory so that Guice can"
+                                    + " properly call the default methods. Guice will try to work around the"
+                                    + " problem, but doing so requires reflection into the JDK and may break at any"
+                                    + " time.",
+                            new Object[] {factoryType});
+                }
+
                 Method defaultMethod = entry.getValue();
-                MethodHandleWrapper handle = MethodHandleWrapper.create(defaultMethod, factory);
+                MethodHandle handle = null;
+                try {
+                    // Note: this can return null if we fallback to reflecting the private lookup cxtor and it
+                    // fails. In that case, we try the super hacky workaround below (w/ 'foundMatch').
+                    // It can throw an exception if we're not doing private reflection, or if unreflectSpecial
+                    // _still_ fails.
+                    handle = superMethodHandle(defaultMethod, factory, userLookups);
+                } catch (ReflectiveOperationException roe) {
+                    errors.addMessage(
+                            new Message(
+                                    "Unable to use factory "
+                                            + factoryRawType.getName()
+                                            + ". Did you call FactoryModuleBuilder.withLookups(MethodHandles.lookups())"
+                                            + " (with a lookups that has access to the factory)?"));
+                    continue;
+                }
+
                 if (handle != null) {
                     methodHandleBuilder.put(defaultMethod, handle);
                 } else {
+                    // TODO: remove this workaround when Java8 support is dropped
                     boolean foundMatch = false;
                     for (Method otherMethod : otherMethods.get(defaultMethod.getName())) {
                         if (dataSoFar.containsKey(otherMethod) && isCompatible(defaultMethod, otherMethod)) {
                             if (foundMatch) {
-                                errors.addMessage("Generated default method %s with parameters %s is"
+                                errors.addMessage(
+                                        "Generated default method %s with parameters %s is"
                                                 + " signature-compatible with more than one non-default method."
                                                 + " Unable to create factory. As a workaround, remove the override"
                                                 + " so javac stops generating a default method.",
@@ -277,7 +416,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
                 }
             }
 
-            // If we generated any errors (from finding matching constructors, for instance), throw an exception.
+            // If we generated any errors (from finding matching constructors, for instance), throw an
+            // exception.
             if (errors.hasErrors()) {
                 throw errors.toException();
             }
@@ -297,23 +437,6 @@ final class FactoryProvider2<F> implements InvocationHandler,
                 == Modifier.PUBLIC;
     }
 
-    /**
-     * Returns true if {@code thrown} can be thrown by {@code invoked} without wrapping.
-     */
-    static boolean canRethrow(Method invoked, Throwable thrown) {
-        if (thrown instanceof Error || thrown instanceof RuntimeException) {
-            return true;
-        }
-
-        for (Class<?> declared : invoked.getExceptionTypes()) {
-            if (declared.isInstance(thrown)) {
-                return true;
-            }
-        }
-
-        return false;
-    }
-
     private boolean isCompatible(Method src, Method dst) {
         if (!src.getReturnType().isAssignableFrom(dst.getReturnType())) {
             return false;
@@ -331,32 +454,37 @@ final class FactoryProvider2<F> implements InvocationHandler,
         return true;
     }
 
+    @Override
     public F get() {
         return factory;
     }
 
+    @Override
     public Set<Dependency<?>> getDependencies() {
-        Set<Dependency<?>> combinedDeps = new HashSet<Dependency<?>>();
+        Set<Dependency<?>> combinedDeps = new HashSet<>();
         for (AssistData data : assistDataByMethod.values()) {
             combinedDeps.addAll(data.dependencies);
         }
         return ImmutableSet.copyOf(combinedDeps);
     }
 
+    @Override
     public Key<F> getKey() {
         return factoryKey;
     }
 
     // Safe cast because values are typed to AssistedData, which is an AssistedMethod, and
     // the collection is immutable.
+    @Override
     @SuppressWarnings("unchecked")
     public Collection<AssistedMethod> getAssistedMethods() {
         return (Collection<AssistedMethod>) (Collection<?>) assistDataByMethod.values();
     }
 
+    @Override
     @SuppressWarnings("unchecked")
-    public <T, V> V acceptExtensionVisitor(BindingTargetVisitor<T, V> visitor,
+    public <T, V> V acceptExtensionVisitor(
-                                           ProviderInstanceBinding<? extends T> binding) {
+            BindingTargetVisitor<T, V> visitor, ProviderInstanceBinding<? extends T> binding) {
         if (visitor instanceof AssistedInjectTargetVisitor) {
             return ((AssistedInjectTargetVisitor<T, V>) visitor).visit((AssistedInjectBinding<T>) this);
         }
@@ -366,7 +494,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
     private void validateFactoryReturnType(Errors errors, Class<?> returnType, Class<?> factoryType) {
         if (Modifier.isPublic(factoryType.getModifiers())
                 && !Modifier.isPublic(returnType.getModifiers())) {
-            errors.addMessage("%s is public, but has a method that returns a non-public type: %s. "
+            errors.addMessage(
+                    "%s is public, but has a method that returns a non-public type: %s. "
                             + "Due to limitations with java.lang.reflect.Proxy, this is not allowed. "
                             + "Please either make the factory non-public or the return type public.",
                     factoryType, returnType);
@@ -380,8 +509,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
     private boolean isTypeNotSpecified(TypeLiteral<?> typeLiteral, ConfigurationException ce) {
         Collection<Message> messages = ce.getErrorMessages();
         if (messages.size() == 1) {
-            Message msg = Iterables.getOnlyElement(
+            Message msg =
-                    new Errors().keyNotFullySpecified(typeLiteral).getMessages());
+                    Iterables.getOnlyElement(new Errors().keyNotFullySpecified(typeLiteral).getMessages());
             return msg.getMessage().equals(Iterables.getOnlyElement(messages).getMessage());
         } else {
             return false;
@@ -391,9 +520,9 @@ final class FactoryProvider2<F> implements InvocationHandler,
     /**
      * Finds a constructor suitable for the method. If the implementation contained any constructors
      * marked with {@link AssistedInject}, this requires all {@link Assisted} parameters to exactly
-     * match the parameters (in any order) listed in the method.  Otherwise, if no
+     * match the parameters (in any order) listed in the method. Otherwise, if no {@link
-     * {@link AssistedInject} constructors exist, this will default to looking for an
+     * AssistedInject} constructors exist, this will default to looking for an {@literal @}{@link
-     * {@literal @}{@link Inject} constructor.
+     * Inject} constructor.
      */
     private <T> InjectionPoint findMatchingConstructorInjectionPoint(
             Method method, Key<?> returnType, TypeLiteral<T> implementation, List<Key<?>> paramList)
@@ -429,8 +558,7 @@ final class FactoryProvider2<F> implements InvocationHandler,
                 anyAssistedInjectConstructors = true;
                 if (constructorHasMatchingParams(implementation, constructor, paramList, errors)) {
                     if (matchingConstructor != null) {
-                        errors
+                        errors.addMessage(
-                                .addMessage(
                                 "%s has more than one constructor annotated with @AssistedInject"
                                         + " that matches the parameters in method %s.  Unable to create "
                                         + "AssistedInject factory.",
@@ -444,7 +572,7 @@ final class FactoryProvider2<F> implements InvocationHandler,
         }
 
         if (!anyAssistedInjectConstructors) {
-            // If none existed, use @Inject.
+            // If none existed, use @Inject or a no-arg constructor.
             try {
                 return InjectionPoint.forConstructorOf(implementation);
             } catch (ConfigurationException e) {
@@ -456,7 +584,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
             if (matchingConstructor != null) {
                 // safe because we got the constructor from this implementation.
                 @SuppressWarnings("unchecked")
-                InjectionPoint ip = InjectionPoint.forConstructor(
+                InjectionPoint ip =
+                        InjectionPoint.forConstructor(
                                 (Constructor<? super T>) matchingConstructor, implementation);
                 return ip;
             } else {
@@ -470,21 +599,19 @@ final class FactoryProvider2<F> implements InvocationHandler,
     }
 
     /**
-     * Matching logic for constructors annotated with AssistedInject.
+     * Matching logic for constructors annotated with AssistedInject. This returns true if and only if
-     * This returns true if and only if all @Assisted parameters in the
+     * all @Assisted parameters in the constructor exactly match (in any order) all @Assisted
-     * constructor exactly match (in any order) all @Assisted parameters
+     * parameters the method's parameter.
-     * the method's parameter.
      */
-    private boolean constructorHasMatchingParams(TypeLiteral<?> type,
+    private boolean constructorHasMatchingParams(
-                                                 Constructor<?> constructor, List<Key<?>> paramList, Errors errors)
+            TypeLiteral<?> type, Constructor<?> constructor, List<Key<?>> paramList, Errors errors)
             throws ErrorsException {
         List<TypeLiteral<?>> params = type.getParameterTypes(constructor);
         Annotation[][] paramAnnotations = constructor.getParameterAnnotations();
         int p = 0;
         List<Key<?>> constructorKeys = Lists.newArrayList();
         for (TypeLiteral<?> param : params) {
-            Key<?> paramKey = Annotations.getKey(param, constructor, paramAnnotations[p++],
+            Key<?> paramKey = Annotations.getKey(param, constructor, paramAnnotations[p++], errors);
-                    errors);
             constructorKeys.add(paramKey);
         }
         // Require that every key exist in the constructor to match up exactly.
@@ -504,10 +631,9 @@ final class FactoryProvider2<F> implements InvocationHandler,
         return true;
     }
 
-    /**
+    /** Calculates all dependencies required by the implementation and constructor. */
-     * Calculates all dependencies required by the implementation and constructor.
+    private Set<Dependency<?>> getDependencies(
-     */
+            InjectionPoint ctorPoint, TypeLiteral<?> implementation) {
-    private Set<Dependency<?>> getDependencies(InjectionPoint ctorPoint, TypeLiteral<?> implementation) {
         ImmutableSet.Builder<Dependency<?>> builder = ImmutableSet.builder();
         builder.addAll(ctorPoint.getDependencies());
         if (!implementation.getRawType().isInterface()) {
@@ -518,9 +644,7 @@ final class FactoryProvider2<F> implements InvocationHandler,
         return builder.build();
     }
 
-    /**
+    /** Return all non-assisted dependencies. */
-     * Return all non-assisted dependencies.
-     */
     private Set<Dependency<?>> removeAssistedDeps(Set<Dependency<?>> deps) {
         ImmutableSet.Builder<Dependency<?>> builder = ImmutableSet.builder();
         for (Dependency<?> dep : deps) {
@@ -538,8 +662,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
      * the assisted bindings are immediately provided. This looks for hints that the values may be
      * lazily retrieved, by looking for injections of Injector or a Provider for the assisted values.
      */
-    private boolean isValidForOptimizedAssistedInject(Set<Dependency<?>> dependencies,
+    private boolean isValidForOptimizedAssistedInject(
-                                                      Class<?> implementation, TypeLiteral<?> factoryType) {
+            Set<Dependency<?>> dependencies, Class<?> implementation, TypeLiteral<?> factoryType) {
         Set<Dependency<?>> badDeps = null; // optimization: create lazily
         for (Dependency<?> dep : dependencies) {
             if (isInjectorOrAssistedProvider(dep)) {
@@ -550,7 +674,9 @@ final class FactoryProvider2<F> implements InvocationHandler,
             }
         }
         if (badDeps != null && !badDeps.isEmpty()) {
-            logger.log(Level.WARNING, "AssistedInject factory {0} will be slow "
+            logger.log(
+                    Level.WARNING,
+                    "AssistedInject factory {0} will be slow "
                             + "because {1} has assisted Provider dependencies or injects the Injector. "
                             + "Stop injecting @Assisted Provider<T> (instead use @Assisted T) "
                             + "or Injector to speed things up. (It will be a ~6500% speed bump!)  "
@@ -562,33 +688,43 @@ final class FactoryProvider2<F> implements InvocationHandler,
     }
 
     /**
-     * Returns true if the dependency is for {@link Injector} or if the dependency
+     * Returns true if the dependency is for {@link Injector} or if the dependency is a {@link
-     * is a {@link Provider} for a parameter that is {@literal @}{@link Assisted}.
+     * Provider} for a parameter that is {@literal @}{@link Assisted}.
      */
     private boolean isInjectorOrAssistedProvider(Dependency<?> dependency) {
         Class<?> annotationType = dependency.getKey().getAnnotationType();
         if (annotationType != null && annotationType.equals(Assisted.class)) { // If it's assisted..
-            if (dependency.getKey().getTypeLiteral().getRawType().equals(Provider.class)) { // And a Provider...
+            if (dependency
+                    .getKey()
+                    .getTypeLiteral()
+                    .getRawType()
+                    .equals(Provider.class)) { // And a Provider...
                 return true;
             }
-        } else if (dependency.getKey().getTypeLiteral().getRawType().equals(Injector.class)) { // If it's the Injector...
+        } else if (dependency
+                .getKey()
+                .getTypeLiteral()
+                .getRawType()
+                .equals(Injector.class)) { // If it's the Injector...
             return true;
         }
         return false;
     }
 
     /**
-     * Returns a key similar to {@code key}, but with an {@literal @}Assisted binding annotation.
+     * Returns a key similar to {@code key}, but with an {@literal @}Assisted binding annotation. This
-     * This fails if another binding annotation is clobbered in the process. If the key already has
+     * fails if another binding annotation is clobbered in the process. If the key already has the
-     * the {@literal @}Assisted annotation, it is returned as-is to preserve any String value.
+     * {@literal @}Assisted annotation, it is returned as-is to preserve any String value.
      */
     private <T> Key<T> assistKey(Method method, Key<T> key, Errors errors) throws ErrorsException {
         if (key.getAnnotationType() == null) {
-            return Key.get(key.getTypeLiteral(), DEFAULT_ANNOTATION);
+            return key.withAnnotation(DEFAULT_ANNOTATION);
         } else if (key.getAnnotationType() == Assisted.class) {
             return key;
         } else {
-            errors.withSource(method).addMessage(
+            errors
+                    .withSource(method)
+                    .addMessage(
                             "Only @Assisted is allowed for factory parameters, but found @%s",
                             key.getAnnotationType());
             throw errors.toException();
@@ -596,14 +732,17 @@ final class FactoryProvider2<F> implements InvocationHandler,
     }
 
     /**
-     * At injector-creation time, we initialize the invocation handler. At this time we make sure
+     * At injector-creation time, we initialize the invocation handler. At this time we make sure all
-     * all factory methods will be able to build the target types.
+     * factory methods will be able to build the target types.
      */
     @Inject
     @Toolable
     void initialize(Injector injector) {
         if (this.injector != null) {
-            throw new ConfigurationException(ImmutableList.of(new Message(FactoryProvider2.class,
+            throw new ConfigurationException(
+                    ImmutableList.of(
+                            new Message(
+                                    FactoryProvider2.class,
                                     "Factories.create() factories may only be used in one Injector!")));
         }
 
@@ -619,7 +758,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
             } else {
                 args = null; // won't be used -- instead will bind to data.providers.
             }
-            getBindingFromNewInjector(method, args, data); // throws if the binding isn't properly configured
+            getBindingFromNewInjector(
+                    method, args, data); // throws if the binding isn't properly configured
         }
     }
 
@@ -628,7 +768,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
      */
     public Binding<?> getBindingFromNewInjector(
             final Method method, final Object[] args, final AssistData data) {
-        checkState(injector != null,
+        checkState(
+                injector != null,
                 "Factories.create() factories cannot be used until they're initialized by Guice.");
 
         final Key<?> returnType = data.returnType;
@@ -636,17 +777,21 @@ final class FactoryProvider2<F> implements InvocationHandler,
         // We ignore any pre-existing binding annotation.
         final Key<?> returnKey = Key.get(returnType.getTypeLiteral(), RETURN_ANNOTATION);
 
-        Module assistedModule = new AbstractModule() {
+        Module assistedModule =
+                new AbstractModule() {
                     @Override
                     @SuppressWarnings({
-                    "unchecked", "rawtypes"}) // raw keys are necessary for the args array and return value
+                            "unchecked",
+                            "rawtypes"
+                    }) // raw keys are necessary for the args array and return value
                     protected void configure() {
                         Binder binder = binder().withSource(method);
 
                         int p = 0;
                         if (!data.optimized) {
                             for (Key<?> paramKey : data.paramTypes) {
-                        // Wrap in a Provider to cover null, and to prevent Guice from injecting the parameter
+                                // Wrap in a Provider to cover null, and to prevent Guice from injecting the
+                                // parameter
                                 binder.bind((Key) paramKey).toProvider(Providers.of(args[p++]));
                             }
                         } else {
@@ -661,7 +806,8 @@ final class FactoryProvider2<F> implements InvocationHandler,
                         // but if it isn't, we'll end up throwing a fairly good error
                         // message for the user.
                         if (constructor != null) {
-                    binder.bind(returnKey)
+                            binder
+                                    .bind(returnKey)
                                     .toConstructor(constructor, (TypeLiteral) data.implementationType)
                                     .in(Scopes.NO_SCOPE); // make sure we erase any scope on the implementation type
                         }
@@ -681,6 +827,7 @@ final class FactoryProvider2<F> implements InvocationHandler,
      * When a factory method is invoked, we create a child injector that binds all parameters, then
      * use that to get an instance of the return type.
      */
+    @Override
     public Object invoke(Object proxy, final Method method, final Object[] args) throws Throwable {
         // If we setup a method handle earlier for this method, call it.
         // This is necessary for default methods that java8 creates, so we
@@ -749,93 +896,19 @@ final class FactoryProvider2<F> implements InvocationHandler,
         return factoryKey.equals(other.factoryKey) && Objects.equal(collector, other.collector);
     }
 
-    /**
+    /** Returns true if {@code thrown} can be thrown by {@code invoked} without wrapping. */
-     * All the data necessary to perform an assisted inject.
+    static boolean canRethrow(Method invoked, Throwable thrown) {
-     */
+        if (thrown instanceof Error || thrown instanceof RuntimeException) {
-    private static class AssistData implements AssistedMethod {
+            return true;
-        /**
-         * the constructor the implementation is constructed with.
-         */
-        final Constructor<?> constructor;
-        /**
-         * the return type in the factory method that the constructor is bound to.
-         */
-        final Key<?> returnType;
-        /**
-         * the parameters in the factory method associated with this data.
-         */
-        final ImmutableList<Key<?>> paramTypes;
-        /**
-         * the type of the implementation constructed
-         */
-        final TypeLiteral<?> implementationType;
-
-        /**
-         * All non-assisted dependencies required by this method.
-         */
-        final Set<Dependency<?>> dependencies;
-        /**
-         * The factory method associated with this data
-         */
-        final Method factoryMethod;
-
-        /**
-         * true if {@link #isValidForOptimizedAssistedInject} returned true.
-         */
-        final boolean optimized;
-        /**
-         * the list of optimized providers, empty if not optimized.
-         */
-        final List<ThreadLocalProvider> providers;
-        /**
-         * used to perform optimized factory creations.
-         */
-        volatile Binding<?> cachedBinding; // TODO: volatile necessary?
-
-        AssistData(Constructor<?> constructor, Key<?> returnType, ImmutableList<Key<?>> paramTypes,
-                   TypeLiteral<?> implementationType, Method factoryMethod,
-                   Set<Dependency<?>> dependencies,
-                   boolean optimized, List<ThreadLocalProvider> providers) {
-            this.constructor = constructor;
-            this.returnType = returnType;
-            this.paramTypes = paramTypes;
-            this.implementationType = implementationType;
-            this.factoryMethod = factoryMethod;
-            this.dependencies = dependencies;
-            this.optimized = optimized;
-            this.providers = providers;
         }
 
-        @Override
+        for (Class<?> declared : invoked.getExceptionTypes()) {
-        public String toString() {
+            if (declared.isInstance(thrown)) {
-            return MoreObjects.toStringHelper(getClass())
+                return true;
-                    .add("ctor", constructor)
+            }
-                    .add("return type", returnType)
-                    .add("param type", paramTypes)
-                    .add("implementation type", implementationType)
-                    .add("dependencies", dependencies)
-                    .add("factory method", factoryMethod)
-                    .add("optimized", optimized)
-                    .add("providers", providers)
-                    .add("cached binding", cachedBinding)
-                    .toString();
         }
 
-        public Set<Dependency<?>> getDependencies() {
+        return false;
-            return dependencies;
-        }
-
-        public Method getFactoryMethod() {
-            return factoryMethod;
-        }
-
-        public Constructor<?> getImplementationConstructor() {
-            return constructor;
-        }
-
-        public TypeLiteral<?> getImplementationType() {
-            return implementationType;
-        }
     }
 
     // not <T> because we'll never know and this is easier than suppressing warnings.
@@ -848,86 +921,106 @@ final class FactoryProvider2<F> implements InvocationHandler,
         }
     }
 
-    /**
+    private static MethodHandle superMethodHandle(
-     * Wrapper around MethodHandles/MethodHandle, so we can compile+run on java6.
+            Method method, Object proxy, MethodHandles.Lookup userLookups)
-     */
+            throws ReflectiveOperationException {
-    private static class MethodHandleWrapper {
+        MethodHandles.Lookup lookup = userLookups == null ? MethodHandles.lookup() : userLookups;
-        static final int ALL_MODES = Modifier.PRIVATE
+        MethodHandle handle = SUPER_METHOD_LOOKUP.get().superMethodHandle(method, lookup);
-                | Modifier.STATIC /* package */
+        return handle != null ? handle.bindTo(proxy) : null;
-                | Modifier.PUBLIC
+    }
-                | Modifier.PROTECTED;
 
-        static final Method unreflectSpecial;
+    // begin by trying unreflectSpecial to find super method handles; this should work on Java14+
-        static final Method bindTo;
+    private static final AtomicReference<SuperMethodLookup> SUPER_METHOD_LOOKUP =
-        static final Method invokeWithArguments;
+            new AtomicReference<>(SuperMethodLookup.UNREFLECT_SPECIAL);
-        static final Constructor<?> lookupCxtor;
-        static final boolean valid;
 
-        static {
+    private static enum SuperMethodLookup {
-            Method unreflectSpecialTmp = null;
+        UNREFLECT_SPECIAL {
-            Method bindToTmp = null;
+            @Override
-            Method invokeWithArgumentsTmp = null;
+            MethodHandle superMethodHandle(Method method, MethodHandles.Lookup lookup)
-            boolean validTmp = false;
+                    throws ReflectiveOperationException {
-            Constructor<?> lookupCxtorTmp = null;
                 try {
-                Class<?> lookupClass = Class.forName("java.lang.invoke.MethodHandles$Lookup");
+                    return lookup.unreflectSpecial(method, method.getDeclaringClass());
-                unreflectSpecialTmp = lookupClass.getMethod("unreflectSpecial", Method.class, Class.class);
+                } catch (ReflectiveOperationException e) {
-                Class<?> methodHandleClass = Class.forName("java.lang.invoke.MethodHandle");
+                    // fall back to findSpecial which should work on Java9+; use that for future lookups
-                bindToTmp = methodHandleClass.getMethod("bindTo", Object.class);
+                    SUPER_METHOD_LOOKUP.compareAndSet(this, FIND_SPECIAL);
-                invokeWithArgumentsTmp = methodHandleClass.getMethod("invokeWithArguments", Object[].class);
+                    return SUPER_METHOD_LOOKUP.get().superMethodHandle(method, lookup);
-                lookupCxtorTmp = lookupClass.getDeclaredConstructor(Class.class, int.class);
-                lookupCxtorTmp.setAccessible(true);
-                validTmp = true;
-            } catch (Exception invalid) {
-                // Ignore the exception, store the values & exit early in create(..) if invalid.
                 }
-
-            // Store refs to later.
-            valid = validTmp;
-            unreflectSpecial = unreflectSpecialTmp;
-            bindTo = bindToTmp;
-            invokeWithArguments = invokeWithArgumentsTmp;
-            lookupCxtor = lookupCxtorTmp;
-        }
-
-        final Object handle;
-
-        MethodHandleWrapper(Object handle) {
-            this.handle = handle;
-        }
-
-        static MethodHandleWrapper create(Method method, Object proxy) {
-            if (!valid) {
-                return null;
             }
+        },
+        FIND_SPECIAL {
+            @Override
+            MethodHandle superMethodHandle(Method method, MethodHandles.Lookup lookup)
+                    throws ReflectiveOperationException {
                 try {
                     Class<?> declaringClass = method.getDeclaringClass();
-                // Note: this isn't a public API, but we need to use it in order to call default methods.
+                    // use findSpecial to workaround https://bugs.openjdk.java.net/browse/JDK-8209005
-                Object lookup = lookupCxtor.newInstance(declaringClass, ALL_MODES);
+                    return lookup.findSpecial(
-                method.setAccessible(true);
+                            declaringClass,
-                // These are part of the public API, but we use reflection since we run on java6
+                            method.getName(),
-                // and they were introduced in java7.
+                            MethodType.methodType(method.getReturnType(), method.getParameterTypes()),
-                lookup = unreflectSpecial.invoke(lookup, method, declaringClass);
+                            declaringClass);
-                Object handle = bindTo.invoke(lookup, proxy);
+                } catch (ReflectiveOperationException e) {
-                return new MethodHandleWrapper(handle);
+                    if (!allowLookupReflection) {
-            } catch (InvocationTargetException ite) {
+                        throw e;
-                return null;
+                    }
-            } catch (IllegalAccessException iae) {
+                    // fall back to private Lookup which should work on Java8; use that for future lookups
-                return null;
+                    SUPER_METHOD_LOOKUP.compareAndSet(this, PRIVATE_LOOKUP);
-            } catch (InstantiationException ie) {
+                    return SUPER_METHOD_LOOKUP.get().superMethodHandle(method, lookup);
-                return null;
                 }
             }
-
+        },
-        Object invokeWithArguments(Object[] args) throws Exception {
+        PRIVATE_LOOKUP {
-            // We must cast the args to an object so the Object[] is the first param,
-            // as opposed to each individual varargs param.
-            return invokeWithArguments.invoke(handle, (Object) args);
-        }
-
             @Override
-        public String toString() {
+            MethodHandle superMethodHandle(Method method, MethodHandles.Lookup unused)
-            return handle.toString();
+                    throws ReflectiveOperationException {
+                return PrivateLookup.superMethodHandle(method);
+            }
+        };
+
+        abstract MethodHandle superMethodHandle(Method method, MethodHandles.Lookup lookup)
+                throws ReflectiveOperationException;
+    };
+
+    // Note: this isn't a public API, but we need to use it in order to call default methods on (or
+    // with) non-public types. If it doesn't exist, the code falls back to a less precise check.
+    static class PrivateLookup {
+        PrivateLookup() {}
+
+        private static final int ALL_MODES =
+                Modifier.PRIVATE | Modifier.STATIC /* package */ | Modifier.PUBLIC | Modifier.PROTECTED;
+
+        private static final Constructor<MethodHandles.Lookup> privateLookupCxtor =
+                findPrivateLookupCxtor();
+
+        private static Constructor<MethodHandles.Lookup> findPrivateLookupCxtor() {
+            try {
+                Constructor<MethodHandles.Lookup> cxtor;
+                try {
+                    cxtor = MethodHandles.Lookup.class.getDeclaredConstructor(Class.class, int.class);
+                } catch (NoSuchMethodException ignored) {
+                    cxtor =
+                            MethodHandles.Lookup.class.getDeclaredConstructor(
+                                    Class.class, Class.class, int.class);
+                }
+                cxtor.setAccessible(true);
+                return cxtor;
+            } catch (ReflectiveOperationException | SecurityException e) {
+                return null;
+            }
+        }
+
+        static MethodHandle superMethodHandle(Method method) throws ReflectiveOperationException {
+            if (privateLookupCxtor == null) {
+                return null; // fall back to assistDataBuilder workaround
+            }
+            Class<?> declaringClass = method.getDeclaringClass();
+            MethodHandles.Lookup lookup;
+            if (privateLookupCxtor.getParameterCount() == 2) {
+                lookup = privateLookupCxtor.newInstance(declaringClass, ALL_MODES);
+            } else {
+                lookup = privateLookupCxtor.newInstance(declaringClass, null, ALL_MODES);
+            }
+            return lookup.unreflectSpecial(method, declaringClass);
         }
     }
 }

src/main/java/com/google/inject/internal/AbstractBindingProcessor.java

@@ -14,17 +14,16 @@ import com.google.inject.Stage;
 import com.google.inject.TypeLiteral;
 import com.google.inject.spi.DefaultBindingTargetVisitor;
 
-import java.util.Set;
-
 /**
  * Guarantees that processing of Binding elements happens in a sane way.
  */
 abstract class AbstractBindingProcessor extends AbstractProcessor {
 
-    // It's unfortunate that we have to maintain a blacklist of specific
+    // It's unfortunate that we have to maintain a list of specific
     // classes, but we can't easily block the whole package because of
     // all our unit tests.
-    private static final Set<Class<?>> FORBIDDEN_TYPES = ImmutableSet.of(
+    private static final ImmutableSet<Class<?>> FORBIDDEN_TYPES =
+            ImmutableSet.<Class<?>>of(
                     AbstractModule.class,
                     Binder.class,
                     Binding.class,
@@ -37,11 +36,11 @@ abstract class AbstractBindingProcessor extends AbstractProcessor {
                     Stage.class,
                     TypeLiteral.class);
 
-    protected final ProcessedBindingData bindingData;
+    protected final ProcessedBindingData processedBindingData;
 
-    AbstractBindingProcessor(Errors errors, ProcessedBindingData bindingData) {
+    AbstractBindingProcessor(Errors errors, ProcessedBindingData processedBindingData) {
         super(errors);
-        this.bindingData = bindingData;
+        this.processedBindingData = processedBindingData;
     }
 
     protected <T> UntargettedBindingImpl<T> invalidBinding(
@@ -61,10 +60,10 @@ abstract class AbstractBindingProcessor extends AbstractProcessor {
         BindingImpl<?> original = injector.getExistingBinding(key);
         if (original != null) {
             // If it failed because of an explicit duplicate binding...
-            if (injector.state.getExplicitBinding(key) != null) {
+            if (injector.getBindingData().getExplicitBinding(key) != null) {
                 try {
-                    if (!isOkayDuplicate(original, binding, injector.state)) {
+                    if (!isOkayDuplicate(original, binding, injector.getBindingData())) {
-                        errors.bindingAlreadySet(key, original.getSource());
+                        errors.bindingAlreadySet(binding, original);
                         return;
                     }
                 } catch (Throwable t) {
@@ -80,27 +79,34 @@ abstract class AbstractBindingProcessor extends AbstractProcessor {
         }
 
         // prevent the parent from creating a JIT binding for this key
-        injector.state.parent().blacklist(key, injector.state, binding.getSource());
+        injector
-        injector.state.putBinding(key, binding);
+                .getJitBindingData()
+                .banKeyInParent(key, injector.getBindingData(), binding.getSource());
+        injector.getBindingData().putBinding(key, binding);
     }
 
     /**
-     * We tolerate duplicate bindings if one exposes the other or if the two bindings
+     * We tolerate duplicate bindings if one exposes the other or if the two bindings are considered
-     * are considered duplicates.
+     * duplicates (see {@link Bindings#areDuplicates(BindingImpl, BindingImpl)}.
      *
      * @param original the binding in the parent injector (candidate for an exposing binding)
      * @param binding the binding to check (candidate for the exposed binding)
      */
-    private boolean isOkayDuplicate(BindingImpl<?> original, BindingImpl<?> binding, State state) {
+    private static boolean isOkayDuplicate(
+            BindingImpl<?> original, BindingImpl<?> binding, InjectorBindingData bindingData) {
         if (original instanceof ExposedBindingImpl) {
-            ExposedBindingImpl<?> exposed = (ExposedBindingImpl) original;
+            ExposedBindingImpl<?> exposed = (ExposedBindingImpl<?>) original;
             InjectorImpl exposedFrom = (InjectorImpl) exposed.getPrivateElements().getInjector();
             return (exposedFrom == binding.getInjector());
         } else {
-            original = (BindingImpl<?>) state.getExplicitBindingsThisLevel().get(binding.getKey());
+            original = (BindingImpl<?>) bindingData.getExplicitBindingsThisLevel().get(binding.getKey());
             // If no original at this level, the original was on a parent, and we don't
             // allow deduplication between parents & children.
-            return original != null && original.equals(binding);
+            if (original == null) {
+                return false;
+            } else {
+                return original.equals(binding);
+            }
         }
     }
 
@@ -110,8 +116,8 @@ abstract class AbstractBindingProcessor extends AbstractProcessor {
     }
 
     /**
-     * Processor for visiting bindings.  Each overriden method that wants to
+     * Processor for visiting bindings. Each overriden method that wants to actually process the
-     * actually process the binding should call prepareBinding first.
+     * binding should call prepareBinding first.
      */
     abstract class Processor<T, V> extends DefaultBindingTargetVisitor<T, V> {
         final Object source;
@@ -136,7 +142,7 @@ abstract class AbstractBindingProcessor extends AbstractProcessor {
          * initialially processed.
          */
         protected void scheduleInitialization(BindingImpl<?> binding) {
-            bindingData.addUninitializedBinding(() -> initializeBinding(binding));
+            processedBindingData.addUninitializedBinding(() -> initializeBinding(binding));
         }
 
         /**
@@ -144,7 +150,7 @@ abstract class AbstractBindingProcessor extends AbstractProcessor {
          * bindings.
          */
         protected void scheduleDelayedInitialization(BindingImpl<?> binding) {
-            bindingData.addDelayedUninitializedBinding(() -> initializeBinding(binding));
+            processedBindingData.addDelayedUninitializedBinding(() -> initializeBinding(binding));
         }
 
         private void initializeBinding(BindingImpl<?> binding) {

src/main/java/com/google/inject/internal/Annotations.java

@@ -2,7 +2,6 @@ package com.google.inject.internal;
 
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
-import com.google.common.base.Function;
 import com.google.common.base.Joiner;
 import com.google.common.base.Joiner.MapJoiner;
 import com.google.common.base.Preconditions;
@@ -18,8 +17,6 @@ import com.google.inject.TypeLiteral;
 import com.google.inject.internal.util.Classes;
 import com.google.inject.name.Named;
 import com.google.inject.name.Names;
-
-import javax.inject.Qualifier;
 import java.lang.annotation.Annotation;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -30,40 +27,16 @@ import java.lang.reflect.Proxy;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Map;
+import javax.inject.Qualifier;
 
 /**
  * Annotation utilities.
  *
+ * @author crazybob@google.com (Bob Lee)
  */
 public class Annotations {
 
-    private static final MapJoiner JOINER = Joiner.on(", ").withKeyValueSeparator("=");
+    /** Returns {@code true} if the given annotation type has no attributes. */
-    private static final Function<Object, String> DEEP_TO_STRING_FN = new Function<Object, String>() {
-        @Override
-        public String apply(Object arg) {
-            String s = Arrays.deepToString(new Object[]{arg});
-            return s.substring(1, s.length() - 1); // cut off brackets
-        }
-    };
-
-    private static final LoadingCache<Class<? extends Annotation>, Annotation> cache =
-            CacheBuilder.newBuilder()
-                    .weakKeys()
-                    .build(new CacheLoader<>() {
-                        @Override
-                        public Annotation load(Class<? extends Annotation> input) {
-                            return generateAnnotationImpl(input);
-                        }
-                    });
-
-    private static final AnnotationChecker scopeChecker = new AnnotationChecker(
-            Arrays.asList(ScopeAnnotation.class, javax.inject.Scope.class));
-    private static final AnnotationChecker bindingAnnotationChecker = new AnnotationChecker(
-            Arrays.asList(BindingAnnotation.class, Qualifier.class));
-
-    /**
-     * Returns {@code true} if the given annotation type has no attributes.
-     */
     public static boolean isMarker(Class<? extends Annotation> annotationType) {
         return annotationType.getDeclaredMethods().length == 0;
     }
@@ -79,11 +52,22 @@ public class Annotations {
         return hasMethods;
     }
 
+    private static final LoadingCache<Class<? extends Annotation>, Annotation> cache =
+            CacheBuilder.newBuilder()
+                    .weakKeys()
+                    .build(
+                            new CacheLoader<Class<? extends Annotation>, Annotation>() {
+                                @Override
+                                public Annotation load(Class<? extends Annotation> input) {
+                                    return generateAnnotationImpl(input);
+                                }
+                            });
+
     /**
      * Generates an Annotation for the annotation class. Requires that the annotation is all
      * optionals.
      */
-    @SuppressWarnings("unchecked")
+    @SuppressWarnings("unchecked") // Safe because generateAnnotationImpl returns T for Class<T>
     public static <T extends Annotation> T generateAnnotation(Class<T> annotationType) {
         Preconditions.checkState(
                 isAllDefaultMethods(annotationType), "%s is not all default methods", annotationType);
@@ -92,23 +76,26 @@ public class Annotations {
 
     private static <T extends Annotation> T generateAnnotationImpl(final Class<T> annotationType) {
         final Map<String, Object> members = resolveMembers(annotationType);
-        return annotationType.cast(Proxy.newProxyInstance(
+        return annotationType.cast(
+                Proxy.newProxyInstance(
                         annotationType.getClassLoader(),
                         new Class<?>[] {annotationType},
-                (proxy, method, args) -> {
+                        new InvocationHandler() {
+                            @Override
+                            public Object invoke(Object proxy, Method method, Object[] args) throws Exception {
                                 String name = method.getName();
-                    switch (name) {
+                                if (name.equals("annotationType")) {
-                        case "annotationType":
                                     return annotationType;
-                        case "toString":
+                                } else if (name.equals("toString")) {
                                     return annotationToString(annotationType, members);
-                        case "hashCode":
+                                } else if (name.equals("hashCode")) {
                                     return annotationHashCode(annotationType, members);
-                        case "equals":
+                                } else if (name.equals("equals")) {
                                     return annotationEquals(annotationType, members, args[0]);
-                        default:
+                                } else {
                                     return members.get(name);
                                 }
+                            }
                         }));
     }
 
@@ -121,11 +108,10 @@ public class Annotations {
         return result.build();
     }
 
-    /**
+    /** Implements {@link Annotation#equals}. */
-     * Implements {@link Annotation#equals}.
+    private static boolean annotationEquals(
-     */
+            Class<? extends Annotation> type, Map<String, Object> members, Object other)
-    private static boolean annotationEquals(Class<? extends Annotation> type,
+            throws Exception {
-                                            Map<String, Object> members, Object other) throws Exception {
         if (!type.isInstance(other)) {
             return false;
         }
@@ -139,11 +125,9 @@ public class Annotations {
         return true;
     }
 
-    /**
+    /** Implements {@link Annotation#hashCode}. */
-     * Implements {@link Annotation#hashCode}.
+    private static int annotationHashCode(
-     */
+            Class<? extends Annotation> type, Map<String, Object> members) throws Exception {
-    private static int annotationHashCode(Class<? extends Annotation> type,
-                                          Map<String, Object> members) throws Exception {
         int result = 0;
         for (Method method : type.getDeclaredMethods()) {
             String name = method.getName();
@@ -153,36 +137,38 @@ public class Annotations {
         return result;
     }
 
-    /**
+    private static final MapJoiner JOINER = Joiner.on(", ").withKeyValueSeparator("=");
-     * Implements {@link Annotation#toString}.
+
-     */
+    /** Implements {@link Annotation#toString}. */
-    private static String annotationToString(Class<? extends Annotation> type,
+    private static String annotationToString(
-                                             Map<String, Object> members) throws Exception {
+            Class<? extends Annotation> type, Map<String, Object> members) throws Exception {
         StringBuilder sb = new StringBuilder().append("@").append(type.getName()).append("(");
-        JOINER.appendTo(sb, Maps.transformValues(members, DEEP_TO_STRING_FN));
+        JOINER.appendTo(
+                sb,
+                Maps.transformValues(
+                        members,
+                        arg -> {
+                            String s = Arrays.deepToString(new Object[] {arg});
+                            return s.substring(1, s.length() - 1); // cut off brackets
+                        }));
         return sb.append(")").toString();
     }
 
-    /**
+    /** Returns true if the given annotation is retained at runtime. */
-     * Returns true if the given annotation is retained at runtime.
-     */
     public static boolean isRetainedAtRuntime(Class<? extends Annotation> annotationType) {
         Retention retention = annotationType.getAnnotation(Retention.class);
         return retention != null && retention.value() == RetentionPolicy.RUNTIME;
     }
 
-    /**
+    /** Returns the scope annotation on {@code type}, or null if none is specified. */
-     * Returns the scope annotation on {@code type}, or null if none is specified.
-     */
     public static Class<? extends Annotation> findScopeAnnotation(
             Errors errors, Class<?> implementation) {
         return findScopeAnnotation(errors, implementation.getAnnotations());
     }
 
-    /**
+    /** Returns the scoping annotation, or null if there isn't one. */
-     * Returns the scoping annotation, or null if there isn't one.
+    public static Class<? extends Annotation> findScopeAnnotation(
-     */
+            Errors errors, Annotation[] annotations) {
-    public static Class<? extends Annotation> findScopeAnnotation(Errors errors, Annotation[] annotations) {
         Class<? extends Annotation> found = null;
 
         for (Annotation annotation : annotations) {
@@ -210,10 +196,50 @@ public class Annotations {
         return false;
     }
 
-    private static final boolean QUOTE_MEMBER_VALUES = determineWhetherToQuote();
+    private static class AnnotationToStringConfig {
+        final boolean quote;
+        final boolean includeMemberName;
 
+        AnnotationToStringConfig(boolean quote, boolean includeMemberName) {
+            this.quote = quote;
+            this.includeMemberName = includeMemberName;
+        }
+    }
+
+    private static final AnnotationToStringConfig ANNOTATION_TO_STRING_CONFIG =
+            determineAnnotationToStringConfig();
+
+    /**
+     * Returns {@code value}, quoted if annotation implementations quote their member values. In Java
+     * 9, annotations quote their string members.
+     */
     public static String memberValueString(String value) {
-        return QUOTE_MEMBER_VALUES ? "\"" + value + "\"" : value;
+        return ANNOTATION_TO_STRING_CONFIG.quote ? "\"" + value + "\"" : value;
+    }
+
+    /**
+     * Returns string representation of the annotation memeber.
+     *
+     * <p>The value of the member is prefixed with `memberName=` unless the runtime omits the member
+     * name. The value of the member is quoted if annotation implementations quote their member values
+     * and the value type is String.
+     *
+     * <p>In Java 9, annotations quote their string members and in Java 15, the member name is
+     * omitted.
+     */
+    public static String memberValueString(String memberName, Object value) {
+        StringBuilder sb = new StringBuilder();
+        boolean quote = ANNOTATION_TO_STRING_CONFIG.quote;
+        boolean includeMemberName = ANNOTATION_TO_STRING_CONFIG.includeMemberName;
+        if (includeMemberName) {
+            sb.append(memberName).append('=');
+        }
+        if (quote && (value instanceof String)) {
+            sb.append('"').append(value).append('"');
+        } else {
+            sb.append(value);
+        }
+        return sb.toString();
     }
 
     @Retention(RUNTIME)
@@ -221,26 +247,64 @@ public class Annotations {
         String value();
     }
 
-    @TestAnnotation("determineWhetherToQuote")
+    @TestAnnotation("determineAnnotationToStringConfig")
-    private static boolean determineWhetherToQuote() {
+    private static AnnotationToStringConfig determineAnnotationToStringConfig() {
         try {
-            String annotation = Annotations.class
+            String annotation =
-                            .getDeclaredMethod("determineWhetherToQuote")
+                    Annotations.class
+                            .getDeclaredMethod("determineAnnotationToStringConfig")
                             .getAnnotation(TestAnnotation.class)
                             .toString();
-            return annotation.contains("\"determineWhetherToQuote\"");
+            boolean quote = annotation.contains("\"determineAnnotationToStringConfig\"");
+            boolean includeMemberName = annotation.contains("value=");
+            return new AnnotationToStringConfig(quote, includeMemberName);
         } catch (NoSuchMethodException e) {
             throw new AssertionError(e);
         }
     }
 
+    /** Checks for the presence of annotations. Caches results because Android doesn't. */
+    static class AnnotationChecker {
+        private final Collection<Class<? extends Annotation>> annotationTypes;
+
+        /** Returns true if the given class has one of the desired annotations. */
+        private CacheLoader<Class<? extends Annotation>, Boolean> hasAnnotations =
+                new CacheLoader<Class<? extends Annotation>, Boolean>() {
+                    @Override
+                    public Boolean load(Class<? extends Annotation> annotationType) {
+                        for (Annotation annotation : annotationType.getAnnotations()) {
+                            if (annotationTypes.contains(annotation.annotationType())) {
+                                return true;
+                            }
+                        }
+                        return false;
+                    }
+                };
+
+        final LoadingCache<Class<? extends Annotation>, Boolean> cache =
+                CacheBuilder.newBuilder().weakKeys().build(hasAnnotations);
+
+        /** Constructs a new checker that looks for annotations of the given types. */
+        AnnotationChecker(Collection<Class<? extends Annotation>> annotationTypes) {
+            this.annotationTypes = annotationTypes;
+        }
+
+        /** Returns true if the given type has one of the desired annotations. */
+        boolean hasAnnotations(Class<? extends Annotation> annotated) {
+            return cache.getUnchecked(annotated);
+        }
+    }
+
+    private static final AnnotationChecker scopeChecker =
+            new AnnotationChecker(Arrays.asList(ScopeAnnotation.class, javax.inject.Scope.class));
+
     public static boolean isScopeAnnotation(Class<? extends Annotation> annotationType) {
         return scopeChecker.hasAnnotations(annotationType);
     }
 
     /**
-     * Adds an error if there is a misplaced annotations on {@code type}. Scoping
+     * Adds an error if there is a misplaced annotations on {@code type}. Scoping annotations are not
-     * annotations are not allowed on abstract classes or interfaces.
+     * allowed on abstract classes or interfaces.
      */
     public static void checkForMisplacedScopeAnnotations(
             Class<?> type, Object source, Errors errors) {
@@ -256,21 +320,22 @@ public class Annotations {
         }
     }
 
-    /**
+    // NOTE: getKey/findBindingAnnotation are used by Gin which is abandoned.  So changing this API
-     * Gets a key for the given type, member and annotations.
+    // will prevent Gin users from upgrading Guice version.
-     */
+
-    public static Key<?> getKey(TypeLiteral<?> type, Member member, Annotation[] annotations,
+    /** Gets a key for the given type, member and annotations. */
-                                Errors errors) throws ErrorsException {
+    public static Key<?> getKey(
+            TypeLiteral<?> type, Member member, Annotation[] annotations, Errors errors)
+            throws ErrorsException {
         int numErrorsBefore = errors.size();
         Annotation found = findBindingAnnotation(errors, member, annotations);
         errors.throwIfNewErrors(numErrorsBefore);
         return found == null ? Key.get(type) : Key.get(type, found);
     }
 
-    /**
+    /** Returns the binding annotation on {@code member}, or null if there isn't one. */
-     * Returns the binding annotation on {@code member}, or null if there isn't one.
+    public static Annotation findBindingAnnotation(
-     */
+            Errors errors, Member member, Annotation[] annotations) {
-    public static Annotation findBindingAnnotation(Errors errors, Member member, Annotation[] annotations) {
         Annotation found = null;
 
         for (Annotation annotation : annotations) {
@@ -287,9 +352,10 @@ public class Annotations {
         return found;
     }
 
-    /**
+    private static final AnnotationChecker bindingAnnotationChecker =
-     * Returns true if annotations of the specified type are binding annotations.
+            new AnnotationChecker(Arrays.asList(BindingAnnotation.class, Qualifier.class));
-     */
+
+    /** Returns true if annotations of the specified type are binding annotations. */
     public static boolean isBindingAnnotation(Class<? extends Annotation> annotationType) {
         return bindingAnnotationChecker.hasAnnotations(annotationType);
     }
@@ -336,44 +402,4 @@ public class Annotations {
             return "";
         }
     }
-
-    /**
-     * Checks for the presence of annotations. Caches results because Android doesn't.
-     */
-    static class AnnotationChecker {
-        private final Collection<Class<? extends Annotation>> annotationTypes;
-
-        /**
-         * Returns true if the given class has one of the desired annotations.
-         */
-        private CacheLoader<Class<? extends Annotation>, Boolean> hasAnnotations =
-                new CacheLoader<>() {
-                    @Override
-                    public Boolean load(Class<? extends Annotation> annotationType) {
-                        for (Annotation annotation : annotationType.getAnnotations()) {
-                            if (annotationTypes.contains(annotation.annotationType())) {
-                                return true;
-                            }
-                        }
-                        return false;
-                    }
-                };
-
-        final LoadingCache<Class<? extends Annotation>, Boolean> cache =
-                CacheBuilder.newBuilder().weakKeys().build(hasAnnotations);
-
-        /**
-         * Constructs a new checker that looks for annotations of the given types.
-         */
-        AnnotationChecker(Collection<Class<? extends Annotation>> annotationTypes) {
-            this.annotationTypes = annotationTypes;
-        }
-
-        /**
-         * Returns true if the given type has one of the desired annotations.
-         */
-        boolean hasAnnotations(Class<? extends Annotation> annotated) {
-            return cache.getUnchecked(annotated);
-        }
-    }
 }

src/main/java/com/google/inject/internal/BindingAlreadySetError.java

@@ -0,0 +1,52 @@
+package com.google.inject.internal;
+
+import com.google.common.collect.ImmutableList;
+import com.google.inject.Binding;
+import com.google.inject.spi.ErrorDetail;
+import java.util.ArrayList;
+import java.util.Formatter;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/** Error reported by Guice when a key is bound at multiple places the injector. */
+final class BindingAlreadySetError extends InternalErrorDetail<BindingAlreadySetError> {
+    private final Binding<?> binding;
+    private final Binding<?> original;
+
+    BindingAlreadySetError(Binding<?> binding, Binding<?> original, List<Object> sources) {
+        super(
+                ErrorId.BINDING_ALREADY_SET,
+                String.format("%s was bound multiple times.", Messages.convert(binding.getKey())),
+                sources,
+                null);
+        this.binding = binding;
+        this.original = original;
+    }
+
+    @Override
+    public boolean isMergeable(ErrorDetail<?> otherError) {
+        return otherError instanceof BindingAlreadySetError
+                && ((BindingAlreadySetError) otherError).binding.getKey().equals(binding.getKey());
+    }
+
+    @Override
+    public void formatDetail(List<ErrorDetail<?>> mergeableErrors, Formatter formatter) {
+        List<List<Object>> sourcesList = new ArrayList<>();
+        sourcesList.add(ImmutableList.of(original.getSource()));
+        sourcesList.add(ImmutableList.of(binding.getSource()));
+        sourcesList.addAll(
+                mergeableErrors.stream()
+                        .map(e -> ((BindingAlreadySetError) e).binding.getSource())
+                        .map(ImmutableList::of)
+                        .collect(Collectors.toList()));
+        formatter.format("%n%s%n", Messages.bold("Bound at:"));
+        for (int i = 0; i < sourcesList.size(); i++) {
+            ErrorFormatter.formatSources(i + 1, sourcesList.get(i), formatter);
+        }
+    }
+
+    @Override
+    public BindingAlreadySetError withSources(List<Object> newSources) {
+        return new BindingAlreadySetError(binding, original, newSources);
+    }
+}

src/main/java/com/google/inject/internal/BindingProcessor.java

@@ -15,7 +15,6 @@ import com.google.inject.spi.ProviderBinding;
 import com.google.inject.spi.ProviderInstanceBinding;
 import com.google.inject.spi.ProviderKeyBinding;
 import com.google.inject.spi.UntargettedBinding;
-
 import java.util.Set;
 
 /**
@@ -25,8 +24,9 @@ final class BindingProcessor extends AbstractBindingProcessor {
 
     private final Initializer initializer;
 
-    BindingProcessor(Errors errors, Initializer initializer, ProcessedBindingData bindingData) {
+    BindingProcessor(
-        super(errors, bindingData);
+            Errors errors, Initializer initializer, ProcessedBindingData processedBindingData) {
+        super(errors, processedBindingData);
         this.initializer = initializer;
     }
 
@@ -49,13 +49,22 @@ final class BindingProcessor extends AbstractBindingProcessor {
             return true;
         }
 
-        return command.acceptTargetVisitor(new Processor<>((BindingImpl<T>) command) {
+        return command.acceptTargetVisitor(
+                new Processor<T, Boolean>((BindingImpl<T>) command) {
                     @Override
                     public Boolean visit(ConstructorBinding<? extends T> binding) {
                         prepareBinding();
                         try {
-                    ConstructorBindingImpl<T> onInjector = ConstructorBindingImpl.create(injector, key,
+                            ConstructorBindingImpl<T> onInjector =
-                            binding.getConstructor(), source, scoping, errors, false, false);
+                                    ConstructorBindingImpl.create(
+                                            injector,
+                                            key,
+                                            binding.getConstructor(),
+                                            source,
+                                            scoping,
+                                            errors,
+                                            false,
+                                            false);
                             scheduleInitialization(onInjector);
                             putBinding(onInjector);
                         } catch (ErrorsException e) {
@@ -72,13 +81,15 @@ final class BindingProcessor extends AbstractBindingProcessor {
                         T instance = binding.getInstance();
                         @SuppressWarnings("unchecked") // safe to cast to binding<T> because
                         // the processor was constructed w/ it
-                Initializable<T> ref = initializer.requestInjection(
+                        Initializable<T> ref =
+                                initializer.requestInjection(
                                         injector, instance, (Binding<T>) binding, source, injectionPoints);
                         ConstantFactory<? extends T> factory = new ConstantFactory<>(ref);
                         InternalFactory<? extends T> scopedFactory =
                                 Scoping.scope(key, injector, factory, source, scoping);
-                putBinding(new InstanceBindingImpl<>(injector, key, source,
+                        putBinding(
-                        scopedFactory, injectionPoints, instance));
+                                new InstanceBindingImpl<T>(
+                                        injector, key, source, scopedFactory, injectionPoints, instance));
                         return true;
                     }
 
@@ -94,31 +105,46 @@ final class BindingProcessor extends AbstractBindingProcessor {
                         }
                         Set<InjectionPoint> injectionPoints = binding.getInjectionPoints();
                         Initializable<? extends javax.inject.Provider<? extends T>> initializable =
-                        initializer.requestInjection(injector, provider, null, source, injectionPoints);
+                                initializer.<javax.inject.Provider<? extends T>>requestInjection(
+                                        injector, provider, null, source, injectionPoints);
                         // always visited with Binding<T>
                         @SuppressWarnings("unchecked")
-                InternalFactory<T> factory = new InternalFactoryToInitializableAdapter<>(
+                        InternalFactory<T> factory =
-                        initializable, source,
+                                new InternalFactoryToInitializableAdapter<T>(
+                                        initializable,
+                                        source,
                                         injector.provisionListenerStore.get((ProviderInstanceBinding<T>) binding));
-                InternalFactory<? extends T> scopedFactory = Scoping.scope(key, injector, factory, source, scoping);
+                        InternalFactory<? extends T> scopedFactory =
-                putBinding(new ProviderInstanceBindingImpl<>(injector, key, source, scopedFactory, scoping,
+                                Scoping.scope(key, injector, factory, source, scoping);
-                        provider, injectionPoints));
+                        putBinding(
+                                new ProviderInstanceBindingImpl<T>(
+                                        injector, key, source, scopedFactory, scoping, provider, injectionPoints));
                         return true;
                     }
 
                     @Override
                     public Boolean visit(ProviderKeyBinding<? extends T> binding) {
                         prepareBinding();
-                Key<? extends javax.inject.Provider<? extends T>> providerKey = binding.getProviderKey();
+                        Key<? extends javax.inject.Provider<? extends T>> providerKey =
+                                binding.getProviderKey();
                         // always visited with Binding<T>
                         @SuppressWarnings("unchecked")
-                BoundProviderFactory<T> boundProviderFactory = new BoundProviderFactory<>(
+                        BoundProviderFactory<T> boundProviderFactory =
-                        injector, providerKey, source,
+                                new BoundProviderFactory<T>(
+                                        injector,
+                                        providerKey,
+                                        source,
                                         injector.provisionListenerStore.get((ProviderKeyBinding<T>) binding));
-                bindingData.addCreationListener(boundProviderFactory);
+                        processedBindingData.addCreationListener(boundProviderFactory);
-                InternalFactory<? extends T> scopedFactory = Scoping.scope(
+                        InternalFactory<? extends T> scopedFactory =
-                        key, injector, boundProviderFactory, source, scoping);
+                                Scoping.scope(
-                putBinding(new LinkedProviderBindingImpl<>(
+                                        key,
+                                        injector,
+                                        (InternalFactory<? extends T>) boundProviderFactory,
+                                        source,
+                                        scoping);
+                        putBinding(
+                                new LinkedProviderBindingImpl<T>(
                                         injector, key, source, scopedFactory, scoping, providerKey));
                         return true;
                     }
@@ -128,13 +154,16 @@ final class BindingProcessor extends AbstractBindingProcessor {
                         prepareBinding();
                         Key<? extends T> linkedKey = binding.getLinkedKey();
                         if (key.equals(linkedKey)) {
-                    errors.recursiveBinding();
+                            // TODO: b/168656899 check for transitive recursive binding
+                            errors.recursiveBinding(key, linkedKey);
                         }
+
                         FactoryProxy<T> factory = new FactoryProxy<>(injector, key, linkedKey, source);
-                bindingData.addCreationListener(factory);
+                        processedBindingData.addCreationListener(factory);
                         InternalFactory<? extends T> scopedFactory =
                                 Scoping.scope(key, injector, factory, source, scoping);
-                putBinding(new LinkedBindingImpl<>(injector, key, source, scopedFactory, scoping, linkedKey));
+                        putBinding(
+                                new LinkedBindingImpl<T>(injector, key, source, scopedFactory, scoping, linkedKey));
                         return true;
                     }
 
@@ -142,7 +171,7 @@ final class BindingProcessor extends AbstractBindingProcessor {
                     private Boolean visitInternalProviderInstanceBindingFactory(
                             InternalProviderInstanceBindingImpl.Factory<T> provider) {
                         InternalProviderInstanceBindingImpl<T> binding =
-                        new InternalProviderInstanceBindingImpl<>(
+                                new InternalProviderInstanceBindingImpl<T>(
                                         injector,
                                         key,
                                         source,
@@ -200,8 +229,13 @@ final class BindingProcessor extends AbstractBindingProcessor {
 
     private <T> void bindExposed(PrivateElements privateElements, Key<T> key) {
         ExposedKeyFactory<T> exposedKeyFactory = new ExposedKeyFactory<>(key, privateElements);
-        bindingData.addCreationListener(exposedKeyFactory);
+        processedBindingData.addCreationListener(exposedKeyFactory);
-        putBinding(new ExposedBindingImpl<>(
+        putBinding(
-                injector, privateElements.getExposedSource(key), key, exposedKeyFactory, privateElements));
+                new ExposedBindingImpl<T>(
+                        injector,
+                        privateElements.getExposedSource(key),
+                        key,
+                        exposedKeyFactory,
+                        privateElements));
     }
 }

src/main/java/com/google/inject/internal/ChildBindingAlreadySetError.java

@@ -0,0 +1,85 @@
+package com.google.inject.internal;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Streams;
+import com.google.inject.Key;
+import com.google.inject.spi.ErrorDetail;
+import java.util.ArrayList;
+import java.util.Formatter;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Error reported by Guice when a key is already bound in one or more child injectors or private
+ * modules.
+ */
+final class ChildBindingAlreadySetError extends InternalErrorDetail<ChildBindingAlreadySetError> {
+    private final Key<?> key;
+    private final ImmutableList<Object> existingSources;
+
+    ChildBindingAlreadySetError(Key<?> key, Iterable<Object> existingSoruces, List<Object> sources) {
+        super(
+                ErrorId.CHILD_BINDING_ALREADY_SET,
+                String.format(
+                        "Unable to create binding for %s because it was already configured on one or more"
+                                + " child injectors or private modules.",
+                        Messages.convert(key)),
+                sources,
+                null);
+        this.key = key;
+        // Can't use ImmutableList.toImmutableList here because of b/156759807.
+        this.existingSources =
+                ImmutableList.copyOf(
+                        Streams.stream(existingSoruces)
+                                .map(source -> source == null ? "" : source)
+                                .collect(Collectors.toList()));
+    }
+
+    @Override
+    public boolean isMergeable(ErrorDetail<?> otherError) {
+        return otherError instanceof ChildBindingAlreadySetError
+                && ((ChildBindingAlreadySetError) otherError).key.equals(this.key);
+    }
+
+    @Override
+    public void formatDetail(List<ErrorDetail<?>> mergeableErrors, Formatter formatter) {
+        formatter.format("%n%s%n", Messages.bold("Bound at:"));
+        int index = 1;
+        for (Object source : existingSources) {
+            formatter.format("%-2s: ", index++);
+            if (source.equals("")) {
+                formatter.format("as a just-in-time binding%n");
+            } else {
+                new SourceFormatter(source, formatter, /* omitPreposition= */ true).format();
+            }
+        }
+        List<List<Object>> sourcesList = new ArrayList<>();
+        sourcesList.add(getSources());
+        mergeableErrors.forEach(error -> sourcesList.add(error.getSources()));
+
+        List<List<Object>> filteredSources =
+                sourcesList.stream()
+                        .map(this::trimSource)
+                        .filter(list -> !list.isEmpty())
+                        .collect(Collectors.toList());
+        if (!filteredSources.isEmpty()) {
+            formatter.format("%n%s%n", Messages.bold("Requested by:"));
+            for (int i = 0; i < sourcesList.size(); i++) {
+                ErrorFormatter.formatSources(i + 1, sourcesList.get(i), formatter);
+            }
+        }
+
+        // TODO(b/151482394): Detect if the key was bound in any PrivateModule and suggest exposing the
+        // key in those cases.
+    }
+
+    @Override
+    public ChildBindingAlreadySetError withSources(List<Object> newSources) {
+        return new ChildBindingAlreadySetError(key, existingSources, newSources);
+    }
+
+    /** Omit the key itself in the source list since the information is redundant. */
+    private List<Object> trimSource(List<Object> sources) {
+        return sources.stream().filter(source -> !source.equals(this.key)).collect(Collectors.toList());
+    }
+}

src/main/java/com/google/inject/internal/ConstructorBindingImpl.java

@@ -1,11 +1,15 @@
 package com.google.inject.internal;
 
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.inject.internal.Annotations.findScopeAnnotation;
+import static com.google.inject.internal.GuiceInternal.GUICE_INTERNAL;
+import static com.google.inject.spi.Elements.withTrustedSource;
+
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
 import com.google.common.collect.ImmutableSet;
 import com.google.inject.Binder;
 import com.google.inject.ConfigurationException;
-import com.google.inject.Inject;
 import com.google.inject.Key;
 import com.google.inject.TypeLiteral;
 import com.google.inject.internal.util.Classes;
@@ -13,23 +17,19 @@ import com.google.inject.spi.BindingTargetVisitor;
 import com.google.inject.spi.ConstructorBinding;
 import com.google.inject.spi.Dependency;
 import com.google.inject.spi.InjectionPoint;
-
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Modifier;
 import java.util.Set;
 
-import static com.google.common.base.Preconditions.checkState;
-import static com.google.inject.internal.Annotations.findScopeAnnotation;
-
 final class ConstructorBindingImpl<T> extends BindingImpl<T>
         implements ConstructorBinding<T>, DelayedInitialize {
 
     private final Factory<T> factory;
-
     private final InjectionPoint constructorInjectionPoint;
 
-    private ConstructorBindingImpl(InjectorImpl injector,
+    private ConstructorBindingImpl(
+            InjectorImpl injector,
             Key<T> key,
             Object source,
             InternalFactory<? extends T> scopedFactory,
@@ -41,35 +41,42 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
         this.constructorInjectionPoint = constructorInjectionPoint;
     }
 
-    public ConstructorBindingImpl(Key<T> key, Object source, Scoping scoping,
+    public ConstructorBindingImpl(
-                                  InjectionPoint constructorInjectionPoint, Set<InjectionPoint> injectionPoints) {
+            Key<T> key,
+            Object source,
+            Scoping scoping,
+            InjectionPoint constructorInjectionPoint,
+            Set<InjectionPoint> injectionPoints) {
         super(source, key, scoping);
-        this.factory = new Factory<T>(false, key);
+        this.factory = new Factory<>(false, key);
-        ConstructionProxy<T> constructionProxy
+        ConstructionProxy<T> constructionProxy =
-                = new DefaultConstructionProxyFactory<T>(constructorInjectionPoint).create();
+                new DefaultConstructionProxyFactory<T>(constructorInjectionPoint).create();
         this.constructorInjectionPoint = constructorInjectionPoint;
-        factory.constructorInjector = new ConstructorInjector<T>(
+        factory.constructorInjector =
-                injectionPoints, constructionProxy, null, null);
+                new ConstructorInjector<T>(injectionPoints, constructionProxy, null, null);
     }
 
     /**
      * @param constructorInjector the constructor to use, or {@code null} to use the default.
-     * @param failIfNotLinked     true if this ConstructorBindingImpl's InternalFactory should
+     * @param failIfNotLinked true if this ConstructorBindingImpl's InternalFactory should only
-     *                            only succeed if retrieved from a linked binding
+     *     succeed if retrieved from a linked binding
      */
-    static <T> ConstructorBindingImpl<T> create(InjectorImpl injector, Key<T> key,
+    static <T> ConstructorBindingImpl<T> create(
+            InjectorImpl injector,
+            Key<T> key,
             InjectionPoint constructorInjector,
             Object source,
             Scoping scoping,
             Errors errors,
-                                                boolean failIfNotLinked, boolean failIfNotExplicit)
+            boolean failIfNotLinked,
+            boolean atInjectRequired)
             throws ErrorsException {
         int numErrors = errors.size();
 
-        @SuppressWarnings("unchecked") // constructorBinding guarantees type is consistent
+        Class<?> rawType =
-                Class<? super T> rawType = constructorInjector == null
+                constructorInjector == null
                         ? key.getTypeLiteral().getRawType()
-                : (Class) constructorInjector.getDeclaringType().getRawType();
+                        : constructorInjector.getDeclaringType().getRawType();
 
         // We can't inject abstract classes.
         if (Modifier.isAbstract(rawType.getModifiers())) {
@@ -86,10 +93,8 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
         // Find a constructor annotated @Inject
         if (constructorInjector == null) {
             try {
-                constructorInjector = InjectionPoint.forConstructorOf(key.getTypeLiteral());
+                constructorInjector =
-                if (failIfNotExplicit && !hasAtInject((Constructor) constructorInjector.getMember())) {
+                        InjectionPoint.forConstructorOf(key.getTypeLiteral(), atInjectRequired);
-                    errors.atInjectRequired(rawType);
-                }
             } catch (ConfigurationException e) {
                 throw errors.merge(e.getErrorMessages()).toException();
             }
@@ -100,47 +105,36 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
             Class<?> annotatedType = constructorInjector.getMember().getDeclaringClass();
             Class<? extends Annotation> scopeAnnotation = findScopeAnnotation(errors, annotatedType);
             if (scopeAnnotation != null) {
-                scoping = Scoping.makeInjectable(Scoping.forAnnotation(scopeAnnotation),
+                scoping =
-                        injector, errors.withSource(rawType));
+                        Scoping.makeInjectable(
+                                Scoping.forAnnotation(scopeAnnotation), injector, errors.withSource(rawType));
             }
         }
 
         errors.throwIfNewErrors(numErrors);
 
-        Factory<T> factoryFactory = new Factory<T>(failIfNotLinked, key);
+        Factory<T> factoryFactory = new Factory<>(failIfNotLinked, key);
-        InternalFactory<? extends T> scopedFactory
+        InternalFactory<? extends T> scopedFactory =
-                = Scoping.scope(key, injector, factoryFactory, source, scoping);
+                Scoping.scope(key, injector, factoryFactory, source, scoping);
 
         return new ConstructorBindingImpl<T>(
                 injector, key, source, scopedFactory, scoping, factoryFactory, constructorInjector);
     }
 
-    /**
+    @Override
-     * Returns true if the inject annotation is on the constructor.
-     */
-    private static boolean hasAtInject(Constructor<?> cxtor) {
-        return cxtor.isAnnotationPresent(Inject.class)
-                || cxtor.isAnnotationPresent(javax.inject.Inject.class);
-    }
-
     @SuppressWarnings("unchecked") // the result type always agrees with the ConstructorInjector type
     public void initialize(InjectorImpl injector, Errors errors) throws ErrorsException {
         factory.constructorInjector =
                 (ConstructorInjector<T>) injector.constructors.get(constructorInjectionPoint, errors);
-        factory.provisionCallback =
+        factory.provisionCallback = injector.provisionListenerStore.get(this);
-                injector.provisionListenerStore.get(this);
     }
 
-    /**
+    /** True if this binding has been initialized and is ready for use. */
-     * True if this binding has been initialized and is ready for use.
-     */
     boolean isInitialized() {
         return factory.constructorInjector != null;
     }
 
-    /**
+    /** Returns an injection point that can be used to clean up the constructor store. */
-     * Returns an injection point that can be used to clean up the constructor store.
-     */
     InjectionPoint getInternalConstructor() {
         if (factory.constructorInjector != null) {
             return factory.constructorInjector.getConstructionProxy().getInjectionPoint();
@@ -149,22 +143,21 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
         }
     }
 
-    /**
+    /** Returns a set of dependencies that can be iterated over to clean up stray JIT bindings. */
-     * Returns a set of dependencies that can be iterated over to clean up stray JIT bindings.
-     */
     Set<Dependency<?>> getInternalDependencies() {
         ImmutableSet.Builder<InjectionPoint> builder = ImmutableSet.builder();
         if (factory.constructorInjector == null) {
             builder.add(constructorInjectionPoint);
-            // If the below throws, it's OK -- we just ignore those dependencies, because no one
-            // could have used them anyway.
             try {
-                builder.addAll(InjectionPoint.forInstanceMethodsAndFields(constructorInjectionPoint.getDeclaringType()));
+                builder.addAll(
+                        InjectionPoint.forInstanceMethodsAndFields(
+                                constructorInjectionPoint.getDeclaringType()));
             } catch (ConfigurationException ignored) {
+                // This is OK -- we just ignore those dependencies, because no one could have used them
+                // anyway.
             }
         } else {
-            builder.add(getConstructor())
+            builder.add(getConstructor()).addAll(getInjectableMembers());
-                    .addAll(getInjectableMembers());
         }
 
         return Dependency.forInjectionPoints(builder.build());
@@ -190,7 +183,8 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
 
     @Override
     public Set<Dependency<?>> getDependencies() {
-        return Dependency.forInjectionPoints(new ImmutableSet.Builder<InjectionPoint>()
+        return Dependency.forInjectionPoints(
+                new ImmutableSet.Builder<InjectionPoint>()
                         .add(getConstructor())
                         .addAll(getInjectableMembers())
                         .build());
@@ -208,11 +202,17 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
                 null, key, getSource(), factory, getScoping(), factory, constructorInjectionPoint);
     }
 
+    @Override
     @SuppressWarnings("unchecked") // the raw constructor member and declaring type always agree
     public void applyTo(Binder binder) {
         InjectionPoint constructor = getConstructor();
-        getScoping().applyTo(binder.withSource(getSource()).bind(getKey()).toConstructor(
+        getScoping()
-                (Constructor) getConstructor().getMember(), (TypeLiteral) constructor.getDeclaringType()));
+                .applyTo(
+                        withTrustedSource(GUICE_INTERNAL, binder, getSource())
+                                .bind(getKey())
+                                .toConstructor(
+                                        (Constructor) getConstructor().getMember(),
+                                        (TypeLiteral) constructor.getDeclaringType()));
     }
 
     @Override
@@ -252,6 +252,7 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
             this.key = key;
         }
 
+        @Override
         @SuppressWarnings("unchecked")
         public T get(InternalContext context, Dependency<?> dependency, boolean linked)
                 throws InternalProvisionException {
@@ -259,6 +260,7 @@ final class ConstructorBindingImpl<T> extends BindingImpl<T>
             if (localInjector == null) {
                 throw new IllegalStateException("Constructor not ready");
             }
+
             if (!linked && failIfNotLinked) {
                 throw InternalProvisionException.jitDisabled(key);
             }

src/main/java/com/google/inject/internal/DuplicateElementError.java

@@ -0,0 +1,127 @@
+package com.google.inject.internal;
+
+import com.google.common.collect.ImmutableMultimap;
+import com.google.inject.Binding;
+import com.google.inject.Key;
+import com.google.inject.spi.Dependency;
+import com.google.inject.spi.ErrorDetail;
+import java.util.Collection;
+import java.util.Formatter;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/**
+ * Error reported by Guice when duplicate elements are found in a {@link Multibinder} that does not
+ * permit duplicates.
+ */
+final class DuplicateElementError<T> extends InternalErrorDetail<DuplicateElementError<T>> {
+    private final Key<Set<T>> setKey;
+    private final ImmutableMultimap<T, Element<T>> elements;
+
+    DuplicateElementError(
+            Key<Set<T>> setKey, List<Binding<T>> bindings, T[] values, List<Object> sources) {
+        this(setKey, indexElements(bindings, values), sources);
+    }
+
+    private DuplicateElementError(
+            Key<Set<T>> setKey, ImmutableMultimap<T, Element<T>> elements, List<Object> sources) {
+        super(
+                ErrorId.DUPLICATE_ELEMENT,
+                String.format("Duplicate elements found in Multibinder %s.", Messages.convert(setKey)),
+                sources,
+                null);
+        this.setKey = setKey;
+        this.elements = elements;
+    }
+
+    @Override
+    protected void formatDetail(List<ErrorDetail<?>> others, Formatter formatter) {
+        formatter.format("%n%s%n", Messages.bold("Duplicates:"));
+        int duplicateIndex = 1;
+        for (Map.Entry<T, Collection<Element<T>>> entry : elements.asMap().entrySet()) {
+            formatter.format("%-2s: ", duplicateIndex++);
+            if (entry.getValue().size() > 1) {
+                Set<String> valuesAsString =
+                        entry.getValue().stream()
+                                .map(element -> element.value.toString())
+                                .collect(Collectors.toSet());
+                if (valuesAsString.size() == 1) {
+                    // String representation of the duplicates elements are the same, so only print out one.
+                    formatter.format("Element: %s%n", Messages.redBold(valuesAsString.iterator().next()));
+                    formatter.format("    Bound at:%n");
+                    int index = 1;
+                    for (Element<T> element : entry.getValue()) {
+                        formatter.format("    %-2s: ", index++);
+                        formatElement(element, formatter);
+                    }
+                } else {
+                    // Print out all elements as string when there are different string representations of the
+                    // elements. To keep the logic simple, same strings are not grouped together unless all
+                    // elements have the same string represnetation. This means some strings may be printed
+                    // out multiple times.
+                    // There is no indentation for the first duplicate element.
+                    boolean indent = false;
+                    for (Element<T> element : entry.getValue()) {
+                        if (indent) {
+                            formatter.format("    ");
+                        } else {
+                            indent = true;
+                        }
+                        formatter.format("Element: %s%n", Messages.redBold(element.value.toString()));
+                        formatter.format("    Bound at: ");
+                        formatElement(element, formatter);
+                    }
+                }
+            }
+        }
+        formatter.format("%n%s%n", Messages.bold("Multibinder declared at:"));
+        // Multibinder source includes the key of the set. Filter it out since it's not useful in the
+        // printed error stack.
+        List<Object> filteredSource =
+                getSources().stream()
+                        .filter(
+                                source -> {
+                                    if (source instanceof Dependency) {
+                                        return !((Dependency<?>) source).getKey().equals(setKey);
+                                    }
+                                    return true;
+                                })
+                        .collect(Collectors.toList());
+        ErrorFormatter.formatSources(filteredSource, formatter);
+    }
+
+    private void formatElement(Element<T> element, Formatter formatter) {
+        Object source = element.binding.getSource();
+        new SourceFormatter(
+                source,
+                formatter,
+                /** omitPreposition= */
+                true)
+                .format();
+    }
+
+    @Override
+    public DuplicateElementError<T> withSources(List<Object> newSources) {
+        return new DuplicateElementError<>(setKey, elements, newSources);
+    }
+
+    static <T> ImmutableMultimap<T, Element<T>> indexElements(List<Binding<T>> bindings, T[] values) {
+        ImmutableMultimap.Builder<T, Element<T>> map = ImmutableMultimap.builder();
+        for (int i = 0; i < values.length; i++) {
+            map.put(values[i], new Element<T>(values[i], bindings.get(i)));
+        }
+        return map.build();
+    }
+
+    static class Element<T> {
+        T value;
+        Binding<T> binding;
+
+        Element(T value, Binding<T> binding) {
+            this.value = value;
+            this.binding = binding;
+        }
+    }
+}

src/main/java/com/google/inject/internal/DuplicateMapKeyError.java

@@ -0,0 +1,70 @@
+package com.google.inject.internal;
+
+import com.google.common.collect.Multimap;
+import com.google.inject.Binding;
+import com.google.inject.Key;
+import com.google.inject.spi.ErrorDetail;
+import java.util.Collection;
+import java.util.Formatter;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Error reported by Guice when a duplicate key is found in a {@link MapBinder} that does not permit
+ * duplicates.
+ */
+final class DuplicateMapKeyError<K, V> extends InternalErrorDetail<DuplicateMapKeyError<K, V>> {
+    private final Key<Map<K, V>> mapKey;
+    private final Multimap<K, Binding<V>> duplicates;
+
+    DuplicateMapKeyError(
+            Key<Map<K, V>> mapKey, Multimap<K, Binding<V>> duplicates, List<Object> sources) {
+        super(ErrorId.DUPLICATE_MAP_KEY, getDuplicateKeysMessage(mapKey, duplicates), sources, null);
+        this.mapKey = mapKey;
+        this.duplicates = duplicates;
+    }
+
+    @Override
+    protected final void formatDetail(List<ErrorDetail<?>> others, Formatter formatter) {
+        formatter.format("%n%s%n", Messages.bold("Duplicates:"));
+
+        for (Map.Entry<K, Collection<Binding<V>>> entry : duplicates.asMap().entrySet()) {
+            formatter.format("  Key: \"%s\"%n", Messages.redBold(entry.getKey().toString()));
+            formatter.format("  Bound at:%n");
+            int index = 1;
+            for (Binding<V> binding : entry.getValue()) {
+                formatter.format("    %-2s: ", index++);
+                new SourceFormatter(
+                        binding.getSource(),
+                        formatter,
+                        /** omitPreposition= */
+                        true)
+                        .format();
+            }
+            formatter.format("%n");
+        }
+
+        formatter.format("%s%n", Messages.bold("MapBinder declared at:"));
+        ErrorFormatter.formatSources(getSources(), formatter);
+    }
+
+    @Override
+    public DuplicateMapKeyError<K, V> withSources(List<Object> newSources) {
+        return new DuplicateMapKeyError<>(mapKey, duplicates, newSources);
+    }
+
+    private static <K, V> String getDuplicateKeysMessage(
+            Key<Map<K, V>> mapKey, Multimap<K, Binding<V>> duplicates) {
+        Set<K> duplicateKeys = duplicates.keySet();
+        String mapBinderKey = Messages.convert(mapKey).toString();
+        String firstDuplicateKey = duplicateKeys.iterator().next().toString();
+        if (duplicateKeys.size() == 1) {
+            return String.format("Duplicate key \"%s\" found in %s.", firstDuplicateKey, mapBinderKey);
+        } else {
+            return String.format(
+                    "\"%s\" and %s other duplicate keys found in %s.",
+                    firstDuplicateKey, duplicateKeys.size() - 1, mapBinderKey);
+        }
+    }
+}

src/main/java/com/google/inject/internal/ErrorFormatter.java

@@ -0,0 +1,33 @@
+package com.google.inject.internal;
+
+import java.util.Formatter;
+import java.util.List;
+
+/** Helper for formatting Guice errors. */
+final class ErrorFormatter {
+    private ErrorFormatter() {}
+
+    /**
+     * Format a list of sources to the given {@code formatter}, prefixed by the give {@code index}.
+     */
+    static void formatSources(int index, List<Object> sources, Formatter formatter) {
+        for (int i = 0; i < sources.size(); i++) {
+            Object source = sources.get(i);
+            if (i == 0) {
+                formatter.format("%-3s: ", index);
+            } else {
+                formatter.format(SourceFormatter.INDENT);
+            }
+            new SourceFormatter(source, formatter, i == 0).format();
+        }
+    }
+
+    /** Format a list of sources to the given {@code formatter}. */
+    static void formatSources(List<Object> sources, Formatter formatter) {
+        for (int i = 0; i < sources.size(); i++) {
+            Object source = sources.get(i);
+            formatter.format("  ");
+            new SourceFormatter(source, formatter, i == 0).format();
+        }
+    }
+}

src/main/java/com/google/inject/internal/ErrorId.java

@@ -0,0 +1,65 @@
+package com.google.inject.internal;
+
+/** Enum used to identify a specific Guice error. */
+public enum ErrorId {
+    AMBIGUOUS_TYPE_CONVERSION,
+    AOP_DISABLED,
+    AT_INJECT_REQUIRED,
+    AT_TARGET_IS_MISSING_PARAMETER,
+    BINDING_ALREADY_SET,
+    BINDING_TO_GUICE_TYPE,
+    BINDING_TO_PROVIDER,
+    CAN_NOT_PROXY_CLASS,
+    CHILD_BINDING_ALREADY_SET,
+    CIRCULAR_PROXY_DISABLED,
+    CONSTRUCTOR_NOT_DEFINED_BY_TYPE,
+    CONVERSION_TYPE_ERROR,
+    CONVERTER_RETURNED_NULL,
+    DUPLICATE_BINDING_ANNOTATIONS,
+    DUPLICATE_ELEMENT,
+    DUPLICATE_MAP_KEY,
+    DUPLICATE_SCOPES,
+    DUPLICATE_SCOPE_ANNOTATIONS,
+    ERROR_ENHANCING_CLASS,
+    ERROR_INJECTING_CONSTRUCTOR,
+    ERROR_INJECTING_METHOD,
+    ERROR_IN_CUSTOM_PROVIDER,
+    ERROR_IN_USER_CODE,
+    ERROR_IN_USER_INJECTOR,
+    ERROR_NOTIFYING_TYPE_LISTENER,
+    EXPOSED_BUT_NOT_BOUND,
+    INJECT_ABSTRACT_METHOD,
+    INJECT_FINAL_FIELD,
+    INJECT_INNER_CLASS,
+    INJECT_METHOD_WITH_TYPE_PARAMETER,
+    INJECT_RAW_MEMBERS_INJECTOR,
+    INJECT_RAW_PROVIDER,
+    INJECT_RAW_TYPE_LITERAL,
+    JIT_BINDING_ALREADY_SET,
+    JIT_DISABLED,
+    JIT_DISABLED_IN_PARENT,
+    KEY_NOT_FULLY_SPECIFIED,
+    MISPLACED_BINDING_ANNOTATION,
+    MISSING_CONSTANT_VALUES,
+    MISSING_CONSTRUCTOR,
+    MISSING_IMPLEMENTATION,
+    MISSING_RUNTIME_RETENTION,
+    MISSING_SCOPE_ANNOTATION,
+    NOT_A_SUBTYPE,
+    NULL_ELEMENT_IN_SET,
+    NULL_INJECTED_INTO_NON_NULLABLE,
+    NULL_VALUE_IN_MAP,
+    OPTIONAL_CONSTRUCTOR,
+    RECURSIVE_BINDING,
+    RECURSIVE_IMPLEMENTATION_TYPE,
+    RECURSIVE_PROVIDER_TYPE,
+    SCOPE_ANNOTATION_ON_ABSTRACT_TYPE,
+    SCOPE_NOT_FOUND,
+    STATIC_INJECTION_ON_INTERFACE,
+    SUBTYPE_NOT_PROVIDED,
+    TOO_MANY_CONSTRUCTORS,
+    VOID_PROVIDER_METHOD,
+
+    // All other uncommon type of errors
+    OTHER;
+}

src/main/java/com/google/inject/internal/Errors.java

@@ -1,10 +1,11 @@
 package com.google.inject.internal;
 
+
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
+import com.google.common.collect.Multimap;
 import com.google.common.collect.Ordering;
-import com.google.common.primitives.Primitives;
 import com.google.inject.Binding;
 import com.google.inject.ConfigurationException;
 import com.google.inject.CreationException;
@@ -14,18 +15,18 @@ import com.google.inject.ProvisionException;
 import com.google.inject.Scope;
 import com.google.inject.TypeLiteral;
 import com.google.inject.internal.util.SourceProvider;
+import com.google.inject.spi.ElementSource;
 import com.google.inject.spi.Message;
 import com.google.inject.spi.ScopeBinding;
 import com.google.inject.spi.TypeConverterBinding;
 import com.google.inject.spi.TypeListenerBinding;
-
+import java.io.Serializable;
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
 import java.lang.reflect.Type;
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Formatter;
 import java.util.List;
@@ -45,36 +46,35 @@ import java.util.Set;
  * identify that method. When calling a method that's defined in a different context, call that
  * method with an errors object that includes its context.
  *
+ * @author jessewilson@google.com (Jesse Wilson)
  */
-public final class Errors {
+public final class Errors implements Serializable {
 
-    /** When a binding is not found, show at most this many bindings with the same type */
-    private static final int MAX_MATCHING_TYPES_REPORTED = 3;
-
-    /** When a binding is not found, show at most this many bindings that have some similarities */
-    private static final int MAX_RELATED_TYPES_REPORTED = 3;
 
+    /**
+     * Throws a ConfigurationException with an NullPointerExceptions as the cause if the given
+     * reference is {@code null}.
+     */
     static <T> T checkNotNull(T reference, String name) {
         if (reference != null) {
             return reference;
         }
+
         NullPointerException npe = new NullPointerException(name);
         throw new ConfigurationException(ImmutableSet.of(new Message(npe.toString(), npe)));
     }
 
+    /**
+     * Throws a ConfigurationException with a formatted {@link Message} if this condition is {@code
+     * false}.
+     */
     static void checkConfiguration(boolean condition, String format, Object... args) {
         if (condition) {
             return;
         }
-        throw new ConfigurationException(ImmutableSet.of(new Message(Messages.format(format, args))));
-    }
 
-    private static final ImmutableSet<Class<?>> COMMON_AMBIGUOUS_TYPES =
+        throw new ConfigurationException(ImmutableSet.of(new Message(Errors.format(format, args))));
-            ImmutableSet.<Class<?>>builder()
+    }
-                    .add(Object.class)
-                    .add(String.class)
-                    .addAll(Primitives.allWrapperTypes())
-                    .build();
 
     /** The root errors object. Used to access the list of error messages. */
     private final Errors root;
@@ -82,13 +82,10 @@ public final class Errors {
     /** The parent errors object. Used to obtain the chain of source objects. */
     private final Errors parent;
 
-    /**
+    /** The leaf source for errors added here. */
-     * The leaf source for errors added here.
-     */
     private final Object source;
-    /**
+
-     * null unless (root == this) and error messages exist. Never an empty list.
+    /** null unless (root == this) and error messages exist. Never an empty list. */
-     */
     private List<Message> errors; // lazy, use getErrorsForAdd()
 
     public Errors() {
@@ -116,305 +113,380 @@ public final class Errors {
                 : new Errors(this, source);
     }
 
+    /**
+     * We use a fairly generic error message here. The motivation is to share the same message for
+     * both bind time errors:
+     *
+     * <pre><code>Guice.createInjector(new AbstractModule() {
+     *   public void configure() {
+     *     bind(Runnable.class);
+     *   }
+     * }</code></pre>
+     *
+     * ...and at provide-time errors:
+     *
+     * <pre><code>Guice.createInjector().getInstance(Runnable.class);</code></pre>
+     *
+     * Otherwise we need to know who's calling when resolving a just-in-time binding, which makes
+     * things unnecessarily complex.
+     */
     public Errors missingImplementation(Key<?> key) {
-        return addMessage("No implementation for %s was bound.", key);
+        return addMessage(ErrorId.MISSING_IMPLEMENTATION, "No implementation for %s was bound.", key);
     }
 
     /** Within guice's core, allow for better missing binding messages */
     <T> Errors missingImplementationWithHint(Key<T> key, Injector injector) {
-        StringBuilder sb = new StringBuilder();
+        MissingImplementationError<T> error =
-
+                new MissingImplementationError<T>(key, injector, getSources());
-        sb.append(Messages.format("No implementation for %s was bound.", key));
+        return addMessage(
-
+                new Message(GuiceInternal.GUICE_INTERNAL, ErrorId.MISSING_IMPLEMENTATION, error));
-        // Keys which have similar strings as the desired key
-        List<String> possibleMatches = new ArrayList<>();
-
-        // Check for other keys that may have the same type,
-        // but not the same annotation
-        TypeLiteral<T> type = key.getTypeLiteral();
-        List<Binding<T>> sameTypes = injector.findBindingsByType(type);
-        if (!sameTypes.isEmpty()) {
-            sb.append(Messages.format("%n  Did you mean?"));
-            int howMany = Math.min(sameTypes.size(), MAX_MATCHING_TYPES_REPORTED);
-            for (int i = 0; i < howMany; ++i) {
-                // TODO: Look into a better way to prioritize suggestions. For example, possbily
-                // use levenshtein distance of the given annotation vs actual annotation.
-                sb.append(Messages.format("%n    * %s", sameTypes.get(i).getKey()));
-            }
-            int remaining = sameTypes.size() - MAX_MATCHING_TYPES_REPORTED;
-            if (remaining > 0) {
-                String plural = (remaining == 1) ? "" : "s";
-                sb.append(Messages.format("%n    %d more binding%s with other annotations.", remaining, plural));
-            }
-        } else {
-            // For now, do a simple substring search for possibilities. This can help spot
-            // issues when there are generics being used (such as a wrapper class) and the
-            // user has forgotten they need to bind based on the wrapper, not the underlying
-            // class. In the future, consider doing a strict in-depth type search.
-            // TODO: Look into a better way to prioritize suggestions. For example, possbily
-            // use levenshtein distance of the type literal strings.
-            String want = type.toString();
-            Map<Key<?>, Binding<?>> bindingMap = injector.getAllBindings();
-            for (Key<?> bindingKey : bindingMap.keySet()) {
-                String have = bindingKey.getTypeLiteral().toString();
-                if (have.contains(want) || want.contains(have)) {
-                    Formatter fmt = new Formatter();
-                    Messages.formatSource(fmt, bindingMap.get(bindingKey).getSource());
-                    String match = String.format("%s bound%s", Messages.convert(bindingKey), fmt.toString());
-                    possibleMatches.add(match);
-                    // TODO: Consider a check that if there are more than some number of results,
-                    // don't suggest any.
-                    if (possibleMatches.size() > MAX_RELATED_TYPES_REPORTED) {
-                        // Early exit if we have found more than we need.
-                        break;
-                    }
-                }
-            }
-
-            if ((possibleMatches.size() > 0) && (possibleMatches.size() <= MAX_RELATED_TYPES_REPORTED)) {
-                sb.append(Messages.format("%n  Did you mean?"));
-                for (String possibleMatch : possibleMatches) {
-                    sb.append(Messages.format("%n    %s", possibleMatch));
-                }
-            }
-        }
-
-        // If where are no possibilities to suggest, then handle the case of missing
-        // annotations on simple types. This is usually a bad idea.
-        if (sameTypes.isEmpty()
-                && possibleMatches.isEmpty()
-                && key.getAnnotationType() == null
-                && COMMON_AMBIGUOUS_TYPES.contains(key.getTypeLiteral().getRawType())) {
-            // We don't recommend using such simple types without annotations.
-            sb.append(Messages.format("%nThe key seems very generic, did you forget an annotation?"));
-        }
-
-        return addMessage(sb.toString());
     }
 
     public Errors jitDisabled(Key<?> key) {
-        return addMessage("Explicit bindings are required and %s is not explicitly bound.", key);
+        return addMessage(
+                ErrorId.JIT_DISABLED,
+                "Explicit bindings are required and %s is not explicitly bound.",
+                key);
     }
 
     public Errors jitDisabledInParent(Key<?> key) {
-        return addMessage("Explicit bindings are required and %s would be bound in a parent injector.%n"
+        return addMessage(
+                ErrorId.JIT_DISABLED_IN_PARENT,
+                "Explicit bindings are required and %s would be bound in a parent injector.%n"
                         + "Please add an explicit binding for it, either in the child or the parent.",
                 key);
     }
 
-    public Errors atInjectRequired(Class<?> clazz) {
+    public Errors atInjectRequired(TypeLiteral<?> type) {
-        return addMessage("Explicit @Inject annotations are required on constructors,"
+        return addMessage(
-                        + " but %s has no constructors annotated with @Inject.",
+                new Message(
-                clazz);
+                        GuiceInternal.GUICE_INTERNAL,
+                        ErrorId.MISSING_CONSTRUCTOR,
+                        new MissingConstructorError(type, /* atInjectRequired= */ true, getSources())));
     }
 
-    public Errors converterReturnedNull(String stringValue, Object source,
+    public Errors converterReturnedNull(
-                                        TypeLiteral<?> type, TypeConverterBinding typeConverterBinding) {
+            String stringValue,
-        return addMessage("Received null converting '%s' (bound at %s) to %s%n"
+            Object source,
-                        + " using %s.",
+            TypeLiteral<?> type,
-                stringValue, Messages.convert(source), type, typeConverterBinding);
+            TypeConverterBinding typeConverterBinding) {
+        return addMessage(
+                ErrorId.CONVERTER_RETURNED_NULL,
+                "Received null converting '%s' (bound at %s) to %s%n using %s.",
+                stringValue,
+                convert(source),
+                type,
+                typeConverterBinding);
     }
 
-    public Errors conversionTypeError(String stringValue, Object source, TypeLiteral<?> type,
+    public Errors conversionTypeError(
-                                      TypeConverterBinding typeConverterBinding, Object converted) {
+            String stringValue,
-        return addMessage("Type mismatch converting '%s' (bound at %s) to %s%n"
+            Object source,
+            TypeLiteral<?> type,
+            TypeConverterBinding typeConverterBinding,
+            Object converted) {
+        return addMessage(
+                ErrorId.CONVERSION_TYPE_ERROR,
+                "Type mismatch converting '%s' (bound at %s) to %s%n"
                         + " using %s.%n"
                         + " Converter returned %s.",
-                stringValue, Messages.convert(source), type, typeConverterBinding, converted);
+                stringValue,
+                convert(source),
+                type,
+                typeConverterBinding,
+                converted);
     }
 
-    public Errors conversionError(String stringValue, Object source,
+    public Errors conversionError(
-                                  TypeLiteral<?> type, TypeConverterBinding typeConverterBinding, RuntimeException cause) {
+            String stringValue,
-        return errorInUserCode(cause, "Error converting '%s' (bound at %s) to %s%n"
+            Object source,
-                        + " using %s.%n"
+            TypeLiteral<?> type,
-                        + " Reason: %s",
+            TypeConverterBinding typeConverterBinding,
-                stringValue, Messages.convert(source), type, typeConverterBinding, cause);
+            RuntimeException cause) {
+        return errorInUserCode(
+                cause,
+                "Error converting '%s' (bound at %s) to %s%n using %s.%n Reason: %s",
+                stringValue,
+                convert(source),
+                type,
+                typeConverterBinding,
+                cause);
     }
 
-    public Errors ambiguousTypeConversion(String stringValue, Object source, TypeLiteral<?> type,
+    public Errors ambiguousTypeConversion(
-                                          TypeConverterBinding a, TypeConverterBinding b) {
+            String stringValue,
-        return addMessage("Multiple converters can convert '%s' (bound at %s) to %s:%n"
+            Object source,
+            TypeLiteral<?> type,
+            TypeConverterBinding a,
+            TypeConverterBinding b) {
+        return addMessage(
+                ErrorId.AMBIGUOUS_TYPE_CONVERSION,
+                "Multiple converters can convert '%s' (bound at %s) to %s:%n"
                         + " %s and%n"
                         + " %s.%n"
                         + " Please adjust your type converter configuration to avoid overlapping matches.",
-                stringValue, Messages.convert(source), type, a, b);
+                stringValue,
+                convert(source),
+                type,
+                a,
+                b);
     }
 
     public Errors bindingToProvider() {
-        return addMessage("Binding to Provider is not allowed.");
+        return addMessage(ErrorId.BINDING_TO_PROVIDER, "Binding to Provider is not allowed.");
     }
 
     public Errors notASubtype(Class<?> implementationType, Class<?> type) {
-        return addMessage("%s doesn't extend %s.", implementationType, type);
+        return addMessage(ErrorId.NOT_A_SUBTYPE, "%s doesn't extend %s.", implementationType, type);
     }
 
     public Errors recursiveImplementationType() {
-        return addMessage("@ImplementedBy points to the same class it annotates.");
+        return addMessage(
+                ErrorId.RECURSIVE_IMPLEMENTATION_TYPE,
+                "@ImplementedBy points to the same class it annotates.");
     }
 
     public Errors recursiveProviderType() {
-        return addMessage("@ProvidedBy points to the same class it annotates.");
+        return addMessage(
+                ErrorId.RECURSIVE_PROVIDER_TYPE, "@ProvidedBy points to the same class it annotates.");
     }
 
     public Errors missingRuntimeRetention(Class<? extends Annotation> annotation) {
-        return addMessage(Messages.format("Please annotate %s with @Retention(RUNTIME).", annotation));
+        return addMessage(
+                ErrorId.MISSING_RUNTIME_RETENTION,
+                format("Please annotate %s with @Retention(RUNTIME).", annotation));
     }
 
     public Errors missingScopeAnnotation(Class<? extends Annotation> annotation) {
-        return addMessage(Messages.format("Please annotate %s with @ScopeAnnotation.", annotation));
+        return addMessage(
+                ErrorId.MISSING_SCOPE_ANNOTATION,
+                format("Please annotate %s with @ScopeAnnotation.", annotation));
     }
 
     public Errors optionalConstructor(Constructor<?> constructor) {
-        return addMessage("%s is annotated @Inject(optional=true), "
+        return addMessage(
-                + "but constructors cannot be optional.", constructor);
+                ErrorId.OPTIONAL_CONSTRUCTOR,
+                "%s is annotated @Inject(optional=true), but constructors cannot be optional.",
+                constructor);
     }
 
     public Errors cannotBindToGuiceType(String simpleName) {
-        return addMessage("Binding to core guice framework type is not allowed: %s.", simpleName);
+        return addMessage(
+                ErrorId.BINDING_TO_GUICE_TYPE,
+                "Binding to core guice framework type is not allowed: %s.",
+                simpleName);
     }
 
     public Errors scopeNotFound(Class<? extends Annotation> scopeAnnotation) {
-        return addMessage("No scope is bound to %s.", scopeAnnotation);
+        return addMessage(
+                new Message(
+                        GuiceInternal.GUICE_INTERNAL,
+                        ErrorId.SCOPE_NOT_FOUND,
+                        new ScopeNotFoundError(scopeAnnotation, getSources())));
     }
 
     public Errors scopeAnnotationOnAbstractType(
             Class<? extends Annotation> scopeAnnotation, Class<?> type, Object source) {
-        return addMessage("%s is annotated with %s, but scope annotations are not supported "
+        return addMessage(
-                + "for abstract types.%n Bound at %s.", type, scopeAnnotation, Messages.convert(source));
+                ErrorId.SCOPE_ANNOTATION_ON_ABSTRACT_TYPE,
+                "%s is annotated with %s, but scope annotations are not supported "
+                        + "for abstract types.%n Bound at %s.",
+                type,
+                scopeAnnotation,
+                convert(source));
     }
 
     public Errors misplacedBindingAnnotation(Member member, Annotation bindingAnnotation) {
-        return addMessage("%s is annotated with %s, but binding annotations should be applied "
+        return addMessage(
-                + "to its parameters instead.", member, bindingAnnotation);
+                ErrorId.MISPLACED_BINDING_ANNOTATION,
+                "%s is annotated with %s, but binding annotations should be applied "
+                        + "to its parameters instead.",
+                member,
+                bindingAnnotation);
     }
 
+    // TODO(diamondm) don't mention zero-arg constructors if requireAtInjectOnConstructors is true
     private static final String CONSTRUCTOR_RULES =
             "Injectable classes must have either one (and only one) constructor annotated with @Inject"
                     + " or a zero-argument constructor that is not private.";
 
     public Errors missingConstructor(TypeLiteral<?> type) {
-        // Don't bother including the type in the message twice, unless the type is generic (i.e. the
-        // type has generics that the raw class loses)
-        String typeString = type.toString();
-        String rawTypeString = MoreTypes.getRawType(type.getType()).getName();
         return addMessage(
-                "No implementation for %s (with no qualifier annotation) was bound, and could not find an"
+                new Message(
-                        + " injectable constructor%s. %s",
+                        GuiceInternal.GUICE_INTERNAL,
-                typeString,
+                        ErrorId.MISSING_CONSTRUCTOR,
-                typeString.equals(rawTypeString) ? "" : " in " + rawTypeString,
+                        new MissingConstructorError(type, /* atInjectRequired= */ false, getSources())));
-                CONSTRUCTOR_RULES);
     }
 
     public Errors tooManyConstructors(Class<?> implementation) {
         return addMessage(
+                ErrorId.TOO_MANY_CONSTRUCTORS,
                 "%s has more than one constructor annotated with @Inject. %s",
-                implementation, CONSTRUCTOR_RULES);
+                implementation,
+                CONSTRUCTOR_RULES);
     }
 
     public Errors constructorNotDefinedByType(Constructor<?> constructor, TypeLiteral<?> type) {
-        return addMessage("%s does not define %s", type, constructor);
+        return addMessage(
+                ErrorId.CONSTRUCTOR_NOT_DEFINED_BY_TYPE, "%s does not define %s", type, constructor);
     }
 
-    public Errors duplicateScopes(ScopeBinding existing,
+    public <K, V> Errors duplicateMapKey(Key<Map<K, V>> mapKey, Multimap<K, Binding<V>> duplicates) {
-                                  Class<? extends Annotation> annotationType, Scope scope) {
+        return addMessage(
-        return addMessage("Scope %s is already bound to %s at %s.%n Cannot bind %s.",
+                new Message(
-                existing.getScope(), annotationType, existing.getSource(), scope);
+                        GuiceInternal.GUICE_INTERNAL,
+                        ErrorId.DUPLICATE_MAP_KEY,
+                        new DuplicateMapKeyError<K, V>(mapKey, duplicates, getSources())));
+    }
+
+    public Errors duplicateScopes(
+            ScopeBinding existing, Class<? extends Annotation> annotationType, Scope scope) {
+        return addMessage(
+                ErrorId.DUPLICATE_SCOPES,
+                "Scope %s is already bound to %s at %s.%n Cannot bind %s.",
+                existing.getScope(),
+                annotationType,
+                existing.getSource(),
+                scope);
     }
 
     public Errors voidProviderMethod() {
-        return addMessage("Provider methods must return a value. Do not return void.");
+        return addMessage(
+                ErrorId.VOID_PROVIDER_METHOD, "Provider methods must return a value. Do not return void.");
     }
 
     public Errors missingConstantValues() {
-        return addMessage("Missing constant value. Please call to(...).");
+        return addMessage(
+                ErrorId.MISSING_CONSTANT_VALUES, "Missing constant value. Please call to(...).");
     }
 
     public Errors cannotInjectInnerClass(Class<?> type) {
-        return addMessage("Injecting into inner classes is not supported.  "
+        return addMessage(
-                + "Please use a 'static' class (top-level or nested) instead of %s.", type);
+                ErrorId.INJECT_INNER_CLASS,
+                "Injecting into inner classes is not supported.  "
+                        + "Please use a 'static' class (top-level or nested) instead of %s.",
+                type);
     }
 
-    public Errors duplicateBindingAnnotations(Member member,
+    public Errors duplicateBindingAnnotations(
-                                              Class<? extends Annotation> a, Class<? extends Annotation> b) {
+            Member member, Class<? extends Annotation> a, Class<? extends Annotation> b) {
-        return addMessage("%s has more than one annotation annotated with @BindingAnnotation: "
+        return addMessage(
-                + "%s and %s", member, a, b);
+                ErrorId.DUPLICATE_BINDING_ANNOTATIONS,
+                "%s has more than one annotation annotated with @BindingAnnotation: %s and %s",
+                member,
+                a,
+                b);
     }
 
     public Errors staticInjectionOnInterface(Class<?> clazz) {
-        return addMessage("%s is an interface, but interfaces have no static injection points.", clazz);
+        return addMessage(
+                ErrorId.STATIC_INJECTION_ON_INTERFACE,
+                "%s is an interface, but interfaces have no static injection points.",
+                clazz);
     }
 
     public Errors cannotInjectFinalField(Field field) {
-        return addMessage("Injected field %s cannot be final.", field);
+        return addMessage(ErrorId.INJECT_FINAL_FIELD, "Injected field %s cannot be final.", field);
+    }
+
+    public Errors atTargetIsMissingParameter(
+            Annotation bindingAnnotation, String parameterName, Class<?> clazz) {
+        return addMessage(
+                ErrorId.AT_TARGET_IS_MISSING_PARAMETER,
+                "Binding annotation %s must have PARAMETER listed in its @Targets. It was used on"
+                        + " constructor parameter %s in %s.",
+                bindingAnnotation,
+                parameterName,
+                clazz);
     }
 
     public Errors cannotInjectAbstractMethod(Method method) {
-        return addMessage("Injected method %s cannot be abstract.", method);
+        return addMessage(
-    }
+                ErrorId.INJECT_ABSTRACT_METHOD, "Injected method %s cannot be abstract.", method);
-
-    public Errors cannotInjectNonVoidMethod(Method method) {
-        return addMessage("Injected method %s must return void.", method);
     }
 
     public Errors cannotInjectMethodWithTypeParameters(Method method) {
-        return addMessage("Injected method %s cannot declare type parameters of its own.", method);
+        return addMessage(
+                ErrorId.INJECT_METHOD_WITH_TYPE_PARAMETER,
+                "Injected method %s cannot declare type parameters of its own.",
+                method);
     }
 
     public Errors duplicateScopeAnnotations(
             Class<? extends Annotation> a, Class<? extends Annotation> b) {
-        return addMessage("More than one scope annotation was found: %s and %s.", a, b);
+        return addMessage(
+                ErrorId.DUPLICATE_SCOPE_ANNOTATIONS,
+                "More than one scope annotation was found: %s and %s.",
+                a,
+                b);
     }
 
-    public Errors recursiveBinding() {
+    public Errors recursiveBinding(Key<?> key, Key<?> linkedKey) {
-        return addMessage("Binding points to itself.");
+        return addMessage(
+                ErrorId.RECURSIVE_BINDING, "Binding points to itself. Key: %s", Messages.convert(key));
+    }
+
+    Errors bindingAlreadySet(Binding<?> binding, Binding<?> original) {
+        BindingAlreadySetError error = new BindingAlreadySetError(binding, original, getSources());
+        return addMessage(
+                new Message(GuiceInternal.GUICE_INTERNAL, ErrorId.BINDING_ALREADY_SET, error));
     }
 
     public Errors bindingAlreadySet(Key<?> key, Object source) {
-        return addMessage("A binding to %s was already configured at %s.", key, Messages.convert(source));
+        return addMessage(
+                ErrorId.BINDING_ALREADY_SET,
+                "A binding to %s was already configured at %s.",
+                key,
+                convert(source));
     }
 
     public Errors jitBindingAlreadySet(Key<?> key) {
-        return addMessage("A just-in-time binding to %s was already configured on a parent injector.", key);
+        return addMessage(
+                ErrorId.JIT_BINDING_ALREADY_SET,
+                "A just-in-time binding to %s was already configured on a parent injector.",
+                key);
     }
 
     public Errors childBindingAlreadySet(Key<?> key, Set<Object> sources) {
-        Formatter allSources = new Formatter();
+        Message message =
-        for (Object source : sources) {
+                new Message(
-            if (source == null) {
+                        GuiceInternal.GUICE_INTERNAL,
-                allSources.format("%n    (bound by a just-in-time binding)");
+                        ErrorId.CHILD_BINDING_ALREADY_SET,
-            } else {
+                        new ChildBindingAlreadySetError(key, sources, getSources()));
-                allSources.format("%n    bound at %s", source);
+        return addMessage(message);
-            }
-        }
-        return addMessage(
-                "Unable to create binding for %s."
-                        + " It was already configured on one or more child injectors or private modules"
-                        + "%s%n"
-                        + "  If it was in a PrivateModule, did you forget to expose the binding?",
-                key, allSources.out());
     }
 
     public Errors errorCheckingDuplicateBinding(Key<?> key, Object source, Throwable t) {
         return addMessage(
+                ErrorId.OTHER,
                 "A binding to %s was already configured at %s and an error was thrown "
                         + "while checking duplicate bindings.  Error: %s",
-                key, Messages.convert(source), t);
+                key,
+                convert(source),
+                t);
     }
 
-    public Errors errorNotifyingTypeListener(TypeListenerBinding listener,
+    public Errors errorNotifyingTypeListener(
-                                             TypeLiteral<?> type, Throwable cause) {
+            TypeListenerBinding listener, TypeLiteral<?> type, Throwable cause) {
-        return errorInUserCode(cause,
+        return errorInUserCode(
-                "Error notifying TypeListener %s (bound at %s) of %s.%n"
+                cause,
-                        + " Reason: %s",
+                "Error notifying TypeListener %s (bound at %s) of %s.%n Reason: %s",
-                listener.getListener(), Messages.convert(listener.getSource()), type, cause);
+                listener.getListener(),
+                convert(listener.getSource()),
+                type,
+                cause);
     }
 
     public Errors exposedButNotBound(Key<?> key) {
-        return addMessage("Could not expose() %s, it must be explicitly bound.", key);
+        return addMessage(
+                ErrorId.EXPOSED_BUT_NOT_BOUND, "Could not expose() %s, it must be explicitly bound.", key);
     }
 
     public Errors keyNotFullySpecified(TypeLiteral<?> typeLiteral) {
-        return addMessage("%s cannot be used as a key; It is not fully specified.", typeLiteral);
+        return addMessage(
+                ErrorId.KEY_NOT_FULLY_SPECIFIED,
+                "%s cannot be used as a key; It is not fully specified.",
+                typeLiteral);
     }
 
     public Errors errorEnhancingClass(Class<?> clazz, Throwable cause) {
@@ -439,39 +511,55 @@ public final class Errors {
         if (!messages.isEmpty()) {
             return merge(messages);
         } else {
-            return addMessage(cause, messageFormat, arguments);
+            return addMessage(ErrorId.ERROR_IN_USER_CODE, cause, messageFormat, arguments);
         }
     }
 
-
     public Errors cannotInjectRawProvider() {
-        return addMessage("Cannot inject a Provider that has no type parameter");
+        return addMessage(
+                ErrorId.INJECT_RAW_PROVIDER, "Cannot inject a Provider that has no type parameter");
     }
 
     public Errors cannotInjectRawMembersInjector() {
-        return addMessage("Cannot inject a MembersInjector that has no type parameter");
+        return addMessage(
+                ErrorId.INJECT_RAW_MEMBERS_INJECTOR,
+                "Cannot inject a MembersInjector that has no type parameter");
     }
 
     public Errors cannotInjectTypeLiteralOf(Type unsupportedType) {
-        return addMessage("Cannot inject a TypeLiteral of %s", unsupportedType);
+        return addMessage(ErrorId.OTHER, "Cannot inject a TypeLiteral of %s", unsupportedType);
     }
 
     public Errors cannotInjectRawTypeLiteral() {
-        return addMessage("Cannot inject a TypeLiteral that has no type parameter");
+        return addMessage(
+                ErrorId.INJECT_RAW_TYPE_LITERAL, "Cannot inject a TypeLiteral that has no type parameter");
     }
 
     public void throwCreationExceptionIfErrorsExist() {
         if (!hasErrors()) {
             return;
         }
-        throw new CreationException(getMessages());
+
+        CreationException exception = new CreationException(getMessages());
+        throw exception;
     }
 
     public void throwConfigurationExceptionIfErrorsExist() {
         if (!hasErrors()) {
             return;
         }
-        throw new ConfigurationException(getMessages());
+
+        ConfigurationException exception = new ConfigurationException(getMessages());
+        throw exception;
+    }
+
+    // Guice no longer calls this, but external callers do
+    public void throwProvisionExceptionIfErrorsExist() {
+        if (!hasErrors()) {
+            return;
+        }
+        ProvisionException exception = new ProvisionException(getMessages());
+        throw exception;
     }
 
     public Errors merge(Collection<Message> messages) {
@@ -486,6 +574,7 @@ public final class Errors {
         if (moreErrors.root == root || moreErrors.root.errors == null) {
             return this;
         }
+
         merge(moreErrors.root.errors);
         return this;
     }
@@ -495,7 +584,7 @@ public final class Errors {
         return this;
     }
 
-    public List<Object> getSources() {
+    private List<Object> getSources() {
         List<Object> sources = Lists.newArrayList();
         for (Errors e = this; e != null; e = e.parent) {
             if (e.source != SourceProvider.UNKNOWN_SOURCE) {
@@ -522,11 +611,16 @@ public final class Errors {
     }
 
     public Errors addMessage(String messageFormat, Object... arguments) {
-        return addMessage(null, messageFormat, arguments);
+        return addMessage(ErrorId.OTHER, null, messageFormat, arguments);
     }
 
-    private Errors addMessage(Throwable cause, String messageFormat, Object... arguments) {
+    public Errors addMessage(ErrorId errorId, String messageFormat, Object... arguments) {
-        addMessage(Messages.create(cause, getSources(), messageFormat, arguments));
+        return addMessage(errorId, null, messageFormat, arguments);
+    }
+
+    private Errors addMessage(
+            ErrorId errorId, Throwable cause, String messageFormat, Object... arguments) {
+        addMessage(Messages.create(errorId, cause, getSources(), messageFormat, arguments));
         return this;
     }
 
@@ -538,10 +632,16 @@ public final class Errors {
         return this;
     }
 
+    // TODO(lukes): inline into callers
+    public static String format(String messageFormat, Object... arguments) {
+        return Messages.format(messageFormat, arguments);
+    }
+
     public List<Message> getMessages() {
         if (root.errors == null) {
             return ImmutableList.of();
         }
+
         return new Ordering<Message>() {
             @Override
             public int compare(Message a, Message b) {
@@ -553,4 +653,20 @@ public final class Errors {
     public int size() {
         return root.errors == null ? 0 : root.errors.size();
     }
+
+    // TODO(lukes): inline in callers.  There are some callers outside of guice, so this is difficult
+    public static Object convert(Object o) {
+        return Messages.convert(o);
+    }
+
+    // TODO(lukes): inline in callers.  There are some callers outside of guice, so this is difficult
+    public static Object convert(Object o, ElementSource source) {
+        return Messages.convert(o, source);
+    }
+
+    // TODO(lukes): inline in callers.  There are some callers outside of guice, so this is difficult
+    public static void formatSource(Formatter formatter, Object source) {
+        formatter.format("  ");
+        new SourceFormatter(source, formatter, false).format();
+    }
 }

src/main/java/com/google/inject/internal/ExposedKeyFactory.java

@@ -21,7 +21,7 @@ final class ExposedKeyFactory<T> implements InternalFactory<T>, CreationListener
     @Override
     public void notify(Errors errors) {
         InjectorImpl privateInjector = (InjectorImpl) privateElements.getInjector();
-        BindingImpl<T> explicitBinding = privateInjector.state.getExplicitBinding(key);
+        BindingImpl<T> explicitBinding = privateInjector.getBindingData().getExplicitBinding(key);
 
         // validate that the child injector has its own factory. If the getInternalFactory() returns
         // this, then that child injector doesn't have a factory (and getExplicitBinding has returned
@@ -34,8 +34,10 @@ final class ExposedKeyFactory<T> implements InternalFactory<T>, CreationListener
         this.delegate = explicitBinding;
     }
 
+    @Override
     public T get(InternalContext context, Dependency<?> dependency, boolean linked)
             throws InternalProvisionException {
+        // TODO(lukes): add a source to the thrown exception?
         return delegate.getInternalFactory().get(context, dependency, linked);
     }
 }

src/main/java/com/google/inject/internal/GenericErrorDetail.java

@@ -0,0 +1,34 @@
+package com.google.inject.internal;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Lists;
+import com.google.inject.spi.ErrorDetail;
+import java.io.Serializable;
+import java.util.Formatter;
+import java.util.List;
+
+/** Generic error message representing a Guice internal error. */
+public final class GenericErrorDetail extends InternalErrorDetail<GenericErrorDetail>
+        implements Serializable {
+    public GenericErrorDetail(
+            ErrorId errorId, String message, List<Object> sources, Throwable cause) {
+        super(errorId, checkNotNull(message, "message"), sources, cause);
+    }
+
+    @Override
+    public void formatDetail(List<ErrorDetail<?>> mergeableErrors, Formatter formatter) {
+        Preconditions.checkArgument(mergeableErrors.isEmpty(), "Unexpected mergeable errors");
+        List<Object> dependencies = getSources();
+        for (Object source : Lists.reverse(dependencies)) {
+            formatter.format("  ");
+            new SourceFormatter(source, formatter, /* omitPreposition= */ false).format();
+        }
+    }
+
+    @Override
+    public GenericErrorDetail withSources(List<Object> newSources) {
+        return new GenericErrorDetail(errorId, getMessage(), newSources, getCause());
+    }
+}

src/main/java/com/google/inject/internal/GuiceInternal.java

@@ -0,0 +1,14 @@
+package com.google.inject.internal;
+
+/**
+ * Class used for restricting APIs in other packages to only be used by this package.
+ *
+ * <p>Other packages can reference this class but only this package can reference an instance of it,
+ * so adding this class as a method param ensures that only this package can call it (provided null
+ * is disallowed).
+ */
+public final class GuiceInternal {
+  static final GuiceInternal GUICE_INTERNAL = new GuiceInternal();
+
+  private GuiceInternal() {}
+}

src/main/java/com/google/inject/internal/InjectorBindingData.java

@@ -1,6 +1,9 @@
 package com.google.inject.internal;
 
+import com.google.common.collect.ArrayListMultimap;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ListMultimap;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
@@ -17,19 +20,22 @@ import com.google.inject.spi.ScopeBinding;
 import com.google.inject.spi.StaticInjectionRequest;
 import com.google.inject.spi.TypeConverterBinding;
 import com.google.inject.spi.TypeListenerBinding;
-
 import java.lang.annotation.Annotation;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Set;
 
-import static com.google.common.base.Preconditions.checkNotNull;
+/**
+ * A container that stores an injector's binding data. This excludes JIT binding data, which is
+ * stored in {@link InjectorJitBindingData}.
+ */
+class InjectorBindingData {
 
-final class InheritingState implements State {
+    // The parent injector's InjectorBindingData, if the parent injector exists.
-
+    private final Optional<InjectorBindingData> parent;
-    private final State parent;
 
     // Must be a linked hashmap in order to preserve order of bindings in Modules.
     private final Map<Key<?>, Binding<?>> explicitBindingsMutable = Maps.newLinkedHashMap();
@@ -44,109 +50,97 @@ final class InheritingState implements State {
     private final List<TypeListenerBinding> typeListenerBindings = Lists.newArrayList();
     private final List<ProvisionListenerBinding> provisionListenerBindings = Lists.newArrayList();
     private final List<ModuleAnnotatedMethodScannerBinding> scannerBindings = Lists.newArrayList();
-    private final WeakKeySet blacklistedKeys;
+    // The injector's explicit bindings, indexed by the binding's type.
-    private final Object lock;
+    private final ListMultimap<TypeLiteral<?>, Binding<?>> indexedExplicitBindings =
+            ArrayListMultimap.create();
 
-    InheritingState(State parent) {
+    InjectorBindingData(Optional<InjectorBindingData> parent) {
-        this.parent = checkNotNull(parent, "parent");
+        this.parent = parent;
-        this.lock = (parent == State.NONE) ? this : parent.lock();
-        this.blacklistedKeys = new WeakKeySet(lock);
     }
 
-    @Override
+    public Optional<InjectorBindingData> parent() {
-    public State parent() {
         return parent;
     }
 
     @SuppressWarnings("unchecked") // we only put in BindingImpls that match their key types
-    @Override
     public <T> BindingImpl<T> getExplicitBinding(Key<T> key) {
         Binding<?> binding = explicitBindings.get(key);
-        return binding != null ? (BindingImpl<T>) binding : parent.getExplicitBinding(key);
+        if (binding == null && parent.isPresent()) {
+            return parent.get().getExplicitBinding(key);
+        }
+        return (BindingImpl<T>) binding;
     }
 
-    @Override
     public Map<Key<?>, Binding<?>> getExplicitBindingsThisLevel() {
         return explicitBindings;
     }
 
-    @Override
     public void putBinding(Key<?> key, BindingImpl<?> binding) {
         explicitBindingsMutable.put(key, binding);
     }
 
-    @Override
     public void putProviderLookup(ProviderLookup<?> lookup) {
         providerLookups.add(lookup);
     }
 
-    @Override
     public Set<ProviderLookup<?>> getProviderLookupsThisLevel() {
         return providerLookups;
     }
 
-    @Override
     public void putStaticInjectionRequest(StaticInjectionRequest staticInjectionRequest) {
         staticInjectionRequests.add(staticInjectionRequest);
     }
 
-    @Override
     public Set<StaticInjectionRequest> getStaticInjectionRequestsThisLevel() {
         return staticInjectionRequests;
     }
 
-    @Override
     public void putInjectionRequest(InjectionRequest<?> injectionRequest) {
         injectionRequests.add(injectionRequest);
     }
 
-    @Override
     public Set<InjectionRequest<?>> getInjectionRequestsThisLevel() {
         return injectionRequests;
     }
 
-    @Override
     public void putMembersInjectorLookup(MembersInjectorLookup<?> membersInjectorLookup) {
         membersInjectorLookups.add(membersInjectorLookup);
     }
 
-    @Override
     public Set<MembersInjectorLookup<?>> getMembersInjectorLookupsThisLevel() {
         return membersInjectorLookups;
     }
 
-    @Override
     public ScopeBinding getScopeBinding(Class<? extends Annotation> annotationType) {
         ScopeBinding scopeBinding = scopes.get(annotationType);
-        return scopeBinding != null ? scopeBinding : parent.getScopeBinding(annotationType);
+        if (scopeBinding == null && parent.isPresent()) {
+            return parent.get().getScopeBinding(annotationType);
+        }
+        return scopeBinding;
     }
 
-    @Override
     public void putScopeBinding(Class<? extends Annotation> annotationType, ScopeBinding scope) {
         scopes.put(annotationType, scope);
     }
 
-    @Override
     public Collection<ScopeBinding> getScopeBindingsThisLevel() {
         return scopes.values();
     }
 
-    @Override
     public Iterable<TypeConverterBinding> getConvertersThisLevel() {
         return converters;
     }
 
-    @Override
     public void addConverter(TypeConverterBinding typeConverterBinding) {
         converters.add(typeConverterBinding);
     }
 
-    @Override
     public TypeConverterBinding getConverter(
             String stringValue, TypeLiteral<?> type, Errors errors, Object source) {
         TypeConverterBinding matchingConverter = null;
-        for (State s = this; s != State.NONE; s = s.parent()) {
+        InjectorBindingData b = this;
-            for (TypeConverterBinding converter : s.getConvertersThisLevel()) {
+        while (b != null) {
+            for (TypeConverterBinding converter : b.getConvertersThisLevel()) {
                 if (converter.getTypeMatcher().matches(type)) {
                     if (matchingConverter != null) {
                         errors.ambiguousTypeConversion(stringValue, source, type, matchingConverter, converter);
@@ -154,92 +148,65 @@ final class InheritingState implements State {
                     matchingConverter = converter;
                 }
             }
+            b = b.parent().orElse(null);
         }
         return matchingConverter;
     }
 
-    @Override
     public void addTypeListener(TypeListenerBinding listenerBinding) {
         typeListenerBindings.add(listenerBinding);
     }
 
-    @Override
+    public ImmutableList<TypeListenerBinding> getTypeListenerBindings() {
-    public List<TypeListenerBinding> getTypeListenerBindings() {
+        if (parent.isPresent()) {
-        List<TypeListenerBinding> parentBindings = parent.getTypeListenerBindings();
+            return new ImmutableList.Builder<TypeListenerBinding>()
-        List<TypeListenerBinding> result =
+                    .addAll(parent.get().getTypeListenerBindings())
-                Lists.newArrayListWithCapacity(parentBindings.size() + typeListenerBindings.size());
+                    .addAll(typeListenerBindings)
-        result.addAll(parentBindings);
+                    .build();
-        result.addAll(typeListenerBindings);
+        }
-        return result;
+        return ImmutableList.copyOf(typeListenerBindings);
     }
 
-    @Override
+    public ImmutableList<TypeListenerBinding> getTypeListenerBindingsThisLevel() {
-    public List<TypeListenerBinding> getTypeListenerBindingsThisLevel() {
+        return ImmutableList.copyOf(typeListenerBindings);
-        return typeListenerBindings;
     }
 
-    @Override
     public void addProvisionListener(ProvisionListenerBinding listenerBinding) {
         provisionListenerBindings.add(listenerBinding);
     }
 
-    @Override
+    public ImmutableList<ProvisionListenerBinding> getProvisionListenerBindings() {
-    public List<ProvisionListenerBinding> getProvisionListenerBindings() {
+        if (parent.isPresent()) {
-        List<ProvisionListenerBinding> parentBindings = parent.getProvisionListenerBindings();
+            return new ImmutableList.Builder<ProvisionListenerBinding>()
-        List<ProvisionListenerBinding> result =
+                    .addAll(parent.get().getProvisionListenerBindings())
-                Lists.newArrayListWithCapacity(parentBindings.size() + provisionListenerBindings.size());
+                    .addAll(provisionListenerBindings)
-        result.addAll(parentBindings);
+                    .build();
-        result.addAll(provisionListenerBindings);
+        }
-        return result;
+        return ImmutableList.copyOf(provisionListenerBindings);
     }
 
-    @Override
+    public ImmutableList<ProvisionListenerBinding> getProvisionListenerBindingsThisLevel() {
-    public List<ProvisionListenerBinding> getProvisionListenerBindingsThisLevel() {
+        return ImmutableList.copyOf(provisionListenerBindings);
-        return provisionListenerBindings;
     }
 
-    @Override
     public void addScanner(ModuleAnnotatedMethodScannerBinding scanner) {
         scannerBindings.add(scanner);
     }
 
-    @Override
+    public ImmutableList<ModuleAnnotatedMethodScannerBinding> getScannerBindings() {
-    public List<ModuleAnnotatedMethodScannerBinding> getScannerBindings() {
+        if (parent.isPresent()) {
-        List<ModuleAnnotatedMethodScannerBinding> parentBindings = parent.getScannerBindings();
+            return new ImmutableList.Builder<ModuleAnnotatedMethodScannerBinding>()
-        List<ModuleAnnotatedMethodScannerBinding> result =
+                    .addAll(parent.get().getScannerBindings())
-                Lists.newArrayListWithCapacity(parentBindings.size() + scannerBindings.size());
+                    .addAll(scannerBindings)
-        result.addAll(parentBindings);
+                    .build();
-        result.addAll(scannerBindings);
+        }
-        return result;
+        return ImmutableList.copyOf(scannerBindings);
     }
 
-    @Override
+    public ImmutableList<ModuleAnnotatedMethodScannerBinding> getScannerBindingsThisLevel() {
-    public List<ModuleAnnotatedMethodScannerBinding> getScannerBindingsThisLevel() {
+        return ImmutableList.copyOf(scannerBindings);
-        return scannerBindings;
     }
 
-    @Override
-    public void blacklist(Key<?> key, State state, Object source) {
-        parent.blacklist(key, state, source);
-        blacklistedKeys.add(key, state, source);
-    }
-
-    @Override
-    public boolean isBlacklisted(Key<?> key) {
-        return blacklistedKeys.contains(key);
-    }
-
-    @Override
-    public Set<Object> getSourcesForBlacklistedKey(Key<?> key) {
-        return blacklistedKeys.getSources(key);
-    }
-
-    @Override
-    public Object lock() {
-        return lock;
-    }
-
-    @Override
     public Map<Class<? extends Annotation>, Scope> getScopes() {
         ImmutableMap.Builder<Class<? extends Annotation>, Scope> builder = ImmutableMap.builder();
         for (Map.Entry<Class<? extends Annotation>, ScopeBinding> entry : scopes.entrySet()) {
@@ -247,4 +214,18 @@ final class InheritingState implements State {
         }
         return builder.build();
     }
+
+    /**
+     * Once the injector's explicit bindings are finalized, this method is called to index all
+     * explicit bindings by their return type.
+     */
+    void indexBindingsByType() {
+        for (Binding<?> binding : getExplicitBindingsThisLevel().values()) {
+            indexedExplicitBindings.put(binding.getKey().getTypeLiteral(), binding);
+        }
+    }
+
+    public ListMultimap<TypeLiteral<?>, Binding<?>> getIndexedExplicitBindings() {
+        return indexedExplicitBindings;
+    }
 }

src/main/java/com/google/inject/internal/InjectorJitBindingData.java

@@ -0,0 +1,106 @@
+package com.google.inject.internal;
+
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import com.google.inject.Key;
+import java.util.Collections;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+
+/**
+ * A container for most just-in-time (JIT) binding data corresponding to an Injector. It
+ * includes @Inject constructor bindings. It does not include {@link MembersInjectorStore} or {@link
+ * ProvisionListenerCallbackStore}, which are still stored in {@link InjectorImpl}.
+ */
+final class InjectorJitBindingData {
+    /** Just-in-time binding cache. Guarded by {@link #lock}. */
+    private final Map<Key<?>, BindingImpl<?>> jitBindings = Maps.newHashMap();
+    /**
+     * Cache of Keys that we were unable to create JIT bindings for, so we don't keep trying. Guarded
+     * by {@link #lock}.
+     */
+    private final Set<Key<?>> failedJitBindings = Sets.newHashSet();
+
+    // The set of JIT binding keys that are banned for this particular injector, because a binding
+    // already exists in a child injector. Guarded by {@link #lock}.
+    private final WeakKeySet bannedKeys;
+
+    // The InjectorJitBindingData corresponding to the Injector's parent, if it exists.
+    private final Optional<InjectorJitBindingData> parent;
+
+    /**
+     * This lock is needed for threadsafe InjectorJitBindingData accesses. It corresponds to this
+     * InjectorJitBindingData's highest ancestor.
+     */
+    private final Object lock;
+
+    InjectorJitBindingData(Optional<InjectorJitBindingData> parent) {
+        this.parent = parent;
+        this.lock = parent.isPresent() ? parent.get().lock() : this;
+        this.bannedKeys = new WeakKeySet(lock);
+    }
+
+    Map<Key<?>, BindingImpl<?>> getJitBindings() {
+        return Collections.unmodifiableMap(jitBindings);
+    }
+
+    BindingImpl<?> getJitBinding(Key<?> key) {
+        return jitBindings.get(key);
+    }
+
+    void putJitBinding(Key<?> key, BindingImpl<?> binding) {
+        jitBindings.put(key, binding);
+    }
+
+    void removeJitBinding(Key<?> key) {
+        jitBindings.remove(key);
+    }
+
+    boolean isFailedJitBinding(Key<?> key) {
+        return failedJitBindings.contains(key);
+    }
+
+    void addFailedJitBinding(Key<?> key) {
+        failedJitBindings.add(key);
+    }
+
+    /**
+     * Forbids the corresponding injector and its ancestors from creating a binding to {@code key}.
+     * Child injectors ban their bound keys on their parent injectors to prevent just-in-time bindings
+     * on the parent injector that would conflict, and pass along their InjectorBindingData to control
+     * the banned key's lifetime.
+     */
+    void banKey(Key<?> key, InjectorBindingData injectorBindingData, Object source) {
+        banKeyInParent(key, injectorBindingData, source);
+        bannedKeys.add(key, injectorBindingData, source);
+    }
+
+    /**
+     * Similar to {@link #banKey(Key, InjectorBindingData, Object)} but we only begin banning the
+     * binding at the parent level. This is used to prevent JIT bindings in the parent injector from
+     * overriding explicit bindings declared in a child injector.
+     */
+    void banKeyInParent(Key<?> key, InjectorBindingData injectorBindingData, Object source) {
+        if (parent.isPresent()) {
+            parent.get().banKey(key, injectorBindingData, source);
+        }
+    }
+
+    /**
+     * Returns true if {@code key} is forbidden from being bound in the injector corresponding to this
+     * data object. This indicates that one of the injector's children has bound the key.
+     */
+    boolean isBannedKey(Key<?> key) {
+        return bannedKeys.contains(key);
+    }
+
+    /** Returns the source of a banned key. */
+    Set<Object> getSourcesForBannedKey(Key<?> key) {
+        return bannedKeys.getSources(key);
+    }
+
+    Object lock() {
+        return lock;
+    }
+}

src/main/java/com/google/inject/internal/InjectorShell.java

@@ -1,5 +1,9 @@
 package com.google.inject.internal;
 
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.inject.Scopes.SINGLETON;
+import static com.google.inject.internal.GuiceInternal.GUICE_INTERNAL;
+
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
 import com.google.inject.Binder;
@@ -10,24 +14,34 @@ import com.google.inject.Provider;
 import com.google.inject.Singleton;
 import com.google.inject.Stage;
 import com.google.inject.internal.InjectorImpl.InjectorOptions;
+import com.google.inject.internal.util.ContinuousStopwatch;
 import com.google.inject.internal.util.SourceProvider;
-import com.google.inject.internal.util.Stopwatch;
+import com.google.inject.spi.BindingSourceRestriction;
 import com.google.inject.spi.Dependency;
 import com.google.inject.spi.Element;
 import com.google.inject.spi.Elements;
+import com.google.inject.spi.InjectionPoint;
 import com.google.inject.spi.ModuleAnnotatedMethodScannerBinding;
 import com.google.inject.spi.PrivateElements;
 import com.google.inject.spi.ProvisionListenerBinding;
 import com.google.inject.spi.TypeListenerBinding;
-
 import java.util.List;
-
+import java.util.Optional;
-import static com.google.common.base.Preconditions.checkState;
+import java.util.logging.Logger;
-import static com.google.inject.Scopes.SINGLETON;
 
 /**
- * A partially-initialized injector. See {@link InternalInjectorCreator}, which
+ * InjectorShell is used by {@link InternalInjectorCreator} to recursively create a tree of
- * uses this to build a tree of injectors in batch.
+ * uninitialized {@link Injector}s. Each InjectorShell corresponds to either the top-level root
+ * injector, or a private child injector.
+ *
+ * <p>The root InjectorShell extracts elements from its list of modules and processes these elements
+ * to aggregate data that is used to populate its injector's fields. Child injectors are constructed
+ * similarly, but using {@link PrivateElements} instead of modules.
+ *
+ * <p>It is necessary to create the root and child injectors in a single batch because there can be
+ * bidirectional parent <-> child injector dependencies that require the entire tree of injectors to
+ * be initialized together in the {@link InternalInjectorCreator}.
+ *
  */
 final class InjectorShell {
 
@@ -47,48 +61,19 @@ final class InjectorShell {
         return elements;
     }
 
-
-    /**
-     * The Injector is a special case because we allow both parent and child injectors to both have
-     * a binding for that key.
-     */
-    private static void bindInjector(InjectorImpl injector) {
-        Key<Injector> key = Key.get(Injector.class);
-        InjectorFactory injectorFactory = new InjectorFactory(injector);
-        injector.state.putBinding(key,
-                new ProviderInstanceBindingImpl<>(injector, key, SourceProvider.UNKNOWN_SOURCE,
-                        injectorFactory, Scoping.UNSCOPED, injectorFactory,
-                        ImmutableSet.of()));
-    }
-
-    private static void bindStage(InjectorImpl injector, Stage stage) {
-        Key<Stage> key = Key.get(Stage.class);
-        InstanceBindingImpl<Stage> stageBinding = new InstanceBindingImpl<>(
-                injector,
-                key,
-                SourceProvider.UNKNOWN_SOURCE,
-                new ConstantFactory<>(Initializables.of(stage)),
-                ImmutableSet.of(),
-                stage);
-        injector.state.putBinding(key, stageBinding);
-    }
-
     static class Builder {
         private final List<Element> elements = Lists.newArrayList();
         private final List<Module> modules = Lists.newArrayList();
 
-        /**
+        // lazily constructed fields
-         * lazily constructed
+        private InjectorBindingData bindingData;
-         */
+        private InjectorJitBindingData jitBindingData;
-        private State state;
 
         private InjectorImpl parent;
         private InjectorOptions options;
         private Stage stage;
 
-        /**
+        /** null unless this exists in a {@link Binder#newPrivateBinder private environment} */
-         * null unless this exists in a {@link Binder#newPrivateBinder private environment}
-         */
         private PrivateElementsImpl privateElements;
 
         Builder stage(Stage stage) {
@@ -98,7 +83,8 @@ final class InjectorShell {
 
         Builder parent(InjectorImpl parent) {
             this.parent = parent;
-            this.state = new InheritingState(parent.state);
+            this.jitBindingData = new InjectorJitBindingData(Optional.of(parent.getJitBindingData()));
+            this.bindingData = new InjectorBindingData(Optional.of(parent.getBindingData()));
             this.options = parent.options;
             this.stage = options.stage;
             return this;
@@ -111,22 +97,24 @@ final class InjectorShell {
         }
 
         void addModules(Iterable<? extends Module> modules) {
-            if (modules != null) {
             for (Module module : modules) {
                 this.modules.add(module);
             }
         }
-        }
 
         Stage getStage() {
             return options.stage;
         }
 
-        /**
+        /** Synchronize on this before calling {@link #build}. */
-         * Synchronize on this before calling {@link #build}.
-         */
         Object lock() {
-            return getState().lock();
+            // Lazily initializes bindingData and jitBindingData, if they were not already
+            // initialized with a parent injector by {@link #parent(InjectorImpl)}.
+            if (bindingData == null) {
+                jitBindingData = new InjectorJitBindingData(Optional.empty());
+                bindingData = new InjectorBindingData(Optional.empty());
+            }
+            return jitBindingData.lock();
         }
 
         /**
@@ -136,27 +124,38 @@ final class InjectorShell {
          */
         List<InjectorShell> build(
                 Initializer initializer,
-                ProcessedBindingData bindingData,
+                ProcessedBindingData processedBindingData,
-                Stopwatch stopwatch,
+                ContinuousStopwatch stopwatch,
                 Errors errors) {
             checkState(stage != null, "Stage not initialized");
             checkState(privateElements == null || parent != null, "PrivateElements with no parent");
-            checkState(state != null, "no state. Did you remember to lock() ?");
+            checkState(bindingData != null, "no binding data. Did you remember to lock() ?");
+            checkState(
+                    (privateElements == null && elements.isEmpty()) || modules.isEmpty(),
+                    "The shell is either built from modules (root) or from PrivateElements (children).");
 
             // bind Singleton if this is a top-level injector
             if (parent == null) {
                 modules.add(0, new RootModule());
             } else {
-                modules.add(0, new InheritedScannersModule(parent.state));
+                modules.add(0, new InheritedScannersModule(parent.getBindingData()));
             }
             elements.addAll(Elements.getElements(stage, modules));
 
+            // Check binding source restrictions only for the root shell (note that the root shell
+            // can have a parent Injector, when Injector.createChildInjector is called). It isn't
+            // necessary to call this check on child PrivateElements shells because it walks the entire
+            // tree of elements, recurring on PrivateElements.
+            if (privateElements == null) {
+                elements.addAll(BindingSourceRestriction.check(GUICE_INTERNAL, elements));
+            }
+
             // Look for injector-changing options
             InjectorOptionsProcessor optionsProcessor = new InjectorOptionsProcessor(errors);
             optionsProcessor.process(null, elements);
             options = optionsProcessor.getOptions(stage, options);
 
-            InjectorImpl injector = new InjectorImpl(parent, state, options);
+            InjectorImpl injector = new InjectorImpl(parent, bindingData, jitBindingData, options);
             if (privateElements != null) {
                 privateElements.initInjector(injector);
             }
@@ -171,10 +170,11 @@ final class InjectorShell {
             new MessageProcessor(errors).process(injector, elements);
 
             new ListenerBindingProcessor(errors).process(injector, elements);
-            List<TypeListenerBinding> typeListenerBindings = injector.state.getTypeListenerBindings();
+            List<TypeListenerBinding> typeListenerBindings =
+                    injector.getBindingData().getTypeListenerBindings();
             injector.membersInjectorStore = new MembersInjectorStore(injector, typeListenerBindings);
             List<ProvisionListenerBinding> provisionListenerBindings =
-                    injector.state.getProvisionListenerBindings();
+                    injector.getBindingData().getProvisionListenerBindings();
             injector.provisionListenerStore =
                     new ProvisionListenerCallbackStore(provisionListenerBindings);
             stopwatch.resetAndLog("TypeListeners & ProvisionListener creation");
@@ -187,13 +187,13 @@ final class InjectorShell {
 
             bindStage(injector, stage);
             bindInjector(injector);
-            //bindLogger(injector);
+            bindLogger(injector);
 
             // Process all normal bindings, then UntargettedBindings.
             // This is necessary because UntargettedBindings can create JIT bindings
             // and need all their other dependencies set up ahead of time.
-            new BindingProcessor(errors, initializer, bindingData).process(injector, elements);
+            new BindingProcessor(errors, initializer, processedBindingData).process(injector, elements);
-            new UntargettedBindingProcessor(errors, bindingData).process(injector, elements);
+            new UntargettedBindingProcessor(errors, processedBindingData).process(injector, elements);
             stopwatch.resetAndLog("Binding creation");
 
             new ModuleAnnotatedMethodScannerProcessor(errors).process(injector, elements);
@@ -206,19 +206,34 @@ final class InjectorShell {
             PrivateElementProcessor processor = new PrivateElementProcessor(errors);
             processor.process(injector, elements);
             for (Builder builder : processor.getInjectorShellBuilders()) {
-                injectorShells.addAll(builder.build(initializer, bindingData, stopwatch, errors));
+                injectorShells.addAll(builder.build(initializer, processedBindingData, stopwatch, errors));
             }
             stopwatch.resetAndLog("Private environment creation");
 
             return injectorShells;
         }
 
-        private State getState() {
-            if (state == null) {
-                state = new InheritingState(State.NONE);
-            }
-            return state;
     }
+
+    /**
+     * The Injector is a special case because we allow both parent and child injectors to both have a
+     * binding for that key.
+     */
+    private static void bindInjector(InjectorImpl injector) {
+        Key<Injector> key = Key.get(Injector.class);
+        InjectorFactory injectorFactory = new InjectorFactory(injector);
+        injector
+                .getBindingData()
+                .putBinding(
+                        key,
+                        new ProviderInstanceBindingImpl<Injector>(
+                                injector,
+                                key,
+                                SourceProvider.UNKNOWN_SOURCE,
+                                injectorFactory,
+                                Scoping.UNSCOPED,
+                                injectorFactory,
+                                ImmutableSet.<InjectionPoint>of()));
     }
 
     private static class InjectorFactory implements InternalFactory<Injector>, Provider<Injector> {
@@ -238,11 +253,66 @@ final class InjectorShell {
             return injector;
         }
 
+        @Override
         public String toString() {
             return "Provider<Injector>";
         }
     }
 
+    /**
+     * The Logger is a special case because it knows the injection point of the injected member. It's
+     * the only binding that does this.
+     */
+    private static void bindLogger(InjectorImpl injector) {
+        Key<Logger> key = Key.get(Logger.class);
+        LoggerFactory loggerFactory = new LoggerFactory();
+        injector
+                .getBindingData()
+                .putBinding(
+                        key,
+                        new ProviderInstanceBindingImpl<Logger>(
+                                injector,
+                                key,
+                                SourceProvider.UNKNOWN_SOURCE,
+                                loggerFactory,
+                                Scoping.UNSCOPED,
+                                loggerFactory,
+                                ImmutableSet.<InjectionPoint>of()));
+    }
+
+    private static class LoggerFactory implements InternalFactory<Logger>, Provider<Logger> {
+        @Override
+        public Logger get(InternalContext context, Dependency<?> dependency, boolean linked) {
+            InjectionPoint injectionPoint = dependency.getInjectionPoint();
+            return injectionPoint == null
+                    ? Logger.getAnonymousLogger()
+                    : Logger.getLogger(injectionPoint.getMember().getDeclaringClass().getName());
+        }
+
+        @Override
+        public Logger get() {
+            return Logger.getAnonymousLogger();
+        }
+
+        @Override
+        public String toString() {
+            return "Provider<Logger>";
+        }
+    }
+
+    private static void bindStage(InjectorImpl injector, Stage stage) {
+        Key<Stage> key = Key.get(Stage.class);
+        InstanceBindingImpl<Stage> stageBinding =
+                new InstanceBindingImpl<Stage>(
+                        injector,
+                        key,
+                        SourceProvider.UNKNOWN_SOURCE,
+                        new ConstantFactory<Stage>(Initializables.of(stage)),
+                        ImmutableSet.<InjectionPoint>of(),
+                        stage);
+        injector.getBindingData().putBinding(key, stageBinding);
+    }
+
     private static class RootModule implements Module {
         @Override
         public void configure(Binder binder) {
@@ -253,15 +323,15 @@ final class InjectorShell {
     }
 
     private static class InheritedScannersModule implements Module {
-        private final State state;
+        private final InjectorBindingData bindingData;
 
-        InheritedScannersModule(State state) {
+        InheritedScannersModule(InjectorBindingData bindingData) {
-            this.state = state;
+            this.bindingData = bindingData;
         }
 
         @Override
         public void configure(Binder binder) {
-            for (ModuleAnnotatedMethodScannerBinding binding : state.getScannerBindings()) {
+            for (ModuleAnnotatedMethodScannerBinding binding : bindingData.getScannerBindings()) {
                 binding.applyTo(binder);
             }
         }

src/main/java/com/google/inject/internal/InternalErrorDetail.java

@@ -0,0 +1,61 @@
+package com.google.inject.internal;
+
+import com.google.common.base.CaseFormat;
+import com.google.common.collect.ImmutableSet;
+import com.google.inject.spi.ErrorDetail;
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * Represents an error created by Guice as opposed to custom error added to the binder from
+ * application code.
+ */
+abstract class InternalErrorDetail<T extends ErrorDetail<T>> extends ErrorDetail<T> {
+  // A list of errors that have help documentation.
+  private static final ImmutableSet<ErrorId> DOCUMENTED_ERRORS =
+      ImmutableSet.<ErrorId>builder()
+          .add(ErrorId.BINDING_ALREADY_SET)
+          .add(ErrorId.CAN_NOT_PROXY_CLASS)
+          .add(ErrorId.CIRCULAR_PROXY_DISABLED)
+          .add(ErrorId.DUPLICATE_BINDING_ANNOTATIONS)
+          .add(ErrorId.DUPLICATE_ELEMENT)
+          .add(ErrorId.DUPLICATE_SCOPES)
+          .add(ErrorId.ERROR_INJECTING_CONSTRUCTOR)
+          .add(ErrorId.ERROR_INJECTING_METHOD)
+          .add(ErrorId.ERROR_IN_CUSTOM_PROVIDER)
+          .add(ErrorId.INJECT_INNER_CLASS)
+          .add(ErrorId.MISSING_CONSTRUCTOR)
+          .add(ErrorId.MISSING_IMPLEMENTATION)
+          .add(ErrorId.NULL_INJECTED_INTO_NON_NULLABLE)
+          .add(ErrorId.NULL_VALUE_IN_MAP)
+          .add(ErrorId.SCOPE_NOT_FOUND)
+          .add(ErrorId.TOO_MANY_CONSTRUCTORS)
+          .build();
+
+  private static final String DOC_BASE_URL = "https://github.com/google/guice/wiki/";
+
+  protected final ErrorId errorId;
+
+  protected InternalErrorDetail(
+      ErrorId errorId, String message, List<Object> sources, Throwable cause) {
+    super(message, sources, cause);
+    this.errorId = errorId;
+  }
+
+  @Override
+  protected final Optional<String> getLearnMoreLink() {
+    if (DOCUMENTED_ERRORS.contains(errorId)) {
+      return Optional.of(DOC_BASE_URL + errorId.name());
+    }
+    return Optional.empty();
+  }
+
+  @Override
+  protected final Optional<String> getErrorIdentifier() {
+    if (errorId == ErrorId.OTHER) {
+      return Optional.empty();
+    }
+    String id = "Guice/" + CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, errorId.name());
+    return Optional.of(id);
+  }
+}

src/main/java/com/google/inject/internal/InternalFlags.java

@@ -2,20 +2,131 @@ package com.google.inject.internal;
 
 import java.security.AccessController;
 import java.security.PrivilegedAction;
+import java.util.Arrays;
+import java.util.logging.Logger;
+
+/** Contains flags for Guice. */
+public final class InternalFlags {
+    private static final Logger logger = Logger.getLogger(InternalFlags.class.getName());
+
+    private static final IncludeStackTraceOption INCLUDE_STACK_TRACES =
+            getSystemOption(
+                    "guice_include_stack_traces",
+                    IncludeStackTraceOption.ONLY_FOR_DECLARING_SOURCE);
+
+    private static final CustomClassLoadingOption CUSTOM_CLASS_LOADING =
+            getSystemOption(
+                    "guice_custom_class_loading",
+                    CustomClassLoadingOption.BRIDGE,
+                    CustomClassLoadingOption.OFF);
+
+    private static final NullableProvidesOption NULLABLE_PROVIDES =
+            getSystemOption("guice_check_nullable_provides_params", NullableProvidesOption.ERROR);
+
+    private static final BytecodeGenOption BYTECODE_GEN_OPTION =
+            getSystemOption("guice_bytecode_gen_option", BytecodeGenOption.ENABLED);
+
+    private static final ColorizeOption COLORIZE_OPTION =
+            getSystemOption("guice_colorize_error_messages", ColorizeOption.OFF);
+
+    /** The options for Guice stack trace collection. */
+    public enum IncludeStackTraceOption {
+        /** No stack trace collection */
+        OFF,
+        /**  Minimum stack trace collection (Default) */
+        ONLY_FOR_DECLARING_SOURCE,
+        /** Full stack trace for everything */
+        COMPLETE
+    }
+
+    /** The options for Guice custom class loading. */
+    public enum CustomClassLoadingOption {
+        /**
+         * Define fast/enhanced types in the same class loader as their original type, never creates
+         * class loaders. Uses Unsafe.defineAnonymousClass to gain access to existing class loaders.
+         */
+        OFF,
 
         /**
- * Contains flags for Guice.
+         * Define fast/enhanced types with Unsafe.defineAnonymousClass, never creates class loaders.
+         * This is faster than regular class loading and anonymous classes are easier to unload.
+         *
+         * <p>Note: with this option you cannot look up fast/enhanced types by name or mock/spy them.
          */
-public class InternalFlags {
+        ANONYMOUS,
 
-    private static final IncludeStackTraceOption INCLUDE_STACK_TRACES
+        /**
-            = parseIncludeStackTraceOption();
+         * Attempt to define fast/enhanced types in the same class loader as their original type.
+         * Otherwise creates a child class loader whose parent is the original class loader. (Default)
+         */
+        BRIDGE,
 
-    private static final CustomClassLoadingOption CUSTOM_CLASS_LOADING
+        /**
-            = parseCustomClassLoadingOption();
+         * Define fast/enhanced types in a child class loader whose parent is the original class loader.
+         *
+         * <p>Note: with this option you cannot intercept package-private methods.
+         */
+        CHILD
+    }
 
-    private static final NullableProvidesOption NULLABLE_PROVIDES
+    /** Options for handling nullable parameters used in provides methods. */
-            = parseNullableProvidesOption(NullableProvidesOption.ERROR);
+    public enum NullableProvidesOption {
+        /** Ignore null parameters to @Provides methods. */
+        IGNORE,
+        /** Warn if null parameters are passed to non-@Nullable parameters of provides methods. */
+        WARN,
+        /** Error if null parameters are passed to non-@Nullable parameters of provides parameters */
+        ERROR
+    }
+
+    /**
+     * Options for controlling whether Guice uses bytecode generation at runtime. When bytecode
+     * generation is enabled, the following features will be enabled in Guice:
+     *
+     * <ul>
+     *   <li>Runtime bytecode generation (instead of reflection) will be used when Guice need to
+     *       invoke application code.
+     *   <li>Method interception.
+     * </ul>
+     *
+     * <p>Bytecode generation is generally faster than using reflection when invoking application
+     * code, however, it can use more memory and slower in certain cases due to the time spent in
+     * generating the classes. If you prefer to use reflection over bytecode generation then set
+     * {@link BytecodeGenOption} to {@code DISABLED}.
+     */
+    public enum BytecodeGenOption {
+        /**
+         * Bytecode generation is disabled and using features that require it such as method
+         * interception will throw errors at run time.
+         */
+        DISABLED,
+        /** Bytecode generation is enabled. */
+        ENABLED,
+    }
+
+    /** Options for enable or disable using ansi color in error messages. */
+    public enum ColorizeOption {
+        AUTO {
+            @Override
+            boolean enabled() {
+                return System.console() != null && System.getenv("TERM") != null;
+            }
+        },
+        ON {
+            @Override
+            boolean enabled() {
+                return true;
+            }
+        },
+        OFF {
+            @Override
+            boolean enabled() {
+                return false;
+            }
+        };
+
+        abstract boolean enabled();
+    }
 
     public static IncludeStackTraceOption getIncludeStackTraceOption() {
         return INCLUDE_STACK_TRACES;
@@ -29,19 +140,12 @@ public class InternalFlags {
         return NULLABLE_PROVIDES;
     }
 
-    private static IncludeStackTraceOption parseIncludeStackTraceOption() {
+    public static boolean isBytecodeGenEnabled() {
-        return getSystemOption("guice_include_stack_traces",
+        return BYTECODE_GEN_OPTION == BytecodeGenOption.ENABLED;
-                IncludeStackTraceOption.ONLY_FOR_DECLARING_SOURCE);
     }
 
-    private static CustomClassLoadingOption parseCustomClassLoadingOption() {
+    public static boolean enableColorizeErrorMessages() {
-        return getSystemOption("guice_custom_class_loading",
+        return COLORIZE_OPTION.enabled();
-                CustomClassLoadingOption.BRIDGE, CustomClassLoadingOption.OFF);
-    }
-
-    private static NullableProvidesOption parseNullableProvidesOption(
-            NullableProvidesOption defaultValue) {
-        return getSystemOption("guice_check_nullable_provides_params", defaultValue);
     }
 
     /**
@@ -61,66 +165,31 @@ public class InternalFlags {
      * @param name of the system option
      * @param defaultValue if the option is not set
      * @param secureValue if the security manager disallows access to the option
+     *
      * @return value of the option, defaultValue if not set, secureValue if no access
      */
     private static <T extends Enum<T>> T getSystemOption(final String name, T defaultValue,
                                                          T secureValue) {
         Class<T> enumType = defaultValue.getDeclaringClass();
+        String value = null;
         try {
-            String value = AccessController.doPrivileged((PrivilegedAction<String>) ()
+            value =
-                    -> System.getProperty(name));
+                    AccessController.doPrivileged(
+                            new PrivilegedAction<String>() {
+                                @Override
+                                public String run() {
+                                    return System.getProperty(name);
+                                }
+                            });
             return (value != null && value.length() > 0) ? Enum.valueOf(enumType, value) : defaultValue;
         } catch (SecurityException e) {
             return secureValue;
         } catch (IllegalArgumentException e) {
+            logger.warning(value + " is not a valid flag value for " + name + ". "
+                    + " Values must be one of " + Arrays.asList(enumType.getEnumConstants()));
             return defaultValue;
         }
     }
 
-    /**
+    private InternalFlags() {}
-     * The options for Guice stack trace collection.
-     */
-    public enum IncludeStackTraceOption {
-        /**
-         * No stack trace collection
-         */
-        OFF,
-        /**
-         * Minimum stack trace collection (Default)
-         */
-        ONLY_FOR_DECLARING_SOURCE,
-        /**
-         * Full stack trace for everything
-         */
-        COMPLETE
-    }
-
-    /**
-     * The options for Guice custom class loading.
-     */
-    public enum CustomClassLoadingOption {
-        /**
-         * No custom class loading
-         */
-        OFF,
-        /**
-         * Automatically bridge between class loaders (Default)
-         */
-        BRIDGE
-    }
-
-    public enum NullableProvidesOption {
-        /**
-         * Ignore null parameters to @Provides methods.
-         */
-        IGNORE,
-        /**
-         * Warn if null parameters are passed to non-@Nullable parameters of provides methods.
-         */
-        WARN,
-        /**
-         * Error if null parameters are passed to non-@Nullable parameters of provides parameters
-         */
-        ERROR
-    }
 }

src/main/java/com/google/inject/internal/InternalInjectorCreator.java

@@ -1,5 +1,6 @@
 package com.google.inject.internal;
 
+import com.google.common.base.Stopwatch;
 import com.google.inject.Binding;
 import com.google.inject.Injector;
 import com.google.inject.Key;
@@ -9,12 +10,11 @@ import com.google.inject.Provider;
 import com.google.inject.Scope;
 import com.google.inject.Stage;
 import com.google.inject.TypeLiteral;
-import com.google.inject.internal.util.Stopwatch;
+import com.google.inject.internal.util.ContinuousStopwatch;
 import com.google.inject.spi.Dependency;
 import com.google.inject.spi.Element;
 import com.google.inject.spi.InjectionPoint;
 import com.google.inject.spi.TypeConverterBinding;
-
 import java.lang.annotation.Annotation;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -28,24 +28,28 @@ import java.util.Set;
  * top-level injector.
  *
  * <p>Injector construction happens in two phases.
+ *
  * <ol>
  *   <li>Static building. In this phase, we interpret commands, create bindings, and inspect
- * dependencies. During this phase, we hold a lock to ensure consistency with parent injectors.
+ *       dependencies. During this phase, we hold a lock to ensure consistency with parent
- * No user code is executed in this phase.</li>
+ *       injectors. No user code is executed in this phase.
  *   <li>Dynamic injection. In this phase, we call user code. We inject members that requested
  *       injection. This may require user's objects be created and their providers be called. And we
- * create eager singletons. In this phase, user code may have started other threads. This phase
+ *       create eager singletons. In this phase, user code may have started other threads. This
- * is not executed for injectors created using {@link Stage#TOOL the tool stage}</li>
+ *       phase is not executed for injectors created using {@link Stage#TOOL the tool stage}
  * </ol>
  *
+ * @author crazybob@google.com (Bob Lee)
+ * @author jessewilson@google.com (Jesse Wilson)
  */
 public final class InternalInjectorCreator {
 
-    private final Stopwatch stopwatch = new Stopwatch();
+    private final ContinuousStopwatch stopwatch =
+            new ContinuousStopwatch(Stopwatch.createUnstarted());
     private final Errors errors = new Errors();
 
     private final Initializer initializer = new Initializer();
-    private final ProcessedBindingData bindingData;
+    private final ProcessedBindingData processedBindingData;
     private final InjectionRequestProcessor injectionRequestProcessor;
 
     private final InjectorShell.Builder shellBuilder = new InjectorShell.Builder();
@@ -53,7 +57,7 @@ public final class InternalInjectorCreator {
 
     public InternalInjectorCreator() {
         injectionRequestProcessor = new InjectionRequestProcessor(errors, initializer);
-        bindingData = new ProcessedBindingData();
+        processedBindingData = new ProcessedBindingData();
     }
 
     public InternalInjectorCreator stage(Stage stage) {
@@ -63,9 +67,10 @@ public final class InternalInjectorCreator {
 
     /**
      * Sets the parent of the injector to-be-constructed. As a side effect, this sets this injector's
-     * stage to the stage of {@code parent}.
+     * stage to the stage of {@code parent} and sets {@link #requireExplicitBindings()} if the parent
+     * injector also required them.
      */
-    InternalInjectorCreator parentInjector(InjectorImpl parent) {
+    public InternalInjectorCreator parentInjector(InjectorImpl parent) {
         shellBuilder.parent(parent);
         return this;
     }
@@ -76,11 +81,14 @@ public final class InternalInjectorCreator {
     }
 
     public Injector build() {
+        if (shellBuilder == null) {
+            throw new AssertionError("Already built, builders are not reusable.");
+        }
 
-        // Synchronize while we're building up the bindings and other injector state. This ensures that
+        // Synchronize while we're building up the bindings and other injector data. This ensures that
         // the JIT bindings in the parent injector don't change while we're being built
         synchronized (shellBuilder.lock()) {
-            shells = shellBuilder.build(initializer, bindingData, stopwatch, errors);
+            shells = shellBuilder.build(initializer, processedBindingData, stopwatch, errors);
             stopwatch.resetAndLog("Injector construction");
 
             initializeStatically();
@@ -97,44 +105,49 @@ public final class InternalInjectorCreator {
         }
     }
 
-    /**
+    /** Initialize and validate everything. */
-     * Initialize and validate everything.
-     */
     private void initializeStatically() {
-        bindingData.initializeBindings();
+        processedBindingData.initializeBindings();
         stopwatch.resetAndLog("Binding initialization");
+
         for (InjectorShell shell : shells) {
-            shell.getInjector().index();
+            shell.getInjector().getBindingData().indexBindingsByType();
         }
         stopwatch.resetAndLog("Binding indexing");
+
         injectionRequestProcessor.process(shells);
         stopwatch.resetAndLog("Collecting injection requests");
-        bindingData.runCreationListeners(errors);
+
+        processedBindingData.runCreationListeners(errors);
         stopwatch.resetAndLog("Binding validation");
+
         injectionRequestProcessor.validate();
         stopwatch.resetAndLog("Static validation");
+
         initializer.validateOustandingInjections(errors);
         stopwatch.resetAndLog("Instance member validation");
+
         new LookupProcessor(errors).process(shells);
         for (InjectorShell shell : shells) {
             ((DeferredLookups) shell.getInjector().lookups).initialize(errors);
         }
         stopwatch.resetAndLog("Provider verification");
+
         // This needs to come late since some user bindings rely on requireBinding calls to create
         // jit bindings during the LookupProcessor.
-        bindingData.initializeDelayedBindings();
+        processedBindingData.initializeDelayedBindings();
         stopwatch.resetAndLog("Delayed Binding initialization");
+
         for (InjectorShell shell : shells) {
             if (!shell.getElements().isEmpty()) {
                 throw new AssertionError("Failed to execute " + shell.getElements());
             }
         }
+
         errors.throwCreationExceptionIfErrorsExist();
     }
 
-    /**
+    /** Returns the injector being constructed. This is not necessarily the root injector. */
-     * Returns the injector being constructed. This is not necessarily the root injector.
-     */
     private Injector primaryInjector() {
         return shells.get(0).getInjector();
     }
@@ -166,28 +179,29 @@ public final class InternalInjectorCreator {
      * while we're binding these singletons are not be eager.
      */
     void loadEagerSingletons(InjectorImpl injector, Stage stage, final Errors errors) {
+        List<BindingImpl<?>> candidateBindings = new ArrayList<>();
         @SuppressWarnings("unchecked") // casting Collection<Binding> to Collection<BindingImpl> is safe
         Collection<BindingImpl<?>> bindingsAtThisLevel =
-                (Collection) injector.state.getExplicitBindingsThisLevel().values();
+                (Collection) injector.getBindingData().getExplicitBindingsThisLevel().values();
-        List<BindingImpl<?>> candidateBindings = new ArrayList<>(bindingsAtThisLevel);
+        candidateBindings.addAll(bindingsAtThisLevel);
-        synchronized (injector.state.lock()) {
+        synchronized (injector.getJitBindingData().lock()) {
             // jit bindings must be accessed while holding the lock.
-            candidateBindings.addAll(injector.jitBindings.values());
+            candidateBindings.addAll(injector.getJitBindingData().getJitBindings().values());
         }
-        try (InternalContext context = injector.enterContext()) {
+        InternalContext context = injector.enterContext();
+        try {
             for (BindingImpl<?> binding : candidateBindings) {
                 if (isEagerSingleton(injector, binding, stage)) {
                     Dependency<?> dependency = Dependency.get(binding.getKey());
-                    Dependency<?> previous = context.pushDependency(dependency, binding.getSource());
                     try {
                         binding.getInternalFactory().get(context, dependency, false);
                     } catch (InternalProvisionException e) {
                         errors.withSource(dependency).merge(e);
+                    }
+                }
+            }
         } finally {
-                        context.popStateAndSetDependency(previous);
+            context.close();
-                    }
-                }
-            }
         }
     }
 
@@ -201,16 +215,14 @@ public final class InternalInjectorCreator {
         // bindings. This only applies if the linked binding is not itself scoped.
         if (binding instanceof LinkedBindingImpl) {
             Key<?> linkedBinding = ((LinkedBindingImpl<?>) binding).getLinkedKey();
-            return binding.getScoping().isNoScope() &&
+            return binding.getScoping().isNoScope()
-                    isEagerSingleton(injector, injector.getBinding(linkedBinding), stage);
+                    && isEagerSingleton(injector, injector.getBinding(linkedBinding), stage);
         }
 
         return false;
     }
 
-    /**
+    /** {@link Injector} exposed to users in {@link Stage#TOOL}. */
-     * {@link Injector} exposed to users in {@link Stage#TOOL}.
-     */
     static class ToolStageInjector implements Injector {
         private final Injector delegateInjector;
 

src/main/java/com/google/inject/internal/InternalProvisionException.java

@@ -48,74 +48,89 @@ import java.util.logging.Logger;
  * #errorInUserCode} is called with an exception that holds multiple errors (like
  * ProvisionException).
  */
-@SuppressWarnings("serial")
 public final class InternalProvisionException extends Exception {
-
     private static final Logger logger = Logger.getLogger(Guice.class.getName());
-
     private static final Set<Dependency<?>> warnedDependencies =
-      Collections.newSetFromMap(new ConcurrentHashMap<>());
+            Collections.newSetFromMap(new ConcurrentHashMap<Dependency<?>, Boolean>());
 
 
     public static InternalProvisionException circularDependenciesDisabled(Class<?> expectedType) {
         return create(
+                ErrorId.CIRCULAR_PROXY_DISABLED,
                 "Found a circular dependency involving %s, and circular dependencies are disabled.",
                 expectedType);
     }
 
     public static InternalProvisionException cannotProxyClass(Class<?> expectedType) {
         return create(
+                ErrorId.CAN_NOT_PROXY_CLASS,
                 "Tried proxying %s to support a circular dependency, but it is not an interface.",
                 expectedType);
     }
 
-  public static InternalProvisionException create(String format, Object... arguments) {
+    public static InternalProvisionException create(
-    return new InternalProvisionException(Messages.create(format, arguments));
+            ErrorId errorId, String format, Object... arguments) {
+        return new InternalProvisionException(Messages.create(errorId, format, arguments));
     }
 
     public static InternalProvisionException errorInUserCode(
-      Throwable cause, String messageFormat, Object... arguments) {
+            ErrorId errorId, Throwable cause, String messageFormat, Object... arguments) {
         Collection<Message> messages = Errors.getMessagesFromThrowable(cause);
         if (!messages.isEmpty()) {
             // TODO(lukes): it seems like we are dropping some valuable context here..
             // consider eliminating this special case
             return new InternalProvisionException(messages);
         } else {
-      return new InternalProvisionException(Messages.create(cause, messageFormat, arguments));
+            return new InternalProvisionException(
+                    Messages.create(errorId, cause, messageFormat, arguments));
         }
     }
 
     public static InternalProvisionException subtypeNotProvided(
             Class<? extends javax.inject.Provider<?>> providerType, Class<?> type) {
-    return create("%s doesn't provide instances of %s.", providerType, type);
+        return create(
+                ErrorId.SUBTYPE_NOT_PROVIDED, "%s doesn't provide instances of %s.", providerType, type);
     }
 
     public static InternalProvisionException errorInProvider(Throwable cause) {
-    return errorInUserCode(cause, "Error in custom provider, %s", cause);
+        return errorInUserCode(ErrorId.ERROR_IN_CUSTOM_PROVIDER, cause, "%s", cause);
     }
 
     public static InternalProvisionException errorInjectingMethod(Throwable cause) {
-    return errorInUserCode(cause, "Error injecting method, %s", cause);
+        return errorInUserCode(ErrorId.ERROR_INJECTING_METHOD, cause, "%s", cause);
     }
 
     public static InternalProvisionException errorInjectingConstructor(Throwable cause) {
-    return errorInUserCode(cause, "Error injecting constructor, %s", cause);
+        return errorInUserCode(ErrorId.ERROR_INJECTING_CONSTRUCTOR, cause, "%s", cause);
     }
 
     public static InternalProvisionException errorInUserInjector(
             MembersInjector<?> listener, TypeLiteral<?> type, RuntimeException cause) {
         return errorInUserCode(
-        cause, "Error injecting %s using %s.%n Reason: %s", type, listener, cause);
+                ErrorId.ERROR_IN_USER_INJECTOR,
+                cause,
+                "Error injecting %s using %s.%n Reason: %s",
+                type,
+                listener,
+                cause);
     }
 
     public static InternalProvisionException jitDisabled(Key<?> key) {
-    return create("Explicit bindings are required and %s is not explicitly bound.", key);
+        return create(
+                ErrorId.JIT_DISABLED,
+                "Explicit bindings are required and %s is not explicitly bound.",
+                key);
     }
 
     public static InternalProvisionException errorNotifyingInjectionListener(
             InjectionListener<?> listener, TypeLiteral<?> type, RuntimeException cause) {
         return errorInUserCode(
-        cause, "Error notifying InjectionListener %s of %s.%n Reason: %s", listener, type, cause);
+                ErrorId.OTHER,
+                cause,
+                "Error notifying InjectionListener %s of %s.%n Reason: %s",
+                listener,
+                type,
+                cause);
     }
 
     /**
@@ -142,7 +157,8 @@ public final class InternalProvisionException extends Exception {
                                             + " Use -Dguice_check_nullable_provides_params=ERROR to turn this into an"
                                             + " error.",
                                     new Object[] {
-                    Messages.formatParameter(dependency), Messages.convert(dependency.getKey())
+                                            SourceFormatter.getParameterName(dependency),
+                                            Messages.convert(dependency.getKey())
                                     });
                         }
                         return;
@@ -150,20 +166,26 @@ public final class InternalProvisionException extends Exception {
             }
         }
 
+        String parameterName =
+                (dependency.getParameterIndex() != -1) ? SourceFormatter.getParameterName(dependency) : "";
+        Object memberStackTraceElement =
+                StackTraceElements.forMember(dependency.getInjectionPoint().getMember());
         Object formattedDependency =
-        (dependency.getParameterIndex() != -1)
+                parameterName.isEmpty()
-            ? Messages.formatParameter(dependency)
+                        ? memberStackTraceElement
-            : StackTraceElements.forMember(dependency.getInjectionPoint().getMember());
+                        : "the " + parameterName + " of " + memberStackTraceElement;
-
         throw InternalProvisionException.create(
-            "null returned by binding at %s%n but %s is not @Nullable", source, formattedDependency)
+                ErrorId.NULL_INJECTED_INTO_NON_NULLABLE,
+                "null returned by binding at %s%n but %s is not @Nullable",
+                source,
+                formattedDependency)
                 .addSource(source);
     }
 
     private final List<Object> sourcesToPrepend = new ArrayList<>();
     private final ImmutableList<Message> errors;
 
-  private InternalProvisionException(Message error) {
+    InternalProvisionException(Message error) {
         this(ImmutableList.of(error));
     }
 
@@ -211,6 +233,7 @@ public final class InternalProvisionException extends Exception {
 
     /** Returns this exception convered to a ProvisionException. */
     public ProvisionException toProvisionException() {
-    return new ProvisionException(getErrors());
+        ProvisionException exception = new ProvisionException(getErrors());
+        return exception;
     }
 }

src/main/java/com/google/inject/internal/ListenerBindingProcessor.java

@@ -14,13 +14,13 @@ final class ListenerBindingProcessor extends AbstractProcessor {
 
     @Override
     public Boolean visit(TypeListenerBinding binding) {
-        injector.state.addTypeListener(binding);
+        injector.getBindingData().addTypeListener(binding);
         return true;
     }
 
     @Override
     public Boolean visit(ProvisionListenerBinding binding) {
-        injector.state.addProvisionListener(binding);
+        injector.getBindingData().addProvisionListener(binding);
         return true;
     }
 }

src/main/java/com/google/inject/internal/Messages.java

@@ -1,39 +1,30 @@
 package com.google.inject.internal;
 
-import static com.google.common.base.Preconditions.checkArgument;
+import static java.util.stream.Collectors.joining;
+
 import com.google.common.base.Equivalence;
 import com.google.common.base.Objects;
 import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.inject.Key;
-import com.google.inject.TypeLiteral;
 import com.google.inject.internal.util.Classes;
-import com.google.inject.internal.util.StackTraceElements;
-import com.google.inject.spi.Dependency;
 import com.google.inject.spi.ElementSource;
-import com.google.inject.spi.InjectionPoint;
+import com.google.inject.spi.ErrorDetail;
 import com.google.inject.spi.Message;
-import java.lang.reflect.Field;
 import java.lang.reflect.Member;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Formatter;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
 
-/**
+/** Utility methods for {@link Message} objects */
- * Utility methods for {@link Message} objects
- */
 public final class Messages {
+    private Messages() {}
 
-    private Messages() {
+    /** Prepends the list of sources to the given {@link Message} */
-    }
-
-    /**
-     * Prepends the list of sources to the given {@link Message}
-     */
     static Message mergeSources(List<Object> sources, Message message) {
         List<Object> messageSources = message.getSources();
         // It is possible that the end of getSources() and the beginning of message.getSources() are
@@ -41,12 +32,13 @@ public final class Messages {
         // most likely scenario where this would happen is when a scoped binding throws an exception,
         // due to the fact that InternalFactoryToProviderAdapter applies the binding source when
         // merging errors.
-        if (!sources.isEmpty() && !messageSources.isEmpty() &&
+        if (!sources.isEmpty()
-                Objects.equal(messageSources.get(0), sources.get(sources.size() - 1))) {
+                && !messageSources.isEmpty()
+                && Objects.equal(messageSources.get(0), sources.get(sources.size() - 1))) {
             messageSources = messageSources.subList(1, messageSources.size());
         }
-        return new Message(ImmutableList.builder().addAll(sources).addAll(messageSources).build(),
+        return message.withSource(
-                message.getMessage(), message.getCause());
+                ImmutableList.builder().addAll(sources).addAll(messageSources).build());
     }
 
     /**
@@ -60,30 +52,33 @@ public final class Messages {
         return String.format(messageFormat, arguments);
     }
 
-    /**
+    /** Returns the formatted message for an exception with the specified messages. */
-     * Returns the formatted message for an exception with the specified messages.
-     */
     public static String formatMessages(String heading, Collection<Message> errorMessages) {
         Formatter fmt = new Formatter().format(heading).format(":%n%n");
         int index = 1;
         boolean displayCauses = getOnlyCause(errorMessages) == null;
 
+        List<ErrorDetail<?>> remainingErrors =
+                errorMessages.stream().map(Message::getErrorDetail).collect(Collectors.toList());
+
         Map<Equivalence.Wrapper<Throwable>, Integer> causes = Maps.newHashMap();
-        for (Message errorMessage : errorMessages) {
+        while (!remainingErrors.isEmpty()) {
-            int thisIdx = index++;
+            ErrorDetail<?> currentError = remainingErrors.get(0);
-            fmt.format("%s) %s%n", thisIdx, errorMessage.getMessage());
+            // Split the remaining errors into 2 groups, one that contains mergeable errors with
+            // currentError and the other that need to be formatted separately in the next iteration.
+            Map<Boolean, List<ErrorDetail<?>>> partitionedByMergeable =
+                    remainingErrors.subList(1, remainingErrors.size()).stream()
+                            .collect(Collectors.partitioningBy(currentError::isMergeable));
 
-            List<Object> dependencies = errorMessage.getSources();
+            remainingErrors = partitionedByMergeable.get(false);
-            for (int i = dependencies.size() - 1; i >= 0; i--) {
-                Object source = dependencies.get(i);
-                formatSource(fmt, source);
-            }
 
-            Throwable cause = errorMessage.getCause();
+            currentError.format(index, partitionedByMergeable.get(true), fmt);
+
+            Throwable cause = currentError.getCause();
             if (displayCauses && cause != null) {
                 Equivalence.Wrapper<Throwable> causeEquivalence = ThrowableEquivalence.INSTANCE.wrap(cause);
                 if (!causes.containsKey(causeEquivalence)) {
-                    causes.put(causeEquivalence, thisIdx);
+                    causes.put(causeEquivalence, index);
                     fmt.format("Caused by: %s", Throwables.getStackTraceAsString(cause));
                 } else {
                     int causeIdx = causes.get(causeEquivalence);
@@ -92,57 +87,64 @@ public final class Messages {
                             cause.getClass().getName(), causeIdx);
                 }
             }
-
             fmt.format("%n");
+            index++;
         }
 
-        if (errorMessages.size() == 1) {
+        if (index == 2) {
             fmt.format("1 error");
         } else {
-            fmt.format("%s errors", errorMessages.size());
+            fmt.format("%s errors", index - 1);
         }
 
-        return fmt.toString();
+        return PackageNameCompressor.compressPackagesInMessage(fmt.toString());
     }
 
     /**
      * Creates a new Message without a cause.
      *
+     * @param errorId The enum id for the error
      * @param messageFormat Format string
      * @param arguments format string arguments
      */
-    public static Message create(String messageFormat, Object... arguments) {
+    public static Message create(ErrorId errorId, String messageFormat, Object... arguments) {
-        return create(null, messageFormat, arguments);
+        return create(errorId, null, messageFormat, arguments);
     }
 
     /**
      * Creates a new Message with the given cause.
      *
+     * @param errorId The enum id for the error
      * @param cause The exception that caused the error
      * @param messageFormat Format string
      * @param arguments format string arguments
      */
-    public static Message create(Throwable cause, String messageFormat, Object... arguments) {
+    public static Message create(
-        return create(cause, ImmutableList.of(), messageFormat, arguments);
+            ErrorId errorId, Throwable cause, String messageFormat, Object... arguments) {
+        return create(errorId, cause, ImmutableList.of(), messageFormat, arguments);
     }
 
     /**
      * Creates a new Message with the given cause and a binding source stack.
      *
+     * @param errorId The enum id for the error
      * @param cause The exception that caused the error
      * @param sources The binding sources for the source stack
      * @param messageFormat Format string
      * @param arguments format string arguments
      */
-    public static Message create(Throwable cause, List<Object> sources, String messageFormat, Object... arguments) {
+    public static Message create(
+            ErrorId errorId,
+            Throwable cause,
+            List<Object> sources,
+            String messageFormat,
+            Object... arguments) {
         String message = format(messageFormat, arguments);
-        return new Message(sources, message, cause);
+        return new Message(errorId, sources, message, cause);
     }
 
-    /**
+    /** Formats an object in a user friendly way. */
-     * Formats an object in a user friendly way.
+    static Object convert(Object o) {
-     */
-    public static Object convert(Object o) {
         ElementSource source = null;
         if (o instanceof ElementSource) {
             source = (ElementSource) o;
@@ -151,7 +153,7 @@ public final class Messages {
         return convert(o, source);
     }
 
-    public static Object convert(Object o, ElementSource source) {
+    static Object convert(Object o, ElementSource source) {
         for (Converter<?> converter : converters) {
             if (converter.appliesTo(o)) {
                 return appendModules(converter.convert(o), source);
@@ -161,145 +163,11 @@ public final class Messages {
     }
 
     private static Object appendModules(Object source, ElementSource elementSource) {
-        String modules = moduleSourceString(elementSource);
+        String modules = SourceFormatter.getModuleStack(elementSource);
         if (modules.length() == 0) {
             return source;
         } else {
-            return source + modules;
+            return source + " (installed by: " + modules + ")";
-        }
-    }
-
-    private static String moduleSourceString(ElementSource elementSource) {
-        // if we only have one module (or don't know what they are), then don't bother
-        // reporting it, because the source already is going to report exactly that module.
-        if (elementSource == null) {
-            return "";
-        }
-        List<String> modules = Lists.newArrayList(elementSource.getModuleClassNames());
-        // Insert any original element sources w/ module info into the path.
-        while (elementSource.getOriginalElementSource() != null) {
-            elementSource = elementSource.getOriginalElementSource();
-            modules.addAll(0, elementSource.getModuleClassNames());
-        }
-        if (modules.size() <= 1) {
-            return "";
-        }
-
-        // Ideally we'd do:
-        //    return Joiner.on(" -> ")
-        //        .appendTo(new StringBuilder(" (via modules: "), Lists.reverse(modules))
-        //        .append(")").toString();
-        // ... but for some reason we can't find Lists.reverse, so do it the boring way.
-        StringBuilder builder = new StringBuilder(" (via modules: ");
-        for (int i = modules.size() - 1; i >= 0; i--) {
-            builder.append(modules.get(i));
-            if (i != 0) {
-                builder.append(" -> ");
-            }
-        }
-        builder.append(")");
-        return builder.toString();
-    }
-
-    static void formatSource(Formatter formatter, Object source) {
-        ElementSource elementSource = null;
-        if (source instanceof ElementSource) {
-            elementSource = (ElementSource) source;
-            source = elementSource.getDeclaringSource();
-        }
-        formatSource(formatter, source, elementSource);
-    }
-
-    static void formatSource(Formatter formatter, Object source, ElementSource elementSource) {
-        String modules = moduleSourceString(elementSource);
-        if (source instanceof Dependency) {
-            Dependency<?> dependency = (Dependency<?>) source;
-            InjectionPoint injectionPoint = dependency.getInjectionPoint();
-            if (injectionPoint != null) {
-                formatInjectionPoint(formatter, dependency, injectionPoint, elementSource);
-            } else {
-                formatSource(formatter, dependency.getKey(), elementSource);
-            }
-
-        } else if (source instanceof InjectionPoint) {
-            formatInjectionPoint(formatter, null, (InjectionPoint) source, elementSource);
-
-        } else if (source instanceof Class) {
-            formatter.format("  at %s%s%n", StackTraceElements.forType((Class<?>) source), modules);
-
-        } else if (source instanceof Member) {
-            formatter.format("  at %s%s%n", StackTraceElements.forMember((Member) source), modules);
-
-        } else if (source instanceof TypeLiteral) {
-            formatter.format("  while locating %s%s%n", source, modules);
-
-        } else if (source instanceof Key) {
-            Key<?> key = (Key<?>) source;
-            formatter.format("  while locating %s%n", convert(key, elementSource));
-
-        } else if (source instanceof Thread) {
-            formatter.format("  in thread %s%n", source);
-
-        } else {
-            formatter.format("  at %s%s%n", source, modules);
-        }
-    }
-
-    private static void formatInjectionPoint(
-            Formatter formatter,
-            Dependency<?> dependency,
-            InjectionPoint injectionPoint,
-            ElementSource elementSource) {
-        Member member = injectionPoint.getMember();
-        Class<? extends Member> memberType = Classes.memberType(member);
-
-        if (memberType == Field.class) {
-            dependency = injectionPoint.getDependencies().get(0);
-            formatter.format("  while locating %s%n", convert(dependency.getKey(), elementSource));
-            formatter.format("    for field at %s%n", StackTraceElements.forMember(member));
-
-        } else if (dependency != null) {
-            formatter.format("  while locating %s%n", convert(dependency.getKey(), elementSource));
-            formatter.format("    for %s%n", formatParameter(dependency));
-
-        } else {
-            formatSource(formatter, injectionPoint.getMember());
-        }
-    }
-
-    static String formatParameter(Dependency<?> dependency) {
-        int ordinal = dependency.getParameterIndex() + 1;
-        return String.format(
-                "the %s%s parameter of %s",
-                ordinal,
-                getOrdinalSuffix(ordinal),
-                StackTraceElements.forMember(dependency.getInjectionPoint().getMember()));
-    }
-
-    /**
-     * Maps {@code 1} to the string {@code "1st"} ditto for all non-negative numbers
-     *
-     * @see <a href="https://en.wikipedia.org/wiki/English_numerals#Ordinal_numbers">
-     * https://en.wikipedia.org/wiki/English_numerals#Ordinal_numbers</a>
-     */
-    private static String getOrdinalSuffix(int ordinal) {
-        // negative ordinals don't make sense, we allow zero though because we are programmers
-        checkArgument(ordinal >= 0);
-        if ((ordinal / 10) % 10 == 1) {
-            // all the 'teens' are weird
-            return "th";
-        } else {
-            // could use a lookup table? any better?
-            switch (ordinal % 10) {
-                case 1:
-                    return "st";
-                case 2:
-                    return "nd";
-                case 3:
-                    return "rd";
-                default:
-                    return "th";
-            }
         }
     }
 
@@ -322,22 +190,22 @@ public final class Messages {
         abstract String toString(T t);
     }
 
-    @SuppressWarnings({"rawtypes"}) // rawtypes aren't avoidable
+    @SuppressWarnings({"unchecked", "rawtypes"}) // rawtypes aren't avoidable
     private static final Collection<Converter<?>> converters =
             ImmutableList.of(
-                    new Converter<>(Class.class) {
+                    new Converter<Class>(Class.class) {
                         @Override
                         public String toString(Class c) {
                             return c.getName();
                         }
                     },
-                    new Converter<>(Member.class) {
+                    new Converter<Member>(Member.class) {
                         @Override
                         public String toString(Member member) {
                             return Classes.toString(member);
                         }
                     },
-                    new Converter<>(Key.class) {
+                    new Converter<Key>(Key.class) {
                         @Override
                         public String toString(Key key) {
                             if (key.getAnnotationType() != null) {
@@ -388,4 +256,46 @@ public final class Messages {
             return Objects.hashCode(t.getClass().hashCode(), t.getMessage(), hash(t.getCause()));
         }
     }
+
+    private enum FormatOptions {
+        RED("\u001B[31m"),
+        BOLD("\u001B[1m"),
+        FAINT("\u001B[2m"),
+        ITALIC("\u001B[3m"),
+        UNDERLINE("\u001B[4m"),
+        RESET("\u001B[0m");
+
+        private final String ansiCode;
+
+        FormatOptions(String ansiCode) {
+            this.ansiCode = ansiCode;
+        }
+    }
+
+    private static final String formatText(String text, FormatOptions... options) {
+        if (!InternalFlags.enableColorizeErrorMessages()) {
+            return text;
+        }
+        return String.format(
+                "%s%s%s",
+                Arrays.stream(options).map(option -> option.ansiCode).collect(joining()),
+                text,
+                FormatOptions.RESET.ansiCode);
+    }
+
+    public static final String bold(String text) {
+        return formatText(text, FormatOptions.BOLD);
+    }
+
+    public static final String redBold(String text) {
+        return formatText(text, FormatOptions.RED, FormatOptions.BOLD);
+    }
+
+    public static final String underline(String text) {
+        return formatText(text, FormatOptions.UNDERLINE);
+    }
+
+    public static final String faint(String text) {
+        return formatText(text, FormatOptions.FAINT);
+    }
 }

src/main/java/com/google/inject/internal/MissingConstructorError.java

@@ -0,0 +1,82 @@
+package com.google.inject.internal;
+
+import com.google.common.base.Objects;
+import com.google.common.collect.Lists;
+import com.google.inject.TypeLiteral;
+import com.google.inject.spi.ErrorDetail;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Modifier;
+import java.util.ArrayList;
+import java.util.Formatter;
+import java.util.List;
+
+/** Error reported when Guice can't find an useable constructor to create objects. */
+final class MissingConstructorError extends InternalErrorDetail<MissingConstructorError> {
+    private final TypeLiteral<?> type;
+    private final boolean atInjectRequired;
+
+    MissingConstructorError(TypeLiteral<?> type, boolean atInjectRequired, List<Object> sources) {
+        super(
+                ErrorId.MISSING_CONSTRUCTOR,
+                "No injectable constructor for type " + type + ".",
+                sources,
+                null);
+        this.type = type;
+        this.atInjectRequired = atInjectRequired;
+    }
+
+    @Override
+    public boolean isMergeable(ErrorDetail<?> other) {
+        if (other instanceof MissingConstructorError) {
+            MissingConstructorError otherMissing = (MissingConstructorError) other;
+            return Objects.equal(type, otherMissing.type)
+                    && Objects.equal(atInjectRequired, otherMissing.atInjectRequired);
+        }
+        return false;
+    }
+
+    @Override
+    protected void formatDetail(List<ErrorDetail<?>> mergeableErrors, Formatter formatter) {
+        formatter.format("%n");
+        Class<?> rawType = type.getRawType();
+        if (atInjectRequired) {
+            formatter.format(
+                    "Injector is configured to require @Inject constructors but %s does not have a @Inject"
+                            + " annotated constructor.%n",
+                    rawType);
+        } else {
+            Constructor<?> noArgConstructor = null;
+            try {
+                noArgConstructor = type.getRawType().getDeclaredConstructor();
+            } catch (NoSuchMethodException e) {
+                // Ignore
+            }
+            if (noArgConstructor == null) {
+                formatter.format(
+                        "%s does not have a @Inject annotated constructor or a no-arg constructor.%n", rawType);
+            } else if (Modifier.isPrivate(noArgConstructor.getModifiers())
+                    && !Modifier.isPrivate(rawType.getModifiers())) {
+                formatter.format(
+                        "%s has a private no-arg constructor but the class is not private. Guice can only use"
+                                + " a private no-arg constructor if it is defined in a private class.%n",
+                        rawType);
+            }
+        }
+        formatter.format("%n");
+
+        List<List<Object>> sourcesList = new ArrayList<>();
+        sourcesList.add(getSources());
+        mergeableErrors.forEach(error -> sourcesList.add(error.getSources()));
+
+        formatter.format("%s%n", Messages.bold("Requested by:"));
+        int sourceListIndex = 1;
+        for (List<Object> sources : sourcesList) {
+            ErrorFormatter.formatSources(sourceListIndex++, Lists.reverse(sources), formatter);
+        }
+    }
+
+    @Override
+    public MissingConstructorError withSources(List<Object> newSources) {
+        return new MissingConstructorError(type, atInjectRequired, newSources);
+    }
+}

src/main/java/com/google/inject/internal/MissingImplementationError.java

@@ -0,0 +1,75 @@
+package com.google.inject.internal;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Lists;
+import com.google.inject.Injector;
+import com.google.inject.Key;
+import com.google.inject.spi.ErrorDetail;
+import java.util.ArrayList;
+import java.util.Formatter;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/** Error reported by Guice when a key is not bound in the injector. */
+final class MissingImplementationError<T>
+        extends InternalErrorDetail<MissingImplementationError<T>> {
+
+    private final Key<T> key;
+    private final ImmutableList<String> suggestions;
+
+    public MissingImplementationError(Key<T> key, Injector injector, List<Object> sources) {
+        this(key, MissingImplementationErrorHints.getSuggestions(key, injector), sources);
+    }
+
+    private MissingImplementationError(
+            Key<T> key, ImmutableList<String> suggestions, List<Object> sources) {
+        super(
+                ErrorId.MISSING_IMPLEMENTATION,
+                String.format("No implementation for %s was bound.", Messages.convert(key)),
+                sources,
+                null);
+        this.key = key;
+        this.suggestions = suggestions;
+    }
+
+    @Override
+    public boolean isMergeable(ErrorDetail<?> otherError) {
+        return otherError instanceof MissingImplementationError
+                && ((MissingImplementationError) otherError).key.equals(this.key);
+    }
+
+    @Override
+    public void formatDetail(List<ErrorDetail<?>> mergeableErrors, Formatter formatter) {
+        if (!suggestions.isEmpty()) {
+            suggestions.forEach(formatter::format);
+        }
+        List<List<Object>> sourcesList = new ArrayList<>();
+        sourcesList.add(getSources());
+        sourcesList.addAll(
+                mergeableErrors.stream().map(ErrorDetail::getSources).collect(Collectors.toList()));
+
+        List<List<Object>> filteredSourcesList =
+                sourcesList.stream()
+                        .map(this::trimSource)
+                        .filter(sources -> !sources.isEmpty())
+                        .collect(Collectors.toList());
+
+        if (!filteredSourcesList.isEmpty()) {
+            formatter.format("%n%s%n", Messages.bold("Requested by:"));
+            int sourceListIndex = 1;
+            for (List<Object> sources : filteredSourcesList) {
+                ErrorFormatter.formatSources(sourceListIndex++, Lists.reverse(sources), formatter);
+            }
+        }
+    }
+
+    @Override
+    public MissingImplementationError<T> withSources(List<Object> newSources) {
+        return new MissingImplementationError<T>(key, suggestions, newSources);
+    }
+
+    /** Omit the key itself in the source list since the information is redundant. */
+    private List<Object> trimSource(List<Object> sources) {
+        return sources.stream().filter(source -> !source.equals(this.key)).collect(Collectors.toList());
+    }
+}

src/main/java/com/google/inject/internal/MissingImplementationErrorHints.java

@@ -0,0 +1,113 @@
+package com.google.inject.internal;
+
+import static java.lang.Math.min;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.primitives.Primitives;
+import com.google.inject.Binding;
+import com.google.inject.Injector;
+import com.google.inject.Key;
+import com.google.inject.TypeLiteral;
+import com.google.inject.spi.BindingSourceRestriction;
+import java.util.ArrayList;
+import java.util.Formatter;
+import java.util.List;
+import java.util.Map;
+
+// TODO(b/165344346): Migrate to use suggest hints API.
+/** Helper class to find hints for {@link MissingImplementationError}. */
+final class MissingImplementationErrorHints {
+
+  private MissingImplementationErrorHints() {}
+
+  /** When a binding is not found, show at most this many bindings with the same type */
+  private static final int MAX_MATCHING_TYPES_REPORTED = 3;
+
+  /** When a binding is not found, show at most this many bindings that have some similarities */
+  private static final int MAX_RELATED_TYPES_REPORTED = 3;
+
+  /**
+   * If the key is unknown and it is one of these types, it generally means there is a missing
+   * annotation.
+   */
+  private static final ImmutableSet<Class<?>> COMMON_AMBIGUOUS_TYPES =
+      ImmutableSet.<Class<?>>builder()
+          .add(Object.class)
+          .add(String.class)
+          .addAll(Primitives.allWrapperTypes())
+          .build();
+
+  static <T> ImmutableList<String> getSuggestions(Key<T> key, Injector injector) {
+    ImmutableList.Builder<String> suggestions = ImmutableList.builder();
+    TypeLiteral<T> type = key.getTypeLiteral();
+
+    BindingSourceRestriction.getMissingImplementationSuggestion(GuiceInternal.GUICE_INTERNAL, key)
+        .ifPresent(suggestions::add);
+
+    // Keys which have similar strings as the desired key
+    List<String> possibleMatches = new ArrayList<>();
+    List<Binding<T>> sameTypes = injector.findBindingsByType(type);
+    if (!sameTypes.isEmpty()) {
+      suggestions.add("%nDid you mean?");
+      int howMany = min(sameTypes.size(), MAX_MATCHING_TYPES_REPORTED);
+      for (int i = 0; i < howMany; ++i) {
+        // TODO: Look into a better way to prioritize suggestions. For example, possbily
+        // use levenshtein distance of the given annotation vs actual annotation.
+        suggestions.add(Messages.format("%n    * %s", sameTypes.get(i).getKey()));
+      }
+      int remaining = sameTypes.size() - MAX_MATCHING_TYPES_REPORTED;
+      if (remaining > 0) {
+        String plural = (remaining == 1) ? "" : "s";
+        suggestions.add(
+            Messages.format("%n    %d more binding%s with other annotations.", remaining, plural));
+      }
+      suggestions.add("%n");
+    } else {
+      // For now, do a simple substring search for possibilities. This can help spot
+      // issues when there are generics being used (such as a wrapper class) and the
+      // user has forgotten they need to bind based on the wrapper, not the underlying
+      // class. In the future, consider doing a strict in-depth type search.
+      // TODO: Look into a better way to prioritize suggestions. For example, possbily
+      // use levenshtein distance of the type literal strings.
+      String want = type.toString();
+      Map<Key<?>, Binding<?>> bindingMap = injector.getAllBindings();
+      for (Key<?> bindingKey : bindingMap.keySet()) {
+        String have = bindingKey.getTypeLiteral().toString();
+        if (have.contains(want) || want.contains(have)) {
+          Formatter fmt = new Formatter();
+          fmt.format("%s bound ", Messages.convert(bindingKey));
+          new SourceFormatter(
+                  bindingMap.get(bindingKey).getSource(), fmt, /* omitPreposition= */ false)
+              .format();
+          possibleMatches.add(fmt.toString());
+          // TODO: Consider a check that if there are more than some number of results,
+          // don't suggest any.
+          if (possibleMatches.size() > MAX_RELATED_TYPES_REPORTED) {
+            // Early exit if we have found more than we need.
+            break;
+          }
+        }
+      }
+
+      if (!possibleMatches.isEmpty() && (possibleMatches.size() <= MAX_RELATED_TYPES_REPORTED)) {
+        suggestions.add("%nDid you mean?");
+        for (String possibleMatch : possibleMatches) {
+          suggestions.add(Messages.format("%n    %s", possibleMatch));
+        }
+      }
+    }
+
+    // If where are no possibilities to suggest, then handle the case of missing
+    // annotations on simple types. This is usually a bad idea.
+    if (sameTypes.isEmpty()
+        && possibleMatches.isEmpty()
+        && key.getAnnotationType() == null
+        && COMMON_AMBIGUOUS_TYPES.contains(key.getTypeLiteral().getRawType())) {
+      // We don't recommend using such simple types without annotations.
+      suggestions.add("%nThe key seems very generic, did you forget an annotation?");
+    }
+
+    return suggestions.build();
+  }
+}

src/main/java/com/google/inject/internal/ModuleAnnotatedMethodScannerProcessor.java

@@ -4,6 +4,7 @@ import com.google.inject.spi.ModuleAnnotatedMethodScannerBinding;
 
 /**
  * Handles {@code Binder.scanModulesForAnnotatedMethods} commands.
+ *
  */
 final class ModuleAnnotatedMethodScannerProcessor extends AbstractProcessor {
 
@@ -13,7 +14,7 @@ final class ModuleAnnotatedMethodScannerProcessor extends AbstractProcessor {
 
     @Override
     public Boolean visit(ModuleAnnotatedMethodScannerBinding command) {
-        injector.state.addScanner(command);
+        injector.getBindingData().addScanner(command);
         return true;
     }
 }

src/main/java/com/google/inject/internal/PackageNameCompressor.java

@@ -0,0 +1,237 @@
+package com.google.inject.internal;
+
+import static java.util.Comparator.comparing;
+
+import com.google.common.base.Joiner;
+import com.google.common.base.Splitter;
+import com.google.common.base.Strings;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Ordering;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+
+/**
+ * Munges an error message to remove/shorten package names and adds a legend at the end.
+ */
+final class PackageNameCompressor {
+
+    static final String LEGEND_HEADER =
+            "\n\n======================\nFull classname legend:\n======================\n";
+    static final String LEGEND_FOOTER =
+            "========================\nEnd of classname legend:\n========================\n";
+
+    private static final ImmutableSet<String> PACKAGES_SKIPPED_IN_LEGEND = ImmutableSet.of(
+            "java.lang.",
+            "java.util.");
+
+    private static final Splitter PACKAGE_SPLITTER = Splitter.on('.');
+
+    private static final Joiner PACKAGE_JOINER = Joiner.on('.');
+
+    // TODO(erichang): Consider validating this regex by also passing in all of the known types from
+    // keys, module names, component names, etc and checking against that list. This may have some
+    // extra complications with taking apart types like List<Foo> to get the inner class names.
+    private static final Pattern CLASSNAME_PATTERN =
+            // Match lowercase package names with trailing dots. Start with a non-word character so we
+            // don't match substrings in like Bar.Foo and match the com.foo.Foo. Require at least 2
+            // package names to avoid matching non package names like a sentence ending with a period and
+            // starting with an upper case letter without space, for example:
+            // foo.Must in message "Invalid value for foo.Must not be empty." should not be compressed.
+            // Start a group to not include the non-word character.
+            Pattern.compile(
+                    "[\\W](([a-z_0-9]++[.]){2,}+"
+                            // Then match a name starting with an uppercase letter. This is the outer class name.
+                            + "[A-Z][\\w$]*)");
+
+    // Pattern used to filter out quoted strings that should not have their package name compressed.
+    // Picked '"' here because Guice uses it when including a string literal in an error message. This
+    // will allow user to include class names in the error message and disable the compressor by
+    // putting the name in a pair of '"'.
+    // The pattern without the escapes: ([^"]+)((")?[^"\r\n]*")?
+    // First group captures non quoted strings
+    // Second group captures either a single quote or a string with a pair of quotes within a line
+    // Class names in second group will not be compressed.
+    private static final Pattern QUOTED_PATTERN =
+            Pattern.compile("([^\\\"]+)((\\\")?[^\\\"\\r\\n]*\\\")?");
+
+    /**
+     * Compresses an error message by stripping the packages out of class names and adding them
+     * to a legend at the bottom of the error.
+     */
+    static String compressPackagesInMessage(String input) {
+        Matcher matcher = CLASSNAME_PATTERN.matcher(input);
+
+        Set<String> names = new HashSet<>();
+        // Find all classnames in the error. Note that if our regex isn't complete, it just means the
+        // classname is left in the full form, which is a fine fallback.
+        while (matcher.find()) {
+            String name = matcher.group(1);
+            names.add(name);
+        }
+        // Now dedupe any conflicts. Use a TreeMap since we're going to need the legend sorted anyway.
+        // This map is from short name to full name.
+        Map<String, String> replacementMap = shortenNames(names);
+
+        // If we have nothing to replace, just return the original.
+        if (replacementMap.isEmpty()) {
+            return input;
+        }
+
+        StringBuilder output = new StringBuilder();
+        Set<String> replacedShortNames = replaceFullNames(input, replacementMap, output);
+        if (replacedShortNames.isEmpty()) {
+            return input;
+        }
+
+        String classNameLegend =
+                buildClassNameLegend(Maps.filterKeys(replacementMap, replacedShortNames::contains));
+        return output.append(classNameLegend).toString();
+    }
+
+    /**
+     * Replaces full class names in {@code input} and append the replaced content to {@code output}
+     * and then returns a set of short names that were used as replacement.
+     *
+     * <p>String literals that are quoted in the {@code input} will be added to the {@code output}
+     * unchanged. So any full class name that only appear in the string literal will not be included
+     * in the returned short names set.
+     */
+    private static ImmutableSet<String> replaceFullNames(
+            String input, Map<String, String> replacementMap, StringBuilder output) {
+        ImmutableSet.Builder<String> replacedShortNames = ImmutableSet.builder();
+        // Sort short names in reverse alphabetical order. This is necessary so that a short name that
+        // has a prefix that is another short name will be replaced first, otherwise the longer name
+        // will not be collected as one of the replacedShortNames.
+        List<String> shortNames =
+                replacementMap.keySet().stream()
+                        .sorted(Ordering.natural().reverse())
+                        .collect(Collectors.toList());
+        Matcher matcher = QUOTED_PATTERN.matcher(input);
+        while (matcher.find()) {
+            String replaced = matcher.group(1);
+            for (String shortName : shortNames) {
+                String fullName = replacementMap.get(shortName);
+                int beforeLen = replaced.length();
+                replaced = replaced.replace(fullName, shortName);
+                // If the replacement happened then put the short name in replacedShortNames.
+                // Only values in replacedShortNames are included in the full class name legend.
+                if (replaced.length() < beforeLen) {
+                    replacedShortNames.add(shortName);
+                }
+            }
+            output.append(replaced);
+            String quoted = matcher.group(2);
+            if (quoted != null) {
+                output.append(quoted);
+            }
+        }
+        return replacedShortNames.build();
+    }
+
+    private static String buildClassNameLegend(Map<String, String> replacementMap) {
+        StringBuilder legendBuilder = new StringBuilder();
+        // Find the longest key for building the legend
+        int longestKey = replacementMap.keySet().stream().max(comparing(String::length)).get().length();
+        for (Map.Entry<String, String> entry : replacementMap.entrySet()) {
+            String shortName = entry.getKey();
+            String fullName = entry.getValue();
+            // Skip certain prefixes. We need to check the shortName for a . though in case
+            // there was some type of conflict like java.util.concurrent.Future and
+            // java.util.foo.Future that got shortened to concurrent.Future and foo.Future.
+            // In those cases we do not want to skip the legend. We only skip if the class
+            // is directly in that package.
+            String prefix = fullName.substring(0, fullName.length() - shortName.length());
+            if (PACKAGES_SKIPPED_IN_LEGEND.contains(prefix) && !shortName.contains(".")) {
+                continue;
+            }
+
+            // Add to the legend
+            legendBuilder
+                    .append(shortName)
+                    .append(": ")
+                    // Add enough spaces to adjust the columns
+                    .append(Strings.repeat(" ", longestKey - shortName.length()))
+                    // Surround the full class name with quotes to avoid them getting compressed again if
+                    // the error is wrapped inside another Guice error.
+                    .append('"')
+                    .append(fullName)
+                    .append('"')
+                    .append("\n");
+        }
+
+        return legendBuilder.length() == 0
+                ? ""
+                : Messages.bold(LEGEND_HEADER)
+                + Messages.faint(legendBuilder.toString())
+                + Messages.bold(LEGEND_FOOTER);
+    }
+
+    /**
+     * Returns a map from short name to full name after resolving conflicts. This resolves conflicts
+     * by adding on segments of the package name until they are unique. For example, com.foo.Baz and
+     * com.bar.Baz will conflict on Baz and then resolve with foo.Baz and bar.Baz as replacements.
+     */
+    private static Map<String, String> shortenNames(Collection<String> names) {
+        HashMultimap<String, List<String>> shortNameToPartsMap = HashMultimap.create();
+        for (String name : names) {
+            List<String> parts = new ArrayList<>(PACKAGE_SPLITTER.splitToList(name));
+            // Start with the just the class name as the simple name
+            String className = parts.remove(parts.size() - 1);
+            shortNameToPartsMap.put(className, parts);
+        }
+
+        // Iterate through looking for conflicts adding the next part of the package until there are no
+        // more conflicts
+        while (true) {
+            // Save the keys with conflicts to avoid concurrent modification issues
+            List<String> conflictingShortNames = new ArrayList<>();
+            for (Map.Entry<String, Collection<List<String>>> entry
+                    : shortNameToPartsMap.asMap().entrySet()) {
+                if (entry.getValue().size() > 1) {
+                    conflictingShortNames.add(entry.getKey());
+                }
+            }
+
+            if (conflictingShortNames.isEmpty()) {
+                break;
+            }
+
+            // For all conflicts, add in the next part of the package
+            for (String conflictingShortName : conflictingShortNames) {
+                Set<List<String>> partsCollection = shortNameToPartsMap.removeAll(conflictingShortName);
+                for (List<String> parts : partsCollection) {
+                    String newShortName = parts.remove(parts.size() - 1) + "." + conflictingShortName;
+                    // If we've removed the last part of the package, then just skip it entirely because
+                    // now we're not shortening it at all.
+                    if (!parts.isEmpty()) {
+                        shortNameToPartsMap.put(newShortName, parts);
+                    }
+                }
+            }
+        }
+
+        // Turn the multimap into a regular map now that conflicts have been resolved. Use a TreeMap
+        // since we're going to need the legend sorted anyway. This map is from short name to full name.
+        Map<String, String> replacementMap = new TreeMap<>();
+        for (Map.Entry<String, Collection<List<String>>> entry
+                : shortNameToPartsMap.asMap().entrySet()) {
+            replacementMap.put(
+                    entry.getKey(),
+                    PACKAGE_JOINER.join(Iterables.getOnlyElement(entry.getValue())) + "." + entry.getKey());
+        }
+        return replacementMap;
+    }
+
+    private PackageNameCompressor() {}
+}

src/main/java/com/google/inject/internal/ProviderMethodsModule.java

@@ -1,5 +1,9 @@
 package com.google.inject.internal;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.base.Objects;
 import com.google.common.collect.HashMultimap;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -13,7 +17,6 @@ import com.google.inject.spi.InjectionPoint;
 import com.google.inject.spi.Message;
 import com.google.inject.spi.ModuleAnnotatedMethodScanner;
 import com.google.inject.util.Modules;
-
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
@@ -22,49 +25,38 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
-import static com.google.common.base.Preconditions.checkNotNull;
-import static com.google.common.base.Preconditions.checkState;
-
 /**
  * Creates bindings to methods annotated with {@literal @}{@link Provides}. Use the scope and
  * binding annotations on the provider method to configure the binding.
  *
  */
 public final class ProviderMethodsModule implements Module {
-
     private final Object delegate;
-
     private final TypeLiteral<?> typeLiteral;
-
     private final boolean skipFastClassGeneration;
-
     private final ModuleAnnotatedMethodScanner scanner;
 
-    private ProviderMethodsModule(Object delegate, boolean skipFastClassGeneration,
+    private ProviderMethodsModule(
-                                  ModuleAnnotatedMethodScanner scanner) {
+            Object delegate, boolean skipFastClassGeneration, ModuleAnnotatedMethodScanner scanner) {
         this.delegate = checkNotNull(delegate, "delegate");
-        this.typeLiteral = TypeLiteral.get(this.delegate.getClass());
+        this.typeLiteral = TypeLiteral.get(getDelegateModuleClass());
         this.skipFastClassGeneration = skipFastClassGeneration;
         this.scanner = scanner;
     }
 
-    /**
+    /** Returns a module which creates bindings for provider methods from the given module. */
-     * Returns a module which creates bindings for provider methods from the given module.
-     */
     public static Module forModule(Module module) {
         return forObject(module, false, ProvidesMethodScanner.INSTANCE);
     }
 
-    /**
+    /** Returns a module which creates bindings methods in the module that match the scanner. */
-     * Returns a module which creates bindings methods in the module that match the scanner.
-     */
     public static Module forModule(Object module, ModuleAnnotatedMethodScanner scanner) {
         return forObject(module, false, scanner);
     }
 
     /**
-     * Returns a module which creates bindings for provider methods from the given object.
+     * Returns a module which creates bindings for provider methods from the given object. This is
-     * This is useful notably for <a href="http://code.google.com/p/google-gin/">GIN</a>
+     * useful notably for <a href="http://code.google.com/p/google-gin/">GIN</a>
      *
      * <p>This will skip bytecode generation for provider methods, since it is assumed that callers
      * are only interested in Module metadata.
@@ -73,12 +65,13 @@ public final class ProviderMethodsModule implements Module {
         return forObject(object, true, ProvidesMethodScanner.INSTANCE);
     }
 
-    private static Module forObject(Object object, boolean skipFastClassGeneration,
+    private static Module forObject(
-                                    ModuleAnnotatedMethodScanner scanner) {
+            Object object, boolean skipFastClassGeneration, ModuleAnnotatedMethodScanner scanner) {
         // avoid infinite recursion, since installing a module always installs itself
         if (object instanceof ProviderMethodsModule) {
             return Modules.EMPTY_MODULE;
         }
+
         return new ProviderMethodsModule(object, skipFastClassGeneration, scanner);
     }
 
@@ -86,6 +79,10 @@ public final class ProviderMethodsModule implements Module {
         return isStaticModule() ? (Class<?>) delegate : delegate.getClass();
     }
 
+    private boolean isStaticModule() {
+        return delegate instanceof Class;
+    }
+
     @Override
     public void configure(Binder binder) {
         for (ProviderMethod<?> providerMethod : getProviderMethods(binder)) {
@@ -93,14 +90,6 @@ public final class ProviderMethodsModule implements Module {
         }
     }
 
-    private boolean isStaticModule() {
-        return delegate instanceof Class;
-    }
-
-    public Object getDelegateModule() {
-        return delegate;
-    }
-
     public List<ProviderMethod<?>> getProviderMethods(Binder binder) {
         List<ProviderMethod<?>> result = null;
         List<MethodAndAnnotation> methodsAndAnnotations = null;
@@ -196,6 +185,16 @@ public final class ProviderMethodsModule implements Module {
         return result;
     }
 
+    private static class MethodAndAnnotation {
+        final Method method;
+        final Annotation annotation;
+
+        MethodAndAnnotation(Method method, Annotation annotation) {
+            this.method = method;
+            this.annotation = annotation;
+        }
+    }
+
     /** Returns the annotation that is claimed by the scanner, or null if there is none. */
     private Annotation getAnnotation(Binder binder, Method method) {
         if (method.isBridge() || method.isSynthetic()) {
@@ -218,30 +217,7 @@ public final class ProviderMethodsModule implements Module {
         return annotation;
     }
 
-    @Override
+    private static final class Signature {
-    public boolean equals(Object o) {
-        return o instanceof ProviderMethodsModule
-                && ((ProviderMethodsModule) o).delegate == delegate
-                && ((ProviderMethodsModule) o).scanner == scanner;
-    }
-
-    @Override
-    public int hashCode() {
-        return delegate.hashCode();
-    }
-
-    private static class MethodAndAnnotation {
-        final Method method;
-        final Annotation annotation;
-
-        MethodAndAnnotation(Method method, Annotation annotation) {
-            this.method = method;
-            this.annotation = annotation;
-        }
-    }
-
-
-    private static class Signature {
         final Class<?>[] parameters;
         final String name;
         final int hashCode;
@@ -277,7 +253,6 @@ public final class ProviderMethodsModule implements Module {
         }
     }
 
-
     /** Returns true if a overrides b, assumes that the signatures match */
     private static boolean overrides(Method a, Method b) {
         // See JLS section 8.4.8.1
@@ -302,28 +277,27 @@ public final class ProviderMethodsModule implements Module {
         @SuppressWarnings("unchecked") // Define T as the method's return type.
         TypeLiteral<T> returnType = (TypeLiteral<T>) typeLiteral.getReturnType(method);
         Key<T> key = getKey(errors, returnType, method, method.getAnnotations());
+        boolean prepareMethodError = false;
         try {
             key = scanner.prepareMethod(binder, annotation, key, point);
         } catch (Throwable t) {
+            prepareMethodError = true;
             binder.addError(t);
         }
 
         if (Modifier.isAbstract(method.getModifiers())) {
             checkState(
-                    key == null,
+                    prepareMethodError || key == null,
                     "%s returned a non-null key (%s) for %s. prepareMethod() must return null for abstract"
                             + " methods",
                     scanner,
                     key,
                     method);
             return null;
-        } else {
+        }
-            checkState(
+
-                    key != null,
+        if (key == null) { // scanner returned null. Skipping the binding.
-                    "%s returned a null key for %s. prepareMethod() can only return null for abstract"
+            return null;
-                            + " methods",
-                    scanner,
-                    method);
         }
 
         Class<? extends Annotation> scopeAnnotation =
@@ -335,7 +309,7 @@ public final class ProviderMethodsModule implements Module {
         return ProviderMethod.create(
                 key,
                 method,
-                isStaticModule() ? null : delegate,
+                isStaticModule() || Modifier.isStatic(method.getModifiers()) ? null : delegate,
                 ImmutableSet.copyOf(point.getDependencies()),
                 scopeAnnotation,
                 skipFastClassGeneration,
@@ -347,4 +321,24 @@ public final class ProviderMethodsModule implements Module {
         return bindingAnnotation == null ? Key.get(type) : Key.get(type, bindingAnnotation);
     }
 
+    @Override
+    public boolean equals(Object o) {
+        return o instanceof ProviderMethodsModule
+                && ((ProviderMethodsModule) o).delegate == delegate
+                && ((ProviderMethodsModule) o).scanner.equals(scanner);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(delegate, scanner);
+    }
+
+    /** Is it scanning the built-in @Provides* methods. */
+    public boolean isScanningBuiltInProvidesMethods() {
+        return scanner == ProvidesMethodScanner.INSTANCE;
+    }
+
+    public ModuleAnnotatedMethodScanner getScanner() {
+        return scanner;
+    }
 }

src/main/java/com/google/inject/internal/ProvisionListenerStackCallback.java

@@ -4,7 +4,6 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Sets;
 import com.google.inject.Binding;
 import com.google.inject.spi.ProvisionListener;
-
 import java.util.List;
 import java.util.Set;
 
@@ -23,6 +22,11 @@ final class ProvisionListenerStackCallback<T> {
     private final ProvisionListener[] listeners;
     private final Binding<T> binding;
 
+    @SuppressWarnings("unchecked")
+    public static <T> ProvisionListenerStackCallback<T> emptyListener() {
+        return (ProvisionListenerStackCallback<T>) EMPTY_CALLBACK;
+    }
+
     public ProvisionListenerStackCallback(Binding<T> binding, List<ProvisionListener> listeners) {
         this.binding = binding;
         if (listeners.isEmpty()) {
@@ -33,18 +37,13 @@ final class ProvisionListenerStackCallback<T> {
         }
     }
 
-    @SuppressWarnings("unchecked")
-    public static <T> ProvisionListenerStackCallback<T> emptyListener() {
-        return (ProvisionListenerStackCallback<T>) EMPTY_CALLBACK;
-    }
-
     public boolean hasListeners() {
         return listeners.length > 0;
     }
 
     public T provision(InternalContext context, ProvisionCallback<T> callable)
             throws InternalProvisionException {
-        Provision provision = new Provision(context, callable);
+        Provision provision = new Provision(callable);
         RuntimeException caught = null;
         try {
             provision.provision();
@@ -58,6 +57,7 @@ final class ProvisionListenerStackCallback<T> {
             Object listener =
                     provision.erredListener != null ? provision.erredListener.getClass() : "(unknown)";
             throw InternalProvisionException.errorInUserCode(
+                    ErrorId.OTHER,
                     caught,
                     "Error notifying ProvisionListener %s of %s.%n Reason: %s",
                     listener,
@@ -70,21 +70,18 @@ final class ProvisionListenerStackCallback<T> {
 
     // TODO(sameb): Can this be more InternalFactory-like?
     public interface ProvisionCallback<T> {
-        T call() throws InternalProvisionException;
+        public T call() throws InternalProvisionException;
     }
 
     private class Provision extends ProvisionListener.ProvisionInvocation<T> {
-
-        final InternalContext context;
         final ProvisionCallback<T> callable;
         int index = -1;
         T result;
         InternalProvisionException exceptionDuringProvision;
         ProvisionListener erredListener;
 
-        public Provision(InternalContext context, ProvisionCallback<T> callable) {
+        public Provision(ProvisionCallback<T> callable) {
             this.callable = callable;
-            this.context = context;
         }
 
         @Override

src/main/java/com/google/inject/internal/RealMapBinder.java

@@ -38,6 +38,7 @@ import com.google.inject.spi.ProviderInstanceBinding;
 import com.google.inject.spi.ProviderWithExtensionVisitor;
 import com.google.inject.util.Types;
 import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
 import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -297,7 +298,7 @@ public final class RealMapBinder<K, V> implements Module {
 
         // Binds a Map<K, Provider<V>>
         RealProviderMapProvider<K, V> providerMapProvider =
-                new RealProviderMapProvider<K, V>(bindingSelection);
+                new RealProviderMapProvider<>(bindingSelection);
         binder.bind(bindingSelection.getProviderMapKey()).toProvider(providerMapProvider);
 
         // The map this exposes is internally an ImmutableMap, so it's OK to massage
@@ -309,7 +310,12 @@ public final class RealMapBinder<K, V> implements Module {
         binder.bind(bindingSelection.getJavaxProviderMapKey()).toProvider(javaxProviderMapProvider);
 
         RealMapProvider<K, V> mapProvider = new RealMapProvider<>(bindingSelection);
-        binder.bind(bindingSelection.getMapKey()).toProvider(mapProvider);
+        // Bind Map<K, V> to the provider w/ extension support.
+        binder
+                .bind(bindingSelection.getMapKey())
+                .toProvider(new ExtensionRealMapProvider<>(mapProvider));
+        // Bind Map<K, ? extends V> to the provider w/o the extension support.
+        binder.bind(bindingSelection.getMapOfKeyExtendsValueKey()).toProvider(mapProvider);
 
         // The Map.Entries are all ProviderMapEntry instances which do not allow setValue, so it is
         // safe to massage the return type like this
@@ -364,6 +370,7 @@ public final class RealMapBinder<K, V> implements Module {
         private Key<Map<K, Collection<Provider<V>>>> providerCollectionMultimapKey;
         private Key<Map<K, Collection<javax.inject.Provider<V>>>> javaxProviderCollectionMultimapKey;
         private Key<Set<Map.Entry<K, javax.inject.Provider<V>>>> entrySetJavaxProviderKey;
+        private Key<Map<K, ? extends V>> mapOfKeyExtendsValueKey;
 
         private final RealMultibinder<Map.Entry<K, Provider<V>>> entrySetBinder;
 
@@ -485,7 +492,7 @@ public final class RealMapBinder<K, V> implements Module {
             // we don't build up this data structure
             if (duplicates != null) {
                 initializationState = InitializationState.HAS_ERRORS;
-                reportDuplicateKeysError(duplicates, errors);
+                reportDuplicateKeysError(mapKey, duplicates, errors);
 
                 return false;
             }
@@ -509,26 +516,9 @@ public final class RealMapBinder<K, V> implements Module {
         }
 
         private static <K, V> void reportDuplicateKeysError(
-                Multimap<K, Binding<V>> duplicates, Errors errors) {
+                Key<Map<K, V>> mapKey, Multimap<K, Binding<V>> duplicates, Errors errors) {
-            StringBuilder sb = new StringBuilder("Map injection failed due to duplicated key ");
+            errors.duplicateMapKey(mapKey, duplicates);
-            boolean first = true;
+            return;
-            for (Map.Entry<K, Collection<Binding<V>>> entry : duplicates.asMap().entrySet()) {
-                K dupKey = entry.getKey();
-
-                if (first) {
-                    first = false;
-                    sb.append("\"").append(dupKey).append("\", from bindings:\n");
-                } else {
-                    sb.append("\n and key: \"").append(dupKey).append("\", from bindings:\n");
-                }
-
-                for (Binding<V> dup : entry.getValue()) {
-                    sb.append("\t at ").append(Messages.convert(dup.getSource())).append("\n");
-                }
-            }
-
-            // TODO(user): Add a different error for every duplicated key
-            errors.addMessage(sb.toString());
         }
 
         private boolean containsElement(Element element) {
@@ -553,6 +543,7 @@ public final class RealMapBinder<K, V> implements Module {
                     || key.equals(getJavaxProviderCollectionMultimapKey())
                     || key.equals(entrySetBinder.getSetKey())
                     || key.equals(getEntrySetJavaxProviderKey())
+                    || key.equals(getMapOfKeyExtendsValueKey())
                     || matchesValueKey(key);
         }
 
@@ -638,6 +629,19 @@ public final class RealMapBinder<K, V> implements Module {
             return local;
         }
 
+        @SuppressWarnings("unchecked")
+        private Key<Map<K, ? extends V>> getMapOfKeyExtendsValueKey() {
+            Key<Map<K, ? extends V>> local = mapOfKeyExtendsValueKey;
+            if (local == null) {
+                Type extendsValue = Types.subtypeOf(valueType.getType());
+                Type mapOfKeyAndExtendsValue = Types.mapOf(keyType.getType(), extendsValue);
+                local =
+                        mapOfKeyExtendsValueKey =
+                                (Key<Map<K, ? extends V>>) mapKey.ofType(mapOfKeyAndExtendsValue);
+            }
+            return local;
+        }
+
         private ImmutableMap<K, Binding<V>> getMapBindings() {
             checkConfiguration(isInitialized(), "MapBinder has not yet been initialized");
             return mapBindings;
@@ -727,24 +731,23 @@ public final class RealMapBinder<K, V> implements Module {
     }
 
     private static final class RealMapProvider<K, V>
-            extends RealMapBinderProviderWithDependencies<K, V, Map<K, V>>
+            extends RealMapBinderProviderWithDependencies<K, V, Map<K, V>> {
-            implements ProviderWithExtensionVisitor<Map<K, V>>, MapBinderBinding<Map<K, V>> {
+        Set<Dependency<?>> dependencies = RealMapBinder.MODULE_DEPENDENCIES;
-        private Set<Dependency<?>> dependencies = RealMapBinder.MODULE_DEPENDENCIES;
 
         /**
          * An array of all the injectors.
          *
          * <p>This is parallel to array of keys below
          */
-        private SingleParameterInjector<V>[] injectors;
+        SingleParameterInjector<V>[] injectors;
 
-        private K[] keys;
+        K[] keys;
 
-        private RealMapProvider(BindingSelection<K, V> bindingSelection) {
+        RealMapProvider(BindingSelection<K, V> bindingSelection) {
             super(bindingSelection);
         }
 
-        private BindingSelection<K, V> getBindingSelection() {
+        BindingSelection<K, V> getBindingSelection() {
             return bindingSelection;
         }
 
@@ -805,6 +808,42 @@ public final class RealMapBinder<K, V> implements Module {
         public Set<Dependency<?>> getDependencies() {
             return dependencies;
         }
+    }
+
+    /**
+     * Implementation of a provider instance for the map that also exposes details about the MapBinder
+     * using the extension SPI, delegating to another provider instance for non-extension (e.g, the
+     * actual provider instance info) data.
+     */
+    private static final class ExtensionRealMapProvider<K, V>
+            extends RealMapBinderProviderWithDependencies<K, V, Map<K, V>>
+            implements ProviderWithExtensionVisitor<Map<K, V>>, MapBinderBinding<Map<K, V>> {
+        final RealMapProvider<K, V> delegate;
+
+        ExtensionRealMapProvider(RealMapProvider<K, V> delegate) {
+            super(delegate.bindingSelection);
+            this.delegate = delegate;
+        }
+
+        BindingSelection<K, V> getBindingSelection() {
+            return bindingSelection;
+        }
+
+        @Override
+        protected void doInitialize(InjectorImpl injector, Errors errors) throws ErrorsException {
+            delegate.doInitialize(injector, errors);
+        }
+
+        @Override
+        protected Map<K, V> doProvision(InternalContext context, Dependency<?> dependency)
+                throws InternalProvisionException {
+            return delegate.doProvision(context, dependency);
+        }
+
+        @Override
+        public Set<Dependency<?>> getDependencies() {
+            return delegate.getDependencies();
+        }
 
         @Override
         @SuppressWarnings("unchecked")
@@ -831,7 +870,8 @@ public final class RealMapBinder<K, V> implements Module {
                     (Key<?>) bindingSelection.getJavaxProviderSetMultimapKey(),
                     (Key<?>) bindingSelection.getProviderCollectionMultimapKey(),
                     (Key<?>) bindingSelection.getJavaxProviderCollectionMultimapKey(),
-                    (Key<?>) bindingSelection.getMultimapKey());
+                    (Key<?>) bindingSelection.getMultimapKey(),
+                    (Key<?>) bindingSelection.getMapOfKeyExtendsValueKey());
         }
 
         @Override
@@ -925,18 +965,18 @@ public final class RealMapBinder<K, V> implements Module {
 
                 if (!keysOnlyFromBindings.isEmpty()) {
                     sb.append(
-                            Messages.format("%nFound these Bindings that were missing an associated entry:%n"));
+                            Errors.format("%nFound these Bindings that were missing an associated entry:%n"));
                     for (Key<V> key : keysOnlyFromBindings) {
                         sb.append(
-                                Messages.format("  %s bound at: %s%n", key, valueKeyToBinding.get(key).getSource()));
+                                Errors.format("  %s bound at: %s%n", key, valueKeyToBinding.get(key).getSource()));
                     }
                 }
 
                 if (!keysOnlyFromProviderMapEntrys.isEmpty()) {
-                    sb.append(Messages.format("%nFound these map keys without a corresponding value:%n"));
+                    sb.append(Errors.format("%nFound these map keys without a corresponding value:%n"));
                     for (Key<V> key : keysOnlyFromProviderMapEntrys) {
                         sb.append(
-                                Messages.format(
+                                Errors.format(
                                         "  '%s' bound at: %s%n",
                                         valueKeyToKey.get(key), valueKeyToEntryBinding.get(key).getSource()));
                     }
@@ -1314,8 +1354,8 @@ public final class RealMapBinder<K, V> implements Module {
             ProviderInstanceBinding<Map<K, V>> providerInstanceBinding =
                     (ProviderInstanceBinding<Map<K, V>>) mapBinding;
             @SuppressWarnings("unchecked")
-            RealMapProvider<K, V> mapProvider =
+            ExtensionRealMapProvider<K, V> mapProvider =
-                    (RealMapProvider<K, V>) providerInstanceBinding.getUserSuppliedProvider();
+                    (ExtensionRealMapProvider<K, V>) providerInstanceBinding.getUserSuppliedProvider();
 
             this.bindingSelection = mapProvider.getBindingSelection();
 
@@ -1346,7 +1386,9 @@ public final class RealMapBinder<K, V> implements Module {
     private static <K, V> InternalProvisionException createNullValueException(
             K key, Binding<V> binding) {
         return InternalProvisionException.create(
+                ErrorId.NULL_VALUE_IN_MAP,
                 "Map injection failed due to null value for key \"%s\", bound at: %s",
-                key, binding.getSource());
+                key,
+                binding.getSource());
     }
 }

src/main/java/com/google/inject/internal/RealMultibinder.java

@@ -5,7 +5,6 @@ import static com.google.inject.internal.Errors.checkConfiguration;
 import static com.google.inject.internal.Errors.checkNotNull;
 import static com.google.inject.name.Names.named;
 
-import com.google.common.base.Objects;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
@@ -24,6 +23,7 @@ import com.google.inject.multibindings.MultibinderBinding;
 import com.google.inject.multibindings.MultibindingsTargetVisitor;
 import com.google.inject.spi.BindingTargetVisitor;
 import com.google.inject.spi.Dependency;
+import com.google.inject.spi.Message;
 import com.google.inject.spi.ProviderInstanceBinding;
 import com.google.inject.spi.ProviderWithExtensionVisitor;
 import com.google.inject.util.Types;
@@ -31,6 +31,7 @@ import java.lang.reflect.Type;
 import java.util.Collection;
 import java.util.List;
 import java.util.Set;
+import java.util.function.Function;
 
 /**
  * The actual multibinder plays several roles:
@@ -81,6 +82,13 @@ public final class RealMultibinder<T> implements Module {
         return (TypeLiteral<Collection<javax.inject.Provider<T>>>) TypeLiteral.get(type);
     }
 
+    @SuppressWarnings("unchecked")
+    static <T> TypeLiteral<Set<? extends T>> setOfExtendsOf(TypeLiteral<T> elementType) {
+        Type extendsType = Types.subtypeOf(elementType.getType());
+        Type setOfExtendsType = Types.setOf(extendsType);
+        return (TypeLiteral<Set<? extends T>>) TypeLiteral.get(setOfExtendsType);
+    }
+
     private final BindingSelection<T> bindingSelection;
     private final Binder binder;
 
@@ -92,9 +100,17 @@ public final class RealMultibinder<T> implements Module {
     @Override
     public void configure(Binder binder) {
         checkConfiguration(!bindingSelection.isInitialized(), "Multibinder was already initialized");
+
+        RealMultibinderProvider<T> setProvider = new RealMultibinderProvider<T>(bindingSelection);
+        // Bind the setKey to the provider wrapped w/ extension support.
         binder
                 .bind(bindingSelection.getSetKey())
-                .toProvider(new RealMultibinderProvider<T>(bindingSelection));
+                .toProvider(new ExtensionRealMultibinderProvider<>(setProvider));
+        // Bind the <? extends T> to the provider w/o extension support.
+        // It's important the exactly one binding implement the extension support and show
+        // the other keys as aliases, to adhere to the extension contract.
+        binder.bind(bindingSelection.getSetOfExtendsKey()).toProvider(setProvider);
+
         Provider<Collection<Provider<T>>> collectionOfProvidersProvider =
                 new RealMultibinderCollectionOfProvidersProvider<T>(bindingSelection);
         binder
@@ -148,15 +164,19 @@ public final class RealMultibinder<T> implements Module {
         return bindingSelection.containsElement(element);
     }
 
-    private static final class RealMultibinderProvider<T>
+    /**
-            extends InternalProviderInstanceBindingImpl.Factory<Set<T>>
+     * Base implement of {@link InternalProviderInstanceBindingImpl.Factory} that works based on a
-            implements ProviderWithExtensionVisitor<Set<T>>, MultibinderBinding<Set<T>> {
+     * {@link BindingSelection}, allowing provider instances for various bindings to be implemented
-        private final BindingSelection<T> bindingSelection;
+     * with less duplication.
-        private List<Binding<T>> bindings;
+     */
-        private SingleParameterInjector<T>[] injectors;
+    private abstract static class BaseFactory<ValueT, ProvidedT>
-        private boolean permitDuplicates;
+            extends InternalProviderInstanceBindingImpl.Factory<ProvidedT> {
+        final Function<BindingSelection<ValueT>, ImmutableSet<Dependency<?>>> dependenciesFn;
+        final BindingSelection<ValueT> bindingSelection;
 
-        RealMultibinderProvider(BindingSelection<T> bindingSelection) {
+        BaseFactory(
+                BindingSelection<ValueT> bindingSelection,
+                Function<BindingSelection<ValueT>, ImmutableSet<Dependency<?>>> dependenciesFn) {
             // While Multibinders only depend on bindings created in modules so we could theoretically
             // initialize eagerly, they also depend on
             // 1. findBindingsByType returning results
@@ -164,23 +184,58 @@ public final class RealMultibinder<T> implements Module {
             // neither of those is available during eager initialization, so we use DELAYED
             super(InitializationTiming.DELAYED);
             this.bindingSelection = bindingSelection;
-        }
+            this.dependenciesFn = dependenciesFn;
-
-        @Override
-        public Set<Dependency<?>> getDependencies() {
-            return bindingSelection.getDependencies();
         }
 
         @Override
         void initialize(InjectorImpl injector, Errors errors) throws ErrorsException {
             bindingSelection.initialize(injector, errors);
-            this.bindings = bindingSelection.getBindings();
+            doInitialize();
-            this.injectors = bindingSelection.getParameterInjectors();
+        }
-            this.permitDuplicates = bindingSelection.permitsDuplicates();
+
+        abstract void doInitialize();
+
+        @Override
+        public Set<Dependency<?>> getDependencies() {
+            return dependenciesFn.apply(bindingSelection);
         }
 
         @Override
-        protected Set<T> doProvision(InternalContext context, Dependency<?> dependency)
+        public boolean equals(Object obj) {
+            return getClass().isInstance(obj)
+                    && bindingSelection.equals(((BaseFactory<?, ?>) obj).bindingSelection);
+        }
+
+        @Override
+        public int hashCode() {
+            return bindingSelection.hashCode();
+        }
+    }
+
+    /**
+     * Provider instance implementation that provides the actual set of values. This is parameterized
+     * so it can be used to supply a Set<T> and Set<? extends T>, the latter being useful for Kotlin
+     * support.
+     */
+    private static final class RealMultibinderProvider<T> extends BaseFactory<T, Set<T>> {
+        List<Binding<T>> bindings;
+        SingleParameterInjector<T>[] injectors;
+        boolean permitDuplicates;
+
+        RealMultibinderProvider(BindingSelection<T> bindingSelection) {
+            // Note: method reference doesn't work for the 2nd arg for some reason when compiling on java8
+            super(bindingSelection, bs -> bs.getDependencies());
+        }
+
+        @Override
+        protected void doInitialize() {
+            bindings = bindingSelection.getBindings();
+            injectors = bindingSelection.getParameterInjectors();
+            permitDuplicates = bindingSelection.permitsDuplicates();
+        }
+
+        @Override
+        protected ImmutableSet<T> doProvision(InternalContext context, Dependency<?> dependency)
                 throws InternalProvisionException {
             SingleParameterInjector<T>[] localInjectors = injectors;
             if (localInjectors == null) {
@@ -204,14 +259,52 @@ public final class RealMultibinder<T> implements Module {
             ImmutableSet<T> set = ImmutableSet.copyOf(values);
             // There are fewer items in the set than the array.  Figure out which one got dropped.
             if (!permitDuplicates && set.size() < values.length) {
-                throw newDuplicateValuesException(set, values);
+                throw newDuplicateValuesException(values);
             }
             return set;
         }
 
         private InternalProvisionException newNullEntryException(int i) {
             return InternalProvisionException.create(
-                    "Set injection failed due to null element bound at: %s", bindings.get(i).getSource());
+                    ErrorId.NULL_ELEMENT_IN_SET,
+                    "Set injection failed due to null element bound at: %s",
+                    bindings.get(i).getSource());
+        }
+
+        private InternalProvisionException newDuplicateValuesException(T[] values) {
+            Message message =
+                    new Message(
+                            GuiceInternal.GUICE_INTERNAL,
+                            ErrorId.DUPLICATE_ELEMENT,
+                            new DuplicateElementError<T>(
+                                    bindingSelection.getSetKey(), bindings, values, ImmutableList.of(getSource())));
+            return new InternalProvisionException(message);
+        }
+    }
+
+    /**
+     * Implementation of BaseFactory that exposes details about the multibinder through the extension
+     * SPI.
+     */
+    private static final class ExtensionRealMultibinderProvider<T> extends BaseFactory<T, Set<T>>
+            implements ProviderWithExtensionVisitor<Set<T>>, MultibinderBinding<Set<T>> {
+        final RealMultibinderProvider<T> delegate;
+
+        ExtensionRealMultibinderProvider(RealMultibinderProvider<T> delegate) {
+            // Note: method reference doesn't work for the 2nd arg for some reason when compiling on java8
+            super(delegate.bindingSelection, bs -> bs.getDependencies());
+            this.delegate = delegate;
+        }
+
+        @Override
+        protected void doInitialize() {
+            delegate.doInitialize();
+        }
+
+        @Override
+        protected ImmutableSet<T> doProvision(InternalContext context, Dependency<?> dependency)
+                throws InternalProvisionException {
+            return delegate.doProvision(context, dependency);
         }
 
         @SuppressWarnings("unchecked")
@@ -225,69 +318,17 @@ public final class RealMultibinder<T> implements Module {
             }
         }
 
-        private InternalProvisionException newDuplicateValuesException(
-                ImmutableSet<T> set, T[] values) {
-            // TODO(lukes): consider reporting all duplicate values, the easiest way would be to rebuild
-            // a new set and detect dupes as we go
-            // Find the duplicate binding
-            // To do this we take advantage of the fact that set, values and bindings all have the same
-            // ordering for a non-empty prefix of the set.
-            // First we scan for the first item dropped from the set.
-            int newBindingIndex = 0;
-            for (T item : set) {
-                if (item != values[newBindingIndex]) {
-                    break;
-                }
-                newBindingIndex++;
-            }
-            // once we exit the loop newBindingIndex will point at the first item in values that was
-            // dropped.
-
-            Binding<T> newBinding = bindings.get(newBindingIndex);
-            T newValue = values[newBindingIndex];
-            // Now we scan again to find the index of the value, we are guaranteed to find it.
-            int oldBindingIndex = set.asList().indexOf(newValue);
-            T oldValue = values[oldBindingIndex];
-            Binding<T> duplicateBinding = bindings.get(oldBindingIndex);
-            String oldString = oldValue.toString();
-            String newString = newValue.toString();
-            if (Objects.equal(oldString, newString)) {
-                // When the value strings match, just show the source of the bindings
-                return InternalProvisionException.create(
-                        "Set injection failed due to duplicated element \"%s\""
-                                + "\n    Bound at %s\n    Bound at %s",
-                        newValue, duplicateBinding.getSource(), newBinding.getSource());
-            } else {
-                // When the value strings don't match, include them both as they may be useful for debugging
-                return InternalProvisionException.create(
-                        "Set injection failed due to multiple elements comparing equal:"
-                                + "\n    \"%s\"\n        bound at %s"
-                                + "\n    \"%s\"\n        bound at %s",
-                        oldValue, duplicateBinding.getSource(), newValue, newBinding.getSource());
-            }
-        }
-
-        @Override
-        public boolean equals(Object obj) {
-            return obj instanceof RealMultibinderProvider
-                    && bindingSelection.equals(((RealMultibinderProvider<?>) obj).bindingSelection);
-        }
-
-        @Override
-        public int hashCode() {
-            return bindingSelection.hashCode();
-        }
-
         @Override
         public Key<Set<T>> getSetKey() {
             return bindingSelection.getSetKey();
         }
 
         @Override
-        public Set<Key<?>> getAlternateSetKeys() {
+        public ImmutableSet<Key<?>> getAlternateSetKeys() {
             return ImmutableSet.of(
                     (Key<?>) bindingSelection.getCollectionOfProvidersKey(),
-                    (Key<?>) bindingSelection.getCollectionOfJavaxProvidersKey());
+                    (Key<?>) bindingSelection.getCollectionOfJavaxProvidersKey(),
+                    (Key<?>) bindingSelection.getSetOfExtendsKey());
         }
 
         @Override
@@ -311,6 +352,34 @@ public final class RealMultibinder<T> implements Module {
         }
     }
 
+    /**
+     * Implementation of BaseFactory that exposes a collection of providers of the values in the set.
+     */
+    private static final class RealMultibinderCollectionOfProvidersProvider<T>
+            extends BaseFactory<T, Collection<Provider<T>>> {
+        ImmutableList<Provider<T>> providers;
+
+        RealMultibinderCollectionOfProvidersProvider(BindingSelection<T> bindingSelection) {
+            // Note: method reference doesn't work for the 2nd arg for some reason when compiling on java8
+            super(bindingSelection, bs -> bs.getProviderDependencies());
+        }
+
+        @Override
+        protected void doInitialize() {
+            ImmutableList.Builder<Provider<T>> providers = ImmutableList.builder();
+            for (Binding<T> binding : bindingSelection.getBindings()) {
+                providers.add(binding.getProvider());
+            }
+            this.providers = providers.build();
+        }
+
+        @Override
+        protected ImmutableList<Provider<T>> doProvision(
+                InternalContext context, Dependency<?> dependency) {
+            return providers;
+        }
+    }
+
     private static final class BindingSelection<T> {
         // prior to initialization we declare just a dependency on the injector, but as soon as we are
         // initialized we swap to dependencies on the elements.
@@ -323,6 +392,7 @@ public final class RealMultibinder<T> implements Module {
         private String setName;
         private Key<Collection<Provider<T>>> collectionOfProvidersKey;
         private Key<Collection<javax.inject.Provider<T>>> collectionOfJavaxProvidersKey;
+        private Key<Set<? extends T>> setOfExtendsKey;
         private Key<Boolean> permitDuplicatesKey;
 
         private boolean isInitialized;
@@ -448,6 +518,14 @@ public final class RealMultibinder<T> implements Module {
             return local;
         }
 
+        Key<Set<? extends T>> getSetOfExtendsKey() {
+            Key<Set<? extends T>> local = setOfExtendsKey;
+            if (local == null) {
+                local = setOfExtendsKey = setKey.ofType(setOfExtendsOf(elementType));
+            }
+            return local;
+        }
+
         boolean isInitialized() {
             return isInitialized;
         }
@@ -487,7 +565,8 @@ public final class RealMultibinder<T> implements Module {
                         || binding.getKey().equals(getPermitDuplicatesKey())
                         || binding.getKey().equals(setKey)
                         || binding.getKey().equals(collectionOfProvidersKey)
-                        || binding.getKey().equals(collectionOfJavaxProvidersKey);
+                        || binding.getKey().equals(collectionOfJavaxProvidersKey)
+                        || binding.getKey().equals(setOfExtendsKey);
             } else {
                 return false;
             }
@@ -533,51 +612,6 @@ public final class RealMultibinder<T> implements Module {
         return bindingSelection.hashCode();
     }
 
-    private static final class RealMultibinderCollectionOfProvidersProvider<T>
-            extends InternalProviderInstanceBindingImpl.Factory<Collection<Provider<T>>> {
-
-        private final BindingSelection<T> bindingSelection;
-        private ImmutableList<Provider<T>> collectionOfProviders;
-
-        RealMultibinderCollectionOfProvidersProvider(BindingSelection<T> bindingSelection) {
-            super(InitializationTiming.DELAYED); // See comment in RealMultibinderProvider
-            this.bindingSelection = bindingSelection;
-        }
-
-        @Override
-        void initialize(InjectorImpl injector, Errors errors) throws ErrorsException {
-            bindingSelection.initialize(injector, errors);
-            ImmutableList.Builder<Provider<T>> providers = ImmutableList.builder();
-            for (Binding<T> binding : bindingSelection.getBindings()) {
-                providers.add(binding.getProvider());
-            }
-            this.collectionOfProviders = providers.build();
-        }
-
-        @Override
-        protected Collection<Provider<T>> doProvision(
-                InternalContext context, Dependency<?> dependency) {
-            return collectionOfProviders;
-        }
-
-        @Override
-        public Set<Dependency<?>> getDependencies() {
-            return bindingSelection.getProviderDependencies();
-        }
-
-        @Override
-        public boolean equals(Object obj) {
-            return obj instanceof RealMultibinderCollectionOfProvidersProvider
-                    && bindingSelection.equals(
-                    ((RealMultibinderCollectionOfProvidersProvider<?>) obj).bindingSelection);
-        }
-
-        @Override
-        public int hashCode() {
-            return bindingSelection.hashCode();
-        }
-    }
-
     /**
      * We install the permit duplicates configuration as its own binding, all by itself. This way, if
      * only one of a multibinder's users remember to call permitDuplicates(), they're still permitted.

src/main/java/com/google/inject/internal/ScopeBindingProcessor.java

@@ -1,12 +1,11 @@
 package com.google.inject.internal;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+
 import com.google.inject.Scope;
 import com.google.inject.spi.ScopeBinding;
-
 import java.lang.annotation.Annotation;
 
-import static com.google.common.base.Preconditions.checkNotNull;
-
 /**
  * Handles {@code Binder.bindScope} commands.
  *
@@ -20,7 +19,8 @@ final class ScopeBindingProcessor extends AbstractProcessor {
     @Override
     public Boolean visit(ScopeBinding command) {
         Scope scope = checkNotNull(command.getScope(), "scope");
-        Class<? extends Annotation> annotationType = checkNotNull(command.getAnnotationType(), "annotation type");
+        Class<? extends Annotation> annotationType =
+                checkNotNull(command.getAnnotationType(), "annotation type");
 
         if (!Annotations.isScopeAnnotation(annotationType)) {
             errors.missingScopeAnnotation(annotationType);
@@ -32,13 +32,13 @@ final class ScopeBindingProcessor extends AbstractProcessor {
             // Go ahead and bind anyway so we don't get collateral errors.
         }
 
-        ScopeBinding existing = injector.state.getScopeBinding(annotationType);
+        ScopeBinding existing = injector.getBindingData().getScopeBinding(annotationType);
         if (existing != null) {
             if (!scope.equals(existing.getScope())) {
                 errors.duplicateScopes(existing, annotationType, scope);
             }
         } else {
-            injector.state.putScopeBinding(annotationType, command);
+            injector.getBindingData().putScopeBinding(annotationType, command);
         }
 
         return true;

src/main/java/com/google/inject/internal/ScopeNotFoundError.java

@@ -0,0 +1,47 @@
+package com.google.inject.internal;
+
+import com.google.common.collect.Lists;
+import com.google.inject.spi.ErrorDetail;
+import java.lang.annotation.Annotation;
+import java.util.ArrayList;
+import java.util.Formatter;
+import java.util.List;
+
+/** Error reported by Guice when a scope annotation is not bound to any scope implementation. */
+final class ScopeNotFoundError extends InternalErrorDetail<ScopeNotFoundError> {
+
+    private final Class<? extends Annotation> scopeAnnotation;
+
+    ScopeNotFoundError(Class<? extends Annotation> scopeAnnotation, List<Object> sources) {
+        super(
+                ErrorId.SCOPE_NOT_FOUND,
+                String.format("No scope is bound to %s.", Messages.convert(scopeAnnotation)),
+                sources,
+                null);
+        this.scopeAnnotation = scopeAnnotation;
+    }
+
+    @Override
+    public boolean isMergeable(ErrorDetail<?> other) {
+        return other instanceof ScopeNotFoundError
+                && ((ScopeNotFoundError) other).scopeAnnotation.equals(scopeAnnotation);
+    }
+
+    @Override
+    protected void formatDetail(List<ErrorDetail<?>> mergeableErrors, Formatter formatter) {
+        List<List<Object>> sourcesSet = new ArrayList<>();
+        sourcesSet.add(getSources());
+        mergeableErrors.stream().map(ErrorDetail::getSources).forEach(sourcesSet::add);
+
+        formatter.format("%n%s%n", "Used at:");
+        int sourceListIndex = 1;
+        for (List<Object> sources : sourcesSet) {
+            ErrorFormatter.formatSources(sourceListIndex++, Lists.reverse(sources), formatter);
+        }
+    }
+
+    @Override
+    public ScopeNotFoundError withSources(List<Object> newSources) {
+        return new ScopeNotFoundError(scopeAnnotation, newSources);
+    }
+}

src/main/java/com/google/inject/internal/Scoping.java

@@ -10,7 +10,6 @@ import com.google.inject.Stage;
 import com.google.inject.binder.ScopedBindingBuilder;
 import com.google.inject.spi.BindingScopingVisitor;
 import com.google.inject.spi.ScopeBinding;
-
 import java.lang.annotation.Annotation;
 
 /**
@@ -24,7 +23,8 @@ public abstract class Scoping {
      * No scoping annotation has been applied. Note that this is different from {@code
      * in(Scopes.NO_SCOPE)}, where the 'NO_SCOPE' has been explicitly applied.
      */
-    public static final Scoping UNSCOPED = new Scoping() {
+    public static final Scoping UNSCOPED =
+            new Scoping() {
                 @Override
                 public <V> V acceptVisitor(BindingScopingVisitor<V> visitor) {
                     return visitor.visitNoScoping();
@@ -46,7 +46,35 @@ public abstract class Scoping {
                 }
             };
 
-    public static final Scoping SINGLETON_ANNOTATION = new Scoping() {
+    /**
+     * No scoping annotation has been applied explicitly. Note that this is is the same as {@code
+     * in(Scopes.NO_SCOPE)}.
+     */
+    private static final Scoping EXPLICITLY_UNSCOPED =
+            new Scoping() {
+                @Override
+                public <V> V acceptVisitor(BindingScopingVisitor<V> visitor) {
+                    return visitor.visitNoScoping();
+                }
+
+                @Override
+                public Scope getScopeInstance() {
+                    return Scopes.NO_SCOPE;
+                }
+
+                @Override
+                public String toString() {
+                    return Scopes.NO_SCOPE.toString();
+                }
+
+                @Override
+                public void applyTo(ScopedBindingBuilder scopedBindingBuilder) {
+                    scopedBindingBuilder.in(Scopes.NO_SCOPE);
+                }
+            };
+
+    public static final Scoping SINGLETON_ANNOTATION =
+            new Scoping() {
                 @Override
                 public <V> V acceptVisitor(BindingScopingVisitor<V> visitor) {
                     return visitor.visitScopeAnnotation(Singleton.class);
@@ -68,7 +96,8 @@ public abstract class Scoping {
                 }
             };
 
-    public static final Scoping SINGLETON_INSTANCE = new Scoping() {
+    public static final Scoping SINGLETON_INSTANCE =
+            new Scoping() {
                 @Override
                 public <V> V acceptVisitor(BindingScopingVisitor<V> visitor) {
                     return visitor.visitScope(Scopes.SINGLETON);
@@ -90,7 +119,8 @@ public abstract class Scoping {
                 }
             };
 
-    public static final Scoping EAGER_SINGLETON = new Scoping() {
+    public static final Scoping EAGER_SINGLETON =
+            new Scoping() {
                 @Override
                 public <V> V acceptVisitor(BindingScopingVisitor<V> visitor) {
                     return visitor.visitEagerSingleton();
@@ -112,12 +142,8 @@ public abstract class Scoping {
                 }
             };
 
-    private Scoping() {
-    }
-
     public static Scoping forAnnotation(final Class<? extends Annotation> scopingAnnotation) {
-        if (scopingAnnotation == Singleton.class
+        if (scopingAnnotation == Singleton.class || scopingAnnotation == javax.inject.Singleton.class) {
-                || scopingAnnotation == javax.inject.Singleton.class) {
             return SINGLETON_ANNOTATION;
         }
 
@@ -147,6 +173,8 @@ public abstract class Scoping {
     public static Scoping forInstance(final Scope scope) {
         if (scope == Scopes.SINGLETON) {
             return SINGLETON_INSTANCE;
+        } else if (scope == Scopes.NO_SCOPE) {
+            return EXPLICITLY_UNSCOPED;
         }
 
         return new Scoping() {
@@ -172,42 +200,6 @@ public abstract class Scoping {
         };
     }
 
-    /**
-     * Scopes an internal factory.
-     */
-    static <T> InternalFactory<? extends T> scope(Key<T> key, InjectorImpl injector,
-                                                  InternalFactory<? extends T> creator, Object source, Scoping scoping) {
-
-        if (scoping.isNoScope()) {
-            return creator;
-        }
-
-        Scope scope = scoping.getScopeInstance();
-
-        Provider<T> scoped = scope.scope(key, new ProviderToInternalFactoryAdapter<T>(injector, creator));
-        return new InternalFactoryToProviderAdapter<T>(scoped, source);
-    }
-
-    /**
-     * Replaces annotation scopes with instance scopes using the Injector's annotation-to-instance
-     * map. If the scope annotation has no corresponding instance, an error will be added and unscoped
-     * will be retuned.
-     */
-    static Scoping makeInjectable(Scoping scoping, InjectorImpl injector, Errors errors) {
-        Class<? extends Annotation> scopeAnnotation = scoping.getScopeAnnotation();
-        if (scopeAnnotation == null) {
-            return scoping;
-        }
-
-        ScopeBinding scope = injector.state.getScopeBinding(scopeAnnotation);
-        if (scope != null) {
-            return forInstance(scope.getScope());
-        }
-
-        errors.scopeNotFound(scopeAnnotation);
-        return UNSCOPED;
-    }
-
     /**
      * Returns true if this scope was explicitly applied. If no scope was explicitly applied then the
      * scoping annotation will be used.
@@ -224,28 +216,25 @@ public abstract class Scoping {
         return getScopeInstance() == Scopes.NO_SCOPE;
     }
 
-    /**
+    /** Returns true if this scope is a singleton that should be loaded eagerly in {@code stage}. */
-     * Returns true if this scope is a singleton that should be loaded eagerly in {@code stage}.
-     */
     public boolean isEagerSingleton(Stage stage) {
         if (this == EAGER_SINGLETON) {
             return true;
         }
 
-        return stage == Stage.PRODUCTION && (this == SINGLETON_ANNOTATION || this == SINGLETON_INSTANCE);
+        if (stage == Stage.PRODUCTION) {
-
+            return this == SINGLETON_ANNOTATION || this == SINGLETON_INSTANCE;
         }
 
-    /**
+        return false;
-     * Returns the scope instance, or {@code null} if that isn't known for this instance.
+    }
-     */
+
+    /** Returns the scope instance, or {@code null} if that isn't known for this instance. */
     public Scope getScopeInstance() {
         return null;
     }
 
-    /**
+    /** Returns the scope annotation, or {@code null} if that isn't known for this instance. */
-     * Returns the scope annotation, or {@code null} if that isn't known for this instance.
-     */
     public Class<? extends Annotation> getScopeAnnotation() {
         return null;
     }
@@ -269,4 +258,48 @@ public abstract class Scoping {
     public abstract <V> V acceptVisitor(BindingScopingVisitor<V> visitor);
 
     public abstract void applyTo(ScopedBindingBuilder scopedBindingBuilder);
+
+    private Scoping() {}
+
+    /** Scopes an internal factory. */
+    static <T> InternalFactory<? extends T> scope(
+            Key<T> key,
+            InjectorImpl injector,
+            InternalFactory<? extends T> creator,
+            Object source,
+            Scoping scoping) {
+
+        if (scoping.isNoScope()) {
+            return creator;
+        }
+
+        Scope scope = scoping.getScopeInstance();
+
+        // NOTE: SingletonScope relies on the fact that we are passing a
+        // ProviderToInternalFactoryAdapter here.  If you change the type make sure to update
+        // SingletonScope as well.
+        Provider<T> scoped =
+                scope.scope(key, new ProviderToInternalFactoryAdapter<T>(injector, creator));
+        return new InternalFactoryToProviderAdapter<T>(scoped, source);
+    }
+
+    /**
+     * Replaces annotation scopes with instance scopes using the Injector's annotation-to-instance
+     * map. If the scope annotation has no corresponding instance, an error will be added and unscoped
+     * will be retuned.
+     */
+    static Scoping makeInjectable(Scoping scoping, InjectorImpl injector, Errors errors) {
+        Class<? extends Annotation> scopeAnnotation = scoping.getScopeAnnotation();
+        if (scopeAnnotation == null) {
+            return scoping;
+        }
+
+        ScopeBinding scope = injector.getBindingData().getScopeBinding(scopeAnnotation);
+        if (scope != null) {
+            return forInstance(scope.getScope());
+        }
+
+        errors.scopeNotFound(scopeAnnotation);
+        return UNSCOPED;
+    }
 }

src/main/java/com/google/inject/internal/SourceFormatter.java

@@ -0,0 +1,169 @@
+package com.google.inject.internal;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import com.google.common.base.Strings;
+import com.google.common.collect.Lists;
+import com.google.inject.Key;
+import com.google.inject.TypeLiteral;
+import com.google.inject.internal.util.Classes;
+import com.google.inject.internal.util.StackTraceElements;
+import com.google.inject.spi.Dependency;
+import com.google.inject.spi.ElementSource;
+import com.google.inject.spi.InjectionPoint;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.lang.reflect.Member;
+import java.lang.reflect.Method;
+import java.lang.reflect.Parameter;
+import java.util.Formatter;
+import java.util.List;
+
+/** Formatting a single source in Guice error message. */
+final class SourceFormatter {
+    static final String INDENT = Strings.repeat(" ", 5);
+
+    private final Object source;
+    private final Formatter formatter;
+    private final boolean omitPreposition;
+    private final String moduleStack;
+
+    SourceFormatter(Object source, Formatter formatter, boolean omitPreposition) {
+        if (source instanceof ElementSource) {
+            ElementSource elementSource = (ElementSource) source;
+            this.source = elementSource.getDeclaringSource();
+            this.moduleStack = getModuleStack(elementSource);
+        } else {
+            this.source = source;
+            this.moduleStack = "";
+        }
+        this.formatter = formatter;
+        this.omitPreposition = omitPreposition;
+    }
+
+    void format() {
+        boolean appendModuleSource = !moduleStack.isEmpty();
+        if (source instanceof Dependency) {
+            formatDependency((Dependency<?>) source);
+        } else if (source instanceof InjectionPoint) {
+            formatInjectionPoint(null, (InjectionPoint) source);
+        } else if (source instanceof Class) {
+            formatter.format("%s%s%n", preposition("at "), StackTraceElements.forType((Class<?>) source));
+        } else if (source instanceof Member) {
+            formatMember((Member) source);
+        } else if (source instanceof TypeLiteral) {
+            formatter.format("%s%s%n", preposition("while locating "), source);
+        } else if (source instanceof Key) {
+            formatKey((Key<?>) source);
+        } else if (source instanceof Thread) {
+            appendModuleSource = false;
+            formatter.format("%s%s%n", preposition("in thread "), source);
+        } else {
+            formatter.format("%s%s%n", preposition("at "), source);
+        }
+
+        if (appendModuleSource) {
+            formatter.format("%s \\_ installed by: %s%n", INDENT, moduleStack);
+        }
+    }
+
+    private String preposition(String prepostition) {
+        if (omitPreposition) {
+            return "";
+        }
+        return prepostition;
+    }
+
+    private void formatDependency(Dependency<?> dependency) {
+        InjectionPoint injectionPoint = dependency.getInjectionPoint();
+        if (injectionPoint != null) {
+            formatInjectionPoint(dependency, injectionPoint);
+        } else {
+            formatKey(dependency.getKey());
+        }
+    }
+
+    private void formatKey(Key<?> key) {
+        formatter.format("%s%s%n", preposition("while locating "), Messages.convert(key));
+    }
+
+    private void formatMember(Member member) {
+        formatter.format("%s%s%n", preposition("at "), StackTraceElements.forMember(member));
+    }
+
+    private void formatInjectionPoint(Dependency<?> dependency, InjectionPoint injectionPoint) {
+        Member member = injectionPoint.getMember();
+        Class<? extends Member> memberType = Classes.memberType(member);
+        formatMember(injectionPoint.getMember());
+        if (memberType == Field.class) {
+            formatter.format("%s \\_ for field %s%n", INDENT, Messages.redBold(member.getName()));
+        } else if (dependency != null) {
+
+            formatter.format("%s \\_ for %s%n", INDENT, getParameterName(dependency));
+        }
+    }
+
+    static String getModuleStack(ElementSource elementSource) {
+        if (elementSource == null) {
+            return "";
+        }
+        List<String> modules = Lists.newArrayList(elementSource.getModuleClassNames());
+        // Insert any original element sources w/ module info into the path.
+        while (elementSource.getOriginalElementSource() != null) {
+            elementSource = elementSource.getOriginalElementSource();
+            modules.addAll(0, elementSource.getModuleClassNames());
+        }
+        if (modules.size() <= 1) {
+            return "";
+        }
+        return String.join(" -> ", Lists.reverse(modules));
+    }
+
+    static String getParameterName(Dependency<?> dependency) {
+        int parameterIndex = dependency.getParameterIndex();
+        int ordinal = parameterIndex + 1;
+        Member member = dependency.getInjectionPoint().getMember();
+        Parameter parameter = null;
+        if (member instanceof Constructor) {
+            parameter = ((Constructor<?>) member).getParameters()[parameterIndex];
+        } else if (member instanceof Method) {
+            parameter = ((Method) member).getParameters()[parameterIndex];
+        }
+        String parameterName = "";
+        if (parameter != null && parameter.isNamePresent()) {
+            parameterName = parameter.getName();
+        }
+        return String.format(
+                "%s%s parameter%s",
+                ordinal,
+                getOrdinalSuffix(ordinal),
+                parameterName.isEmpty() ? "" : " " + Messages.redBold(parameterName));
+    }
+
+    /**
+     * Maps {@code 1} to the string {@code "1st"} ditto for all non-negative numbers
+     *
+     * @see <a href="https://en.wikipedia.org/wiki/English_numerals#Ordinal_numbers">
+     *     https://en.wikipedia.org/wiki/English_numerals#Ordinal_numbers</a>
+     */
+    private static String getOrdinalSuffix(int ordinal) {
+        // negative ordinals don't make sense, we allow zero though because we are programmers
+        checkArgument(ordinal >= 0);
+        if ((ordinal / 10) % 10 == 1) {
+            // all the 'teens' are weird
+            return "th";
+        } else {
+            // could use a lookup table? any better?
+            switch (ordinal % 10) {
+                case 1:
+                    return "st";
+                case 2:
+                    return "nd";
+                case 3:
+                    return "rd";
+                default:
+                    return "th";
+            }
+        }
+    }
+}

src/main/java/com/google/inject/internal/TypeConverterBindingProcessor.java

@@ -7,7 +7,6 @@ import com.google.inject.matcher.Matcher;
 import com.google.inject.matcher.Matchers;
 import com.google.inject.spi.TypeConverter;
 import com.google.inject.spi.TypeConverterBinding;
-
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Type;
@@ -22,9 +21,7 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
         super(errors);
     }
 
-    /**
+    /** Installs default converters for primitives, enums, and class literals. */
-     * Installs default converters for primitives, enums, and class literals.
-     */
     static void prepareBuiltInConverters(InjectorImpl injector) {
         // Configure type converters.
         convertToPrimitiveType(injector, int.class, Integer.class);
@@ -35,7 +32,11 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
         convertToPrimitiveType(injector, float.class, Float.class);
         convertToPrimitiveType(injector, double.class, Double.class);
 
-        convertToClass(injector, Character.class, new TypeConverter() {
+        convertToClass(
+                injector,
+                Character.class,
+                new TypeConverter() {
+                    @Override
                     public Object convert(String value, TypeLiteral<?> toType) {
                         value = value.trim();
                         if (value.length() != 1) {
@@ -50,8 +51,12 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
                     }
                 });
 
-        convertToClasses(injector, Matchers.subclassesOf(Enum.class), new TypeConverter() {
+        convertToClasses(
-            @SuppressWarnings("unchecked")
+                injector,
+                Matchers.subclassesOf(Enum.class),
+                new TypeConverter() {
+                    @SuppressWarnings("rawtypes") // Unavoidable, only way to use Enum.valueOf
+                    @Override
                     public Object convert(String value, TypeLiteral<?> toType) {
                         return Enum.valueOf((Class) toType.getRawType(), value);
                     }
@@ -62,7 +67,9 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
                     }
                 });
 
-        internalConvertToTypes(injector, new AbstractMatcher<>() {
+        internalConvertToTypes(
+                injector,
+                new AbstractMatcher<TypeLiteral<?>>() {
                     @Override
                     public boolean matches(TypeLiteral<?> typeLiteral) {
                         return typeLiteral.getRawType() == Class.class;
@@ -74,6 +81,7 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
                     }
                 },
                 new TypeConverter() {
+                    @Override
                     public Object convert(String value, TypeLiteral<?> toType) {
                         try {
                             return Class.forName(value);
@@ -86,17 +94,18 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
                     public String toString() {
                         return "TypeConverter<Class<?>>";
                     }
-                }
+                });
-        );
     }
 
-    private static <T> void convertToPrimitiveType(InjectorImpl injector, Class<T> primitiveType,
+    private static <T> void convertToPrimitiveType(
-                                                   final Class<T> wrapperType) {
+            InjectorImpl injector, Class<T> primitiveType, final Class<T> wrapperType) {
         try {
-            final Method parser = wrapperType.getMethod(
+            final Method parser =
-                    "parse" + capitalize(primitiveType.getName()), String.class);
+                    wrapperType.getMethod("parse" + capitalize(primitiveType.getName()), String.class);
 
-            TypeConverter typeConverter = new TypeConverter() {
+            TypeConverter typeConverter =
+                    new TypeConverter() {
+                        @Override
                         public Object convert(String value, TypeLiteral<?> toType) {
                             try {
                                 return parser.invoke(null, value);
@@ -119,14 +128,17 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
         }
     }
 
-    private static <T> void convertToClass(InjectorImpl injector, Class<T> type,
+    private static <T> void convertToClass(
-                                           TypeConverter converter) {
+            InjectorImpl injector, Class<T> type, TypeConverter converter) {
         convertToClasses(injector, Matchers.identicalTo(type), converter);
     }
 
-    private static void convertToClasses(InjectorImpl injector,
+    private static void convertToClasses(
-                                         final Matcher<? super Class<?>> typeMatcher, TypeConverter converter) {
+            InjectorImpl injector, final Matcher<? super Class<?>> typeMatcher, TypeConverter converter) {
-        internalConvertToTypes(injector, new AbstractMatcher<>() {
+        internalConvertToTypes(
+                injector,
+                new AbstractMatcher<TypeLiteral<?>>() {
+                    @Override
                     public boolean matches(TypeLiteral<?> typeLiteral) {
                         Type type = typeLiteral.getType();
                         if (!(type instanceof Class)) {
@@ -140,31 +152,34 @@ final class TypeConverterBindingProcessor extends AbstractProcessor {
                     public String toString() {
                         return typeMatcher.toString();
                     }
-        }, converter);
+                },
+                converter);
+    }
+
+    private static void internalConvertToTypes(
+            InjectorImpl injector, Matcher<? super TypeLiteral<?>> typeMatcher, TypeConverter converter) {
+        injector
+                .getBindingData()
+                .addConverter(
+                        new TypeConverterBinding(SourceProvider.UNKNOWN_SOURCE, typeMatcher, converter));
     }
 
     @Override
     public Boolean visit(TypeConverterBinding command) {
-        injector.state.addConverter(new TypeConverterBinding(
+        injector
+                .getBindingData()
+                .addConverter(
+                        new TypeConverterBinding(
                                 command.getSource(), command.getTypeMatcher(), command.getTypeConverter()));
         return true;
     }
 
-    private static void internalConvertToTypes(InjectorImpl injector,
-                                               Matcher<? super TypeLiteral<?>> typeMatcher,
-                                               TypeConverter converter) {
-        injector.state.addConverter(
-                new TypeConverterBinding(SourceProvider.UNKNOWN_SOURCE, typeMatcher, converter));
-    }
-
     private static String capitalize(String s) {
         if (s.length() == 0) {
             return s;
         }
         char first = s.charAt(0);
         char capitalized = Character.toUpperCase(first);
-        return (first == capitalized)
+        return (first == capitalized) ? s : capitalized + s.substring(1);
-                ? s
-                : capitalized + s.substring(1);
     }
 }

src/main/java/com/google/inject/internal/WeakKeySet.java

@@ -5,14 +5,13 @@ import com.google.common.base.Preconditions;
 import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.RemovalCause;
-import com.google.common.cache.RemovalListener;
+import com.google.common.cache.RemovalNotification;
 import com.google.common.collect.LinkedHashMultiset;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Multiset;
 import com.google.common.collect.Sets;
 import com.google.inject.Key;
 import com.google.inject.internal.util.SourceProvider;
-
 import java.util.Map;
 import java.util.Set;
 
@@ -21,38 +20,29 @@ import java.util.Set;
  */
 final class WeakKeySet {
 
+    private Map<Key<?>, Multiset<Object>> backingMap;
+
     /**
      * This is already locked externally on add and getSources but we need it to handle clean up in
      * the evictionCache's RemovalListener.
      */
     private final Object lock;
 
-    private Map<Key<?>, Multiset<Object>> backingMap;
     /**
-     * Tracks child injector lifetimes and evicts blacklisted keys/sources after the child injector is
+     * Tracks child injector lifetimes and evicts banned keys/sources after the child injector is
      * garbage collected.
      */
-    private final Cache<State, Set<KeyAndSource>> evictionCache = CacheBuilder.newBuilder()
+    private final Cache<InjectorBindingData, Set<KeyAndSource>> evictionCache =
-            .weakKeys()
+            CacheBuilder.newBuilder().weakKeys().removalListener(this::cleanupOnRemoval).build();
-            .removalListener(
+
-                    (RemovalListener<State, Set<KeyAndSource>>) notification -> {
+    private void cleanupOnRemoval(
+            RemovalNotification<InjectorBindingData, Set<KeyAndSource>> notification) {
         Preconditions.checkState(RemovalCause.COLLECTED.equals(notification.getCause()));
 
-                        cleanUpForCollectedState(notification.getValue());
+        // There may be multiple child injectors banning a certain key so only remove the source
-                    })
+        // that's relevant.
-            .build();
-
-    WeakKeySet(Object lock) {
-        this.lock = lock;
-    }
-
-    /**
-     * There may be multiple child injectors blacklisting a certain key so only remove the source
-     * that's relevant.
-     */
-    private void cleanUpForCollectedState(Set<KeyAndSource> keysAndSources) {
         synchronized (lock) {
-            for (KeyAndSource keyAndSource : keysAndSources) {
+            for (KeyAndSource keyAndSource : notification.getValue()) {
                 Multiset<Object> set = backingMap.get(keyAndSource.key);
                 if (set != null) {
                     set.remove(keyAndSource.source);
@@ -64,7 +54,11 @@ final class WeakKeySet {
         }
     }
 
-    public void add(Key<?> key, State state, Object source) {
+    WeakKeySet(Object lock) {
+        this.lock = lock;
+    }
+
+    public void add(Key<?> key, InjectorBindingData state, Object source) {
         if (backingMap == null) {
             backingMap = Maps.newHashMap();
         }
@@ -73,11 +67,11 @@ final class WeakKeySet {
         if (source instanceof Class || source == SourceProvider.UNKNOWN_SOURCE) {
             source = null;
         }
-        Object convertedSource = Messages.convert(source);
+        Object convertedSource = Errors.convert(source);
         backingMap.computeIfAbsent(key, k -> LinkedHashMultiset.create()).add(convertedSource);
 
         // Avoid all the extra work if we can.
-        if (state.parent() != State.NONE) {
+        if (state.parent().isPresent()) {
             Set<KeyAndSource> keyAndSources = evictionCache.getIfPresent(state);
             if (keyAndSources == null) {
                 evictionCache.put(state, keyAndSources = Sets.newHashSet());
@@ -122,8 +116,7 @@ final class WeakKeySet {
             }
 
             KeyAndSource other = (KeyAndSource) obj;
-            return Objects.equal(key, other.key)
+            return Objects.equal(key, other.key) && Objects.equal(source, other.source);
-                    && Objects.equal(source, other.source);
         }
     }
 }

src/main/java/com/google/inject/internal/util/ContinuousStopwatch.java

@@ -0,0 +1,37 @@
+package com.google.inject.internal.util;
+
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+
+import com.google.common.base.Stopwatch;
+import java.util.logging.Logger;
+
+/**
+ * A continuously timing stopwatch that is used for simple performance monitoring.
+ */
+public final class ContinuousStopwatch {
+    private final Logger logger = Logger.getLogger(ContinuousStopwatch.class.getName());
+    private final Stopwatch stopwatch;
+
+    /**
+     * Constructs a ContinuousStopwatch, which will start timing immediately after construction.
+     *
+     * @param stopwatch the internal stopwatch used by ContinuousStopwatch
+     */
+    public ContinuousStopwatch(Stopwatch stopwatch) {
+        this.stopwatch = stopwatch;
+        reset();
+    }
+
+    /** Resets and returns elapsed time in milliseconds. */
+    public long reset() {
+        long elapsedTimeMs = stopwatch.elapsed(MILLISECONDS);
+        stopwatch.reset();
+        stopwatch.start();
+        return elapsedTimeMs;
+    }
+
+    /** Resets and logs elapsed time in milliseconds. */
+    public void resetAndLog(String label) {
+        logger.fine(label + ": " + reset() + "ms");
+    }
+}

src/main/java/com/google/inject/spi/BindingSourceRestriction.java

@@ -0,0 +1,350 @@
+package com.google.inject.spi;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static java.util.stream.Collectors.toList;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Iterables;
+import com.google.inject.Binding;
+import com.google.inject.Key;
+import com.google.inject.RestrictedBindingSource;
+import com.google.inject.RestrictedBindingSource.RestrictionLevel;
+import com.google.inject.internal.Errors;
+import com.google.inject.internal.GuiceInternal;
+import java.util.regex.Pattern;
+import java.lang.annotation.Annotation;
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.Formatter;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+/**
+ * Contains abstractions for enforcing {@link RestrictedBindingSource}.
+ *
+ * <p>Enforcement happens in two phases:
+ *
+ * <ol>
+ *   <li>Data structures for enforcement are built during Binder configuration. {@link
+ *       PermitMapConstruction} encapsulates this process, and the {@link PermitMap} is the end
+ *       result.
+ *   <li>Restrictions are enforced by checking each binding for violations with {@link #check},
+ *       which uses the {@link PermitMap}(s) built during Binder configuration.
+ * </ol>
+ *
+ * <p>Note: None of this is thread-safe because it's only used while the Injector is being built,
+ * which happens on a single thread.
+ *
+ */
+public final class BindingSourceRestriction {
+    private BindingSourceRestriction() {}
+
+    private static final Logger logger = Logger.getLogger(RestrictedBindingSource.class.getName());
+
+    /** Mapping between an element source and its permit annotations. */
+    interface PermitMap {
+        ImmutableSet<Class<? extends Annotation>> getPermits(ElementSource elementSource);
+
+        void clear();
+    }
+
+    /** Returns a suggestion for how a restricted binding should be created in case it's missing. */
+    public static Optional<String> getMissingImplementationSuggestion(
+            GuiceInternal guiceInternal, Key<?> key) {
+        checkNotNull(guiceInternal);
+        RestrictedBindingSource restriction = getRestriction(key);
+        if (restriction == null) {
+            return Optional.empty();
+        }
+        return Optional.of(
+                String.format(
+                        "%nHint: This key is restricted and cannot be bound directly. Restriction explanation:"
+                                + " %s",
+                        restriction.explanation()));
+    }
+
+    /**
+     * Returns all the restriction violations found on the given Module Elements, as error messages.
+     *
+     * <p>Note: Intended to be used on Module Elements, not Injector Elements, ie. the result of
+     * {@link Elements#getElements} not {@code Injector.getElements}. The Module Elements this check
+     * cares about are:
+     *
+     * <ul>
+     *   <li>Module Bindings, which are always explicit and always have an {@link ElementSource} (with
+     *       a Module Stack), unlike Injector Bindings, which may be implicit and bereft of an
+     *       ElementSource.
+     *   <li>{@link PrivateElements}, which represent the recursive case of this check. They contain a
+     *       list of elements that this check is recursively called on.
+     * </ul>
+     */
+    public static ImmutableList<Message> check(GuiceInternal guiceInternal, List<Element> elements) {
+        checkNotNull(guiceInternal);
+        ImmutableList<Message> errorMessages = check(elements);
+        // Clear all the permit maps after the checks are done.
+        elements.forEach(BindingSourceRestriction::clear);
+        return errorMessages;
+    }
+
+    private static ImmutableList<Message> check(List<Element> elements) {
+        ImmutableList.Builder<Message> errorMessagesBuilder = ImmutableList.builder();
+        for (Element element : elements) {
+            errorMessagesBuilder.addAll(check(element));
+        }
+        return errorMessagesBuilder.build();
+    }
+
+    private static ImmutableList<Message> check(Element element) {
+        return element.acceptVisitor(
+                new DefaultElementVisitor<ImmutableList<Message>>() {
+                    // Base case.
+                    @Override
+                    protected ImmutableList<Message> visitOther(Element element) {
+                        return ImmutableList.of();
+                    }
+                    // Base case.
+                    @Override
+                    public <T> ImmutableList<Message> visit(Binding<T> binding) {
+                        Optional<Message> errorMessage = check(binding);
+                        if (errorMessage.isPresent()) {
+                            return ImmutableList.of(errorMessage.get());
+                        }
+                        return ImmutableList.of();
+                    }
+                    // Recursive case.
+                    @Override
+                    public ImmutableList<Message> visit(PrivateElements privateElements) {
+                        return check(privateElements.getElements());
+                    }
+                });
+    }
+
+    private static Optional<Message> check(Binding<?> binding) {
+        Key<?> key = binding.getKey();
+        // Module Bindings are all explicit and have an ElementSource.
+        ElementSource elementSource = (ElementSource) binding.getSource();
+        RestrictedBindingSource restriction = getRestriction(key);
+        if (restriction == null) {
+            return Optional.empty();
+        }
+        ImmutableSet<Class<? extends Annotation>> permits = getAllPermits(elementSource);
+        ImmutableSet<Class<? extends Annotation>> acceptablePermits =
+                ImmutableSet.copyOf(restriction.permits());
+        boolean bindingPermitted = permits.stream().anyMatch(acceptablePermits::contains);
+        if (bindingPermitted || isExempt(elementSource, restriction.exemptModules())) {
+            return Optional.empty();
+        }
+        String violationMessage =
+                getViolationMessage(
+                        key, restriction.explanation(), acceptablePermits, key.getAnnotationType() != null);
+        if (restriction.restrictionLevel() == RestrictionLevel.WARNING) {
+            Formatter sourceFormatter = new Formatter();
+            Errors.formatSource(sourceFormatter, elementSource);
+            logger.log(Level.WARNING, violationMessage + "\n" + sourceFormatter);
+            return Optional.empty();
+        }
+        return Optional.of(new Message(elementSource, violationMessage));
+    }
+
+    private static String getViolationMessage(
+            Key<?> key,
+            String explanation,
+            ImmutableSet<Class<? extends Annotation>> acceptablePermits,
+            boolean annotationRestricted) {
+        return String.format(
+                "Unable to bind key: %s. One of the modules that created this binding has to be annotated"
+                        + " with one of %s, because the key's %s is annotated with @RestrictedBindingSource."
+                        + " %s",
+                key,
+                acceptablePermits.stream().map(a -> "@" + a.getName()).collect(toList()),
+                annotationRestricted ? "annotation" : "type",
+                explanation);
+    }
+
+    /** Get all permits on the element source chain. */
+    private static ImmutableSet<Class<? extends Annotation>> getAllPermits(
+            ElementSource elementSource) {
+        ImmutableSet.Builder<Class<? extends Annotation>> permitsBuilder = ImmutableSet.builder();
+        permitsBuilder.addAll(elementSource.moduleSource.getPermitMap().getPermits(elementSource));
+        if (elementSource.scanner != null) {
+            getPermits(elementSource.scanner.getClass()).forEach(permitsBuilder::add);
+        }
+        if (elementSource.getOriginalElementSource() != null
+                && elementSource.trustedOriginalElementSource) {
+            permitsBuilder.addAll(getAllPermits(elementSource.getOriginalElementSource()));
+        }
+        return permitsBuilder.build();
+    }
+
+    private static boolean isExempt(ElementSource elementSource, String exemptModulesRegex) {
+        if (exemptModulesRegex.isEmpty()) {
+            return false;
+        }
+        Pattern exemptModulePattern = Pattern.compile(exemptModulesRegex);
+        // TODO(b/156759807): Switch to Streams.stream (instead of inlining it).
+        return StreamSupport.stream(getAllModules(elementSource).spliterator(), false)
+                .anyMatch(moduleName -> exemptModulePattern.matcher(moduleName).matches());
+    }
+
+    private static Iterable<String> getAllModules(ElementSource elementSource) {
+        List<String> modules = elementSource.getModuleClassNames();
+        if (elementSource.getOriginalElementSource() == null
+                || !elementSource.trustedOriginalElementSource) {
+            return modules;
+        }
+        return Iterables.concat(modules, getAllModules(elementSource.getOriginalElementSource()));
+    }
+
+    private static void clear(Element element) {
+        element.acceptVisitor(
+                new DefaultElementVisitor<Void>() {
+                    // Base case.
+                    @Override
+                    protected Void visitOther(Element element) {
+                        Object source = element.getSource();
+                        // Some Module Elements, like Message, don't always have an ElementSource.
+                        if (source instanceof ElementSource) {
+                            clear((ElementSource) source);
+                        }
+                        return null;
+                    }
+                    // Recursive case.
+                    @Override
+                    public Void visit(PrivateElements privateElements) {
+                        privateElements.getElements().forEach(BindingSourceRestriction::clear);
+                        return null;
+                    }
+                });
+    }
+
+    private static void clear(ElementSource elementSource) {
+        while (elementSource != null) {
+            elementSource.moduleSource.getPermitMap().clear();
+            elementSource = elementSource.getOriginalElementSource();
+        }
+    }
+
+    /*
+     * Returns the restriction on the given key (null if there is none).
+     *
+     * If the key is annotated then only the annotation restriction matters, the type restriction is
+     * ignored (an annotated type is essentially a new type).
+     **/
+    private static RestrictedBindingSource getRestriction(Key<?> key) {
+        return key.getAnnotationType() == null
+                ? key.getTypeLiteral().getRawType().getAnnotation(RestrictedBindingSource.class)
+                : key.getAnnotationType().getAnnotation(RestrictedBindingSource.class);
+    }
+
+    /**
+     * Builds the map from each module to all the permit annotations on its module stack.
+     *
+     * <p>Bindings refer to the module that created them via a {@link ModuleSource}. The map built
+     * here maps a module's {@link ModuleSource} to all the {@link RestrictedBindingSource.Permit}
+     * annotations found on the path from the root of the module hierarchy to it. This path contains
+     * all the modules that transitively install the module (including the module itself). This path
+     * is also known as the module stack.
+     *
+     * <p>The map is built by piggybacking on the depth-first traversal of the module hierarchy during
+     * Binder configuration.
+     */
+    static final class PermitMapConstruction {
+        private static final class PermitMapImpl implements PermitMap {
+            Map<ModuleSource, ImmutableSet<Class<? extends Annotation>>> modulePermits;
+
+            @Override
+            public ImmutableSet<Class<? extends Annotation>> getPermits(ElementSource elementSource) {
+                return modulePermits.get(elementSource.moduleSource);
+            }
+
+            @Override
+            public void clear() {
+                modulePermits = null;
+            }
+        }
+
+        final Map<ModuleSource, ImmutableSet<Class<? extends Annotation>>> modulePermits =
+                new HashMap<>();
+        // Maintains the permits on the current module installation path.
+        ImmutableSet<Class<? extends Annotation>> currentModulePermits = ImmutableSet.of();
+        // Stack tracking the currentModulePermits during module traversal.
+        final Deque<ImmutableSet<Class<? extends Annotation>>> modulePermitsStack = new ArrayDeque<>();
+
+        final PermitMapImpl permitMap = new PermitMapImpl();
+
+        /**
+         * Returns a possibly unfinished map. The map should only be used after the construction is
+         * finished.
+         */
+        PermitMap getPermitMap() {
+            return permitMap;
+        }
+
+        /**
+         * Sets the permits on the current module installation path to the permits on the given module
+         * source so that subsequently installed modules may inherit them. Used only for method
+         * scanning, so that modules installed by scanners inherit permits from the method's module.
+         */
+        void restoreCurrentModulePermits(ModuleSource moduleSource) {
+            currentModulePermits = modulePermits.get(moduleSource);
+        }
+
+        /** Called by the Binder prior to entering a module's configure method. */
+        void pushModule(Class<?> module, ModuleSource moduleSource) {
+            List<Class<? extends Annotation>> newModulePermits =
+                    getPermits(module)
+                            .filter(permit -> !currentModulePermits.contains(permit))
+                            .collect(toList());
+            // Save the parent module's permits so that they can be restored when the Binder exits this
+            // new (child) module's configure method.
+            modulePermitsStack.push(currentModulePermits);
+            if (!newModulePermits.isEmpty()) {
+                currentModulePermits =
+                        ImmutableSet.<Class<? extends Annotation>>builder()
+                                .addAll(currentModulePermits)
+                                .addAll(newModulePermits)
+                                .build();
+            }
+            modulePermits.put(moduleSource, currentModulePermits);
+        }
+
+        /** Called by the Binder when it exits a module's configure method. */
+        void popModule() {
+            // Restore the parent module's permits.
+            currentModulePermits = modulePermitsStack.pop();
+        }
+
+        /** Finishes the {@link PermitMap}. Called by the Binder when all modules are installed. */
+        void finish() {
+            permitMap.modulePermits = modulePermits;
+        }
+
+        @VisibleForTesting
+        static boolean isElementSourceCleared(ElementSource elementSource) {
+            PermitMapImpl permitMap = (PermitMapImpl) elementSource.moduleSource.getPermitMap();
+            return permitMap.modulePermits == null;
+        }
+    }
+
+    private static Stream<? extends Class<? extends Annotation>> getPermits(Class<?> clazz) {
+        Stream<Annotation> annotations = Arrays.stream(clazz.getAnnotations());
+        // Pick up annotations on anonymous classes (e.g. new @Bar Foo() { ... }):
+        if (clazz.getAnnotatedSuperclass() != null) {
+            annotations =
+                    Stream.concat(
+                            annotations, Arrays.stream(clazz.getAnnotatedSuperclass().getAnnotations()));
+        }
+        return annotations
+                .map(Annotation::annotationType)
+                .filter(a -> a.isAnnotationPresent(RestrictedBindingSource.Permit.class));
+    }
+}

src/main/java/com/google/inject/spi/ElementSource.java

@@ -4,41 +4,35 @@ import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.inject.internal.util.StackTraceElements;
 import com.google.inject.internal.util.StackTraceElements.InMemoryStackTraceElement;
-
 import java.util.List;
 
 /**
- * Contains information about where and how an {@link Element element} was
+ * Contains information about where and how an {@link Element element} was bound.
- * bound.
- * <p>
- * The {@link #getDeclaringSource() declaring source} refers to a location in
- * source code that defines the Guice {@link Element element}. For example, if
- * the element is created from a method annotated by {@literal @Provides}, the
- * declaring source of element would be the method itself.
- * <p>
- * The {@link #getStackTrace()} refers to the sequence of calls ends at one of
- * {@link com.google.inject.Binder} {@code bindXXX()} methods and eventually
- * defines the element. Note that {@link #getStackTrace()} lists
- * {@link StackTraceElement StackTraceElements} in reverse chronological order.
- * The first element (index zero) is the last method call and the last element
- * is the first method invocation. By default, the stack trace is not collected.
- * The default behavior can be changed by setting the
- * {@code guice_include_stack_traces} flag value. The value can be either
- * {@code OFF}, {@code ONLY_FOR_DECLARING_SOURCE} or {@code COMPLETE}. Note that
- * collecting stack traces for every binding can cause a performance hit when
- * the injector is created.
- * <p>
- * The sequence of class names of {@link com.google.inject.Module modules}
- * involved in the element creation can be retrieved by
- * {@link #getModuleClassNames()}. Similar to {@link #getStackTrace()}, the
- * order is reverse chronological. The first module (index 0) is the module that
- * installs the {@link Element element}. The last module is the root module.
- * <p>
- * In order to support the cases where a Guice {@link Element element} is
- * created from another Guice {@link Element element} (original) (e.g., by
- * {@link Element#applyTo}), it also provides a reference to the original
- * element source ({@link #getOriginalElementSource()}).
  *
+ * <p>The {@link #getDeclaringSource() declaring source} refers to a location in source code that
+ * defines the Guice {@link Element element}. For example, if the element is created from a method
+ * annotated by {@literal @Provides}, the declaring source of element would be the method itself.
+ *
+ * <p>The {@link #getStackTrace()} refers to the sequence of calls ends at one of {@link
+ * com.google.inject.Binder} {@code bindXXX()} methods and eventually defines the element. Note that
+ * {@link #getStackTrace()} lists {@link StackTraceElement StackTraceElements} in reverse
+ * chronological order. The first element (index zero) is the last method call and the last element
+ * is the first method invocation. By default, the stack trace is not collected. The default
+ * behavior can be changed by setting the {@code guice_include_stack_traces} flag value. The value
+ * can be either {@code OFF}, {@code ONLY_FOR_DECLARING_SOURCE} or {@code COMPLETE}. Note that
+ * collecting stack traces for every binding can cause a performance hit when the injector is
+ * created.
+ *
+ * <p>The sequence of class names of {@link com.google.inject.Module modules} involved in the
+ * element creation can be retrieved by {@link #getModuleClassNames()}. Similar to {@link
+ * #getStackTrace()}, the order is reverse chronological. The first module (index 0) is the module
+ * that installs the {@link Element element}. The last module is the root module.
+ *
+ * <p>In order to support the cases where a Guice {@link Element element} is created from another
+ * Guice {@link Element element} (original) (e.g., by {@link Element#applyTo}), it also provides a
+ * reference to the original element source ({@link #getOriginalElementSource()}).
+ *
+ * @since 4.0
  */
 public final class ElementSource {
 
@@ -46,36 +40,63 @@ public final class ElementSource {
      * The {@link ElementSource source} of element that this element created from (if there is any),
      * otherwise {@code null}.
      */
-    private final ElementSource originalElementSource;
+    final ElementSource originalElementSource;
 
     /**
-     * The {@link ModuleSource source} of module creates the element.
+     * Wheather the originalElementSource was set externaly (untrusted) or by Guice internals
-     */
+     * (trusted).
-    private final ModuleSource moduleSource;
-
-    private final InMemoryStackTraceElement[] partialCallStack;
-
-    private final Object declaringSource;
-
-    /**
-     * Creates a new {@link ElementSource} from the given parameters.
      *
-     * @param originalSource The source of element that this element created from (if there is
+     * <p>External code can set the originalElementSource to an arbitrary ElementSource via
+     * Binder.withSource(ElementSource), thereby spoofing the element origin.
+     */
+    final boolean trustedOriginalElementSource;
+
+    /** The {@link ModuleSource source} of module creates the element. */
+    final ModuleSource moduleSource;
+
+    /**
+     * The partial call stack that starts at the last module {@link Module#Configure(Binder)
+     * configure(Binder)} call. The value is empty if stack trace collection is off.
+     */
+    final InMemoryStackTraceElement[] partialCallStack;
+
+    /**
+     * Refers to a single location in source code that causes the element creation. It can be any
+     * object such as {@link Constructor}, {@link Method}, {@link Field}, {@link StackTraceElement},
+     * etc. For example, if the element is created from a method annotated by {@literal @Provides},
+     * the declaring source of element would be the method itself.
+     */
+    final Object declaringSource;
+
+    /** The scanner that created this binding (if it was created by a scanner). */
+    final ModuleAnnotatedMethodScanner scanner;
+
+    /**
+     * Creates a new {@ElementSource} from the given parameters.
+     *
+     * @param originalSource The source of element that this element was created from (if there is
      *     any), otherwise {@code null}.
      * @param declaringSource the source (in)directly declared the element.
      * @param moduleSource the moduleSource when the element is bound
      * @param partialCallStack the partial call stack from the top module to where the element is
      *     bound
      */
-    ElementSource(ElementSource originalSource, Object declaringSource,
+    ElementSource(
-                  ModuleSource moduleSource, StackTraceElement[] partialCallStack) {
+            ElementSource originalSource,
+            boolean trustedOriginalSource,
+            Object declaringSource,
+            ModuleSource moduleSource,
+            StackTraceElement[] partialCallStack,
+            ModuleAnnotatedMethodScanner scanner) {
         Preconditions.checkNotNull(declaringSource, "declaringSource cannot be null.");
         Preconditions.checkNotNull(moduleSource, "moduleSource cannot be null.");
         Preconditions.checkNotNull(partialCallStack, "partialCallStack cannot be null.");
         this.originalElementSource = originalSource;
+        this.trustedOriginalElementSource = trustedOriginalSource;
         this.declaringSource = declaringSource;
         this.moduleSource = moduleSource;
         this.partialCallStack = StackTraceElements.convertToInMemoryStackTraceElement(partialCallStack);
+        this.scanner = scanner;
     }
 
     /**
@@ -87,20 +108,20 @@ public final class ElementSource {
     }
 
     /**
-     * Returns a single location in source code that defines the element. It can be any object
+     * Returns a single location in source code that defines the element. It can be any object such as
-     * such as {@link java.lang.reflect.Constructor}, {@link java.lang.reflect.Method},
+     * {@link java.lang.reflect.Constructor}, {@link java.lang.reflect.Method}, {@link
-     * {@link java.lang.reflect.Field}, {@link StackTraceElement}, etc. For
+     * java.lang.reflect.Field}, {@link StackTraceElement}, etc. For example, if the element is
-     * example, if the element is created from a method annotated by {@literal @Provides}, the
+     * created from a method annotated by {@literal @Provides}, the declaring source of element would
-     * declaring source of element would be the method itself.
+     * be the method itself.
      */
     public Object getDeclaringSource() {
         return declaringSource;
     }
 
     /**
-     * Returns the class names of modules involved in creating this {@link Element}. The first
+     * Returns the class names of modules involved in creating this {@link Element}. The first element
-     * element (index 0) is the class name of module that defined the element, and the last element
+     * (index 0) is the class name of module that defined the element, and the last element is the
-     * is the class name of root module.
+     * class name of root module.
      */
     public List<String> getModuleClassNames() {
         return moduleSource.getModuleClassNames();
@@ -110,18 +131,18 @@ public final class ElementSource {
      * Returns the position of {@link com.google.inject.Module#configure configure(Binder)} method
      * call in the {@link #getStackTrace stack trace} for modules that their classes returned by
      * {@link #getModuleClassNames}. For example, if the stack trace looks like the following:
-     * <p>
+     *
-     * {@code
+     * <ol>
-     * 0 - Binder.bind(),
+     *   <li>{@code Binder.bind()}
-     * 1 - ModuleTwo.configure(),
+     *   <li>{@code ModuleTwo.configure()}
-     * 2 - Binder.install(),
+     *   <li>{@code Binder.install()}
-     * 3 - ModuleOne.configure(),
+     *   <li>{@code ModuleOne.configure()}
-     * 4 - theRest().
+     *   <li>{@code theRest().
-     * }
+     * </ol>
-     * <p>
+     *
-     * 1 and 3 are returned.
+     * <p>1 and 3 are returned.
-     * <p>
+     *
-     * In the cases where stack trace is not available (i.e., the stack trace was not collected),
+     * <p>In the cases where stack trace is not available (i.e., the stack trace was not collected),
      * it returns -1 for all module positions.
      */
     public List<Integer> getModuleConfigurePositionsInStackTrace() {
@@ -140,11 +161,11 @@ public final class ElementSource {
 
     /**
      * Returns the sequence of method calls that ends at one of {@link com.google.inject.Binder}
-     * {@code bindXXX()} methods and eventually defines the element. Note that
+     * {@code bindXXX()} methods and eventually defines the element. Note that {@link #getStackTrace}
-     * this method lists {@link StackTraceElement StackTraceElements} in reverse
+     * lists {@link StackTraceElement StackTraceElements} in reverse chronological order. The first
-     * chronological order. The first element (index zero) is the last method call and the last
+     * element (index zero) is the last method call and the last element is the first method
-     * element is the first method invocation. In the cases where stack trace is not available
+     * invocation. In the cases where stack trace is not available (i.e.,the stack trace was not
-     * (i.e.,the stack trace was not collected), it returns an empty array.
+     * collected), it returns an empty array.
      */
     public StackTraceElement[] getStackTrace() {
         int modulesCallStackSize = moduleSource.getStackTraceSize();
@@ -152,15 +173,16 @@ public final class ElementSource {
         int size = moduleSource.getStackTraceSize() + chunkSize;
         StackTraceElement[] callStack = new StackTraceElement[size];
         System.arraycopy(
-                StackTraceElements.convertToStackTraceElement(partialCallStack), 0, callStack, 0,
+                StackTraceElements.convertToStackTraceElement(partialCallStack),
+                0,
+                callStack,
+                0,
                 chunkSize);
         System.arraycopy(moduleSource.getStackTrace(), 0, callStack, chunkSize, modulesCallStackSize);
         return callStack;
     }
 
-    /**
+    /** Returns {@code getDeclaringSource().toString()} value. */
-     * Returns {@code getDeclaringSource().toString()} value.
-     */
     @Override
     public String toString() {
         return getDeclaringSource().toString();

src/main/java/com/google/inject/spi/Elements.java

@@ -1,6 +1,11 @@
 package com.google.inject.spi;
 
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.inject.internal.InternalFlags.getIncludeStackTraceOption;
+
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
@@ -24,15 +29,15 @@ import com.google.inject.internal.BindingBuilder;
 import com.google.inject.internal.ConstantBindingBuilderImpl;
 import com.google.inject.internal.Errors;
 import com.google.inject.internal.ExposureBuilder;
+import com.google.inject.internal.GuiceInternal;
 import com.google.inject.internal.InternalFlags.IncludeStackTraceOption;
-import com.google.inject.internal.Messages;
 import com.google.inject.internal.MoreTypes;
 import com.google.inject.internal.PrivateElementsImpl;
+import com.google.inject.internal.ProviderMethod;
 import com.google.inject.internal.ProviderMethodsModule;
 import com.google.inject.internal.util.SourceProvider;
 import com.google.inject.internal.util.StackTraceElements;
 import com.google.inject.matcher.Matcher;
-
 import java.lang.annotation.Annotation;
 import java.util.Arrays;
 import java.util.Collection;
@@ -41,9 +46,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import static com.google.common.base.Preconditions.checkArgument;
-import static com.google.inject.internal.InternalFlags.getIncludeStackTraceOption;
-
 /**
  * Exposes elements of a module so they can be inspected, validated or {@link
  * Element#applyTo(Binder) rewritten}.
@@ -52,7 +54,7 @@ import static com.google.inject.internal.InternalFlags.getIncludeStackTraceOptio
 public final class Elements {
 
     private static final BindingTargetVisitor<Object, Object> GET_INSTANCE_VISITOR =
-            new DefaultBindingTargetVisitor<>() {
+            new DefaultBindingTargetVisitor<Object, Object>() {
                 @Override
                 public Object visit(InstanceBinding<?> binding) {
                     return binding.getInstance();
@@ -64,54 +66,56 @@ public final class Elements {
                 }
             };
 
-    /**
+    /** Records the elements executed by {@code modules}. */
-     * Records the elements executed by {@code modules}.
-     */
     public static List<Element> getElements(Module... modules) {
         return getElements(Stage.DEVELOPMENT, Arrays.asList(modules));
     }
 
-    /**
+    /** Records the elements executed by {@code modules}. */
-     * Records the elements executed by {@code modules}.
-     */
     public static List<Element> getElements(Stage stage, Module... modules) {
         return getElements(stage, Arrays.asList(modules));
     }
 
-    /**
+    /** Records the elements executed by {@code modules}. */
-     * Records the elements executed by {@code modules}.
-     */
     public static List<Element> getElements(Iterable<? extends Module> modules) {
         return getElements(Stage.DEVELOPMENT, modules);
     }
 
-    /**
+    /** Records the elements executed by {@code modules}. */
-     * Records the elements executed by {@code modules}.
-     */
     public static List<Element> getElements(Stage stage, Iterable<? extends Module> modules) {
         RecordingBinder binder = new RecordingBinder(stage);
         for (Module module : modules) {
             binder.install(module);
         }
         binder.scanForAnnotatedMethods();
-        for (RecordingBinder child : binder.privateBinders) {
+        for (RecordingBinder child : binder.privateBindersForScanning) {
             child.scanForAnnotatedMethods();
         }
+        binder.permitMapConstruction.finish();
         // Free the memory consumed by the stack trace elements cache
         StackTraceElements.clearCache();
         return Collections.unmodifiableList(binder.elements);
     }
 
+    // TODO(user): Consider moving the RecordingBinder to com.google.inject.internal and removing these
+    // internal 'friend' methods.
     /**
-     * Returns the module composed of {@code elements}.
+     * Internal version of Binder.withSource for establishing a trusted ElementSource chain for
+     * source-restricting bindings that are re-written using {@link Element#applyTo}.
+     *
+     * <p>Using Binder.withSource is not trustworthy because it's a public API that external users can
+     * use to spoof the original ElementSource of a binding by calling withSource(bogusElementSource).
+     *
+     * @since 5.0
      */
-    public static Module getModule(final Iterable<? extends Element> elements) {
+    public static Binder withTrustedSource(
-        return new ElementsAsModule(elements);
+            GuiceInternal guiceInternal, Binder binder, Object source) {
+        checkNotNull(guiceInternal);
+        if (binder instanceof RecordingBinder) {
+            return ((RecordingBinder) binder).withTrustedSource(source);
         }
-
+        // Preserve existing (untrusted) behavior for non-standard Binder implementations.
-    @SuppressWarnings("unchecked")
+        return binder.withSource(source);
-    static <T> BindingTargetVisitor<T, T> getInstanceVisitor() {
-        return (BindingTargetVisitor<T, T>) GET_INSTANCE_VISITOR;
     }
 
     private static class ElementsAsModule implements Module {
@@ -129,13 +133,21 @@ public final class Elements {
         }
     }
 
+    /** Returns the module composed of {@code elements}. */
+    public static Module getModule(final Iterable<? extends Element> elements) {
+        return new ElementsAsModule(elements);
+    }
+
+    @SuppressWarnings("unchecked")
+    static <T> BindingTargetVisitor<T, T> getInstanceVisitor() {
+        return (BindingTargetVisitor<T, T>) GET_INSTANCE_VISITOR;
+    }
+
     private static class ModuleInfo {
-        private final Binder binder;
         private final ModuleSource moduleSource;
         private final boolean skipScanning;
 
-        private ModuleInfo(Binder binder, ModuleSource moduleSource, boolean skipScanning) {
+        private ModuleInfo(ModuleSource moduleSource, boolean skipScanning) {
-            this.binder = binder;
             this.moduleSource = moduleSource;
             this.skipScanning = skipScanning;
         }
@@ -148,19 +160,28 @@ public final class Elements {
         private final Object source;
         private final SourceProvider sourceProvider;
         private final Set<ModuleAnnotatedMethodScanner> scanners;
-        /**
+        /** The binder where exposed bindings will be created */
-         * The binder where exposed bindings will be created
-         */
         private final RecordingBinder parent;
+
         private final PrivateElementsImpl privateElements;
-        /**
+        /** All children private binders, so we can scan through them. */
-         * All children private binders, so we can scan through them.
+        private final List<RecordingBinder> privateBindersForScanning;
-         */
+
-        private final List<RecordingBinder> privateBinders;
+        private final BindingSourceRestriction.PermitMapConstruction permitMapConstruction;
-        /**
+
-         * The current modules stack
+        /** The current modules stack */
-         */
         private ModuleSource moduleSource = null;
+        /**
+         * The current scanner.
+         *
+         * <p>Note that scanners cannot nest, ie. a scanner cannot install a module that requires
+         * scanning - except the built-in @Provides* methods. The built-in scanner isn't tracked by this
+         * variable, only custom scanners are.
+         */
+        private ModuleAnnotatedMethodScanner scannerSource = null;
+
+        private ModuleAnnotatedMethodScanner currentScanner = null;
+        private boolean trustedSource = false;
 
         private RecordingBinder(Stage stage) {
             this.stage = stage;
@@ -168,47 +189,59 @@ public final class Elements {
             this.scanners = Sets.newLinkedHashSet();
             this.elements = Lists.newArrayList();
             this.source = null;
-            this.sourceProvider = SourceProvider.DEFAULT_INSTANCE.plusSkippedClasses(
+            this.sourceProvider =
-                    Elements.class, RecordingBinder.class, AbstractModule.class,
+                    SourceProvider.DEFAULT_INSTANCE.plusSkippedClasses(
-                    ConstantBindingBuilderImpl.class, AbstractBindingBuilder.class, BindingBuilder.class);
+                            Elements.class,
+                            RecordingBinder.class,
+                            AbstractModule.class,
+                            ConstantBindingBuilderImpl.class,
+                            AbstractBindingBuilder.class,
+                            BindingBuilder.class);
             this.parent = null;
             this.privateElements = null;
-            this.privateBinders = Lists.newArrayList();
+            this.privateBindersForScanning = Lists.newArrayList();
+            this.permitMapConstruction = new BindingSourceRestriction.PermitMapConstruction();
         }
 
-        /**
+        /** Creates a recording binder that's backed by {@code prototype}. */
-         * Creates a recording binder that's backed by {@code prototype}.
-         */
         private RecordingBinder(
-                RecordingBinder prototype, Object source, SourceProvider sourceProvider) {
+                RecordingBinder prototype,
+                Object source,
+                SourceProvider sourceProvider,
+                boolean trustedSource) {
             checkArgument(source == null ^ sourceProvider == null);
 
             this.stage = prototype.stage;
             this.modules = prototype.modules;
             this.elements = prototype.elements;
             this.scanners = prototype.scanners;
+            this.currentScanner = prototype.currentScanner;
             this.source = source;
+            this.trustedSource = trustedSource;
             this.moduleSource = prototype.moduleSource;
             this.sourceProvider = sourceProvider;
             this.parent = prototype.parent;
             this.privateElements = prototype.privateElements;
-            this.privateBinders = prototype.privateBinders;
+            this.privateBindersForScanning = prototype.privateBindersForScanning;
+            this.permitMapConstruction = prototype.permitMapConstruction;
+            this.scannerSource = prototype.scannerSource;
         }
 
-        /**
+        /** Creates a private recording binder. */
-         * Creates a private recording binder.
-         */
         private RecordingBinder(RecordingBinder parent, PrivateElementsImpl privateElements) {
             this.stage = parent.stage;
             this.modules = Maps.newLinkedHashMap();
-            this.scanners = Sets.newLinkedHashSet(parent.scanners);
+            this.scanners = Sets.newLinkedHashSet();
+            this.currentScanner = parent.currentScanner;
             this.elements = privateElements.getElementsMutable();
             this.source = parent.source;
             this.moduleSource = parent.moduleSource;
             this.sourceProvider = parent.sourceProvider;
             this.parent = parent;
             this.privateElements = privateElements;
-            this.privateBinders = parent.privateBinders;
+            this.privateBindersForScanning = parent.privateBindersForScanning;
+            this.permitMapConstruction = parent.permitMapConstruction;
+            this.scannerSource = parent.scannerSource;
         }
 
         @Override
@@ -219,19 +252,23 @@ public final class Elements {
         @Override
         @SuppressWarnings("unchecked") // it is safe to use the type literal for the raw type
         public void requestInjection(Object instance) {
+            checkNotNull(instance, "instance");
             requestInjection((TypeLiteral<Object>) TypeLiteral.get(instance.getClass()), instance);
         }
 
         @Override
         public <T> void requestInjection(TypeLiteral<T> type, T instance) {
-            elements.add(new InjectionRequest<>(getElementSource(), MoreTypes.canonicalizeForKey(type),
+            checkNotNull(instance, "instance");
-                    instance));
+            elements.add(
+                    new InjectionRequest<T>(
+                            getElementSource(), MoreTypes.canonicalizeForKey(type), instance));
         }
 
         @Override
         public <T> MembersInjector<T> getMembersInjector(final TypeLiteral<T> typeLiteral) {
-            final MembersInjectorLookup<T> element = new MembersInjectorLookup<>(getElementSource(),
+            final MembersInjectorLookup<T> element =
-                    MoreTypes.canonicalizeForKey(typeLiteral));
+                    new MembersInjectorLookup<T>(
+                            getElementSource(), MoreTypes.canonicalizeForKey(typeLiteral));
             elements.add(element);
             return element.getMembersInjector();
         }
@@ -247,8 +284,8 @@ public final class Elements {
         }
 
         @Override
-        public void bindListener(Matcher<? super Binding<?>> bindingMatcher,
+        public void bindListener(
-                                 ProvisionListener... listeners) {
+                Matcher<? super Binding<?>> bindingMatcher, ProvisionListener... listeners) {
             elements.add(new ProvisionListenerBinding(getElementSource(), bindingMatcher, listeners));
         }
 
@@ -260,13 +297,12 @@ public final class Elements {
         }
 
         /**
-         * Applies all scanners to the modules we've installed. We skip certain
+         * Applies all scanners to the modules we've installed. We skip certain PrivateModules because
-         * PrivateModules because store them in more than one Modules map and only
+         * store them in more than one Modules map and only want to process them through one of the
-         * want to process them through one of the maps.  (They're stored in both
+         * maps. (They're stored in both maps to prevent a module from being installed more than once.)
-         * maps to prevent a module from being installed more than once.)
          */
         void scanForAnnotatedMethods() {
-            for (ModuleAnnotatedMethodScanner scanner : scanners) {
+            Iterable<ModuleAnnotatedMethodScanner> scanners = getAllScanners();
             // Note: we must iterate over a copy of the modules because calling install(..)
             // will mutate modules, otherwise causing a ConcurrentModificationException.
             for (Map.Entry<Module, ModuleInfo> entry : Maps.newLinkedHashMap(modules).entrySet()) {
@@ -275,9 +311,12 @@ public final class Elements {
                 if (info.skipScanning) {
                     continue;
                 }
+                for (ModuleAnnotatedMethodScanner scanner : scanners) {
+                    currentScanner = scanner;
                     moduleSource = entry.getValue().moduleSource;
+                    permitMapConstruction.restoreCurrentModulePermits(moduleSource);
                     try {
-                        info.binder.install(ProviderMethodsModule.forModule(module, scanner));
+                        install(ProviderMethodsModule.forModule(module, scanner));
                     } catch (RuntimeException e) {
                         Collection<Message> messages = Errors.getMessagesFromThrowable(e);
                         if (!messages.isEmpty()) {
@@ -293,35 +332,50 @@ public final class Elements {
 
         @Override
         public void install(Module module) {
-            if (!modules.containsKey(module)) {
+            // Ignore duplicate installations of the same module instance.
+            if (modules.containsKey(module)) {
+                return;
+            }
+            // Whether the module installed is a ProviderMethodModule for a custom scanner.
+            boolean customScanner = false;
+            Class<?> newModuleClass = null;
             RecordingBinder binder = this;
-                boolean unwrapModuleSource = false;
             // Update the module source for the new module
             if (module instanceof ProviderMethodsModule) {
+                ProviderMethodsModule providerMethodsModule = (ProviderMethodsModule) module;
+                if (!providerMethodsModule.isScanningBuiltInProvidesMethods()) {
+                    scannerSource = providerMethodsModule.getScanner();
+                    customScanner = true;
+                }
                 // There are two reason's we'd want to get the module source in a ProviderMethodsModule.
                 // ModuleAnnotatedMethodScanner lets users scan their own modules for @Provides-like
                 // bindings.  If they install the module at a top-level, then moduleSource can be null.
                 // Also, if they pass something other than 'this' to it, we'd have the wrong source.
-                    Object delegate = ((ProviderMethodsModule) module).getDelegateModule();
+                Class<?> delegateClass = providerMethodsModule.getDelegateModuleClass();
                 if (moduleSource == null
-                            || !moduleSource.getModuleClassName().equals(delegate.getClass().getName())) {
+                        || !moduleSource.getModuleClassName().equals(delegateClass.getName())) {
-                        moduleSource = getModuleSource(delegate);
+                    newModuleClass = delegateClass;
-                        unwrapModuleSource = true;
                 }
             } else {
-                    moduleSource = getModuleSource(module);
+                if (moduleScanning()) {
-                    unwrapModuleSource = true;
+                    forbidNestedScannerMethods(module);
+                }
+                newModuleClass = module.getClass();
+            }
+            if (newModuleClass != null) {
+                moduleSource = getModuleSource(newModuleClass);
+                permitMapConstruction.pushModule(newModuleClass, moduleSource);
             }
             boolean skipScanning = false;
             if (module instanceof PrivateModule) {
                 binder = (RecordingBinder) binder.newPrivateBinder();
                 // Store the module in the private binder too so we scan for it.
-                    binder.modules.put(module, new ModuleInfo(binder, moduleSource, false));
+                binder.modules.put(module, new ModuleInfo(moduleSource, false));
                 skipScanning = true; // don't scan this module in the parent's module set.
             }
             // Always store this in the parent binder (even if it was a private module)
             // so that we know not to process it again, and so that scanners inherit down.
-                modules.put(module, new ModuleInfo(binder, moduleSource, skipScanning));
+            modules.put(module, new ModuleInfo(moduleSource, skipScanning));
             try {
                 module.configure(binder);
             } catch (RuntimeException e) {
@@ -334,10 +388,44 @@ public final class Elements {
             }
             binder.install(ProviderMethodsModule.forModule(module));
             // We are done with this module, so undo module source change
-                if (unwrapModuleSource) {
+            if (newModuleClass != null) {
                 moduleSource = moduleSource.getParent();
+                permitMapConstruction.popModule();
+            }
+            // Only wipe the scannerSource once custom scanner installation is finished. This way all
+            // bindings created by the custom scanner will have it as their scanner source, including
+            // bindings created by the built-in scanner scanning @Provides* methods in modules installed
+            // by the custom scanner.
+            if (customScanner) {
+                scannerSource = null;
             }
         }
+
+        private void forbidNestedScannerMethods(Module module) {
+            for (ModuleAnnotatedMethodScanner scanner : getAllScanners()) {
+                ProviderMethodsModule providerMethodsModule =
+                        (ProviderMethodsModule) ProviderMethodsModule.forModule(module, scanner);
+                for (ProviderMethod<?> method : providerMethodsModule.getProviderMethods(this)) {
+                    addError(
+                            "Scanner %s is installing a module with %s method. Installing modules with custom "
+                                    + "provides methods from a ModuleAnnotatedMethodScanner is not supported.",
+                            currentScanner, method.getAnnotation().annotationType().getCanonicalName());
+                }
+            }
+        }
+
+        /**
+         * Get all scanners registered in this binder and its ancestors.
+         *
+         * <p>Should only be called during module scanning, because at that point registering new
+         * scanners is forbidden.
+         */
+        private Iterable<ModuleAnnotatedMethodScanner> getAllScanners() {
+            if (privateElements == null) {
+                return scanners;
+            }
+            // Private binders have their own set of scanners and they inherit from their parent.
+            return Iterables.concat(scanners, parent.getAllScanners());
         }
 
         @Override
@@ -347,13 +435,13 @@ public final class Elements {
 
         @Override
         public void addError(String message, Object... arguments) {
-            elements.add(new Message(getElementSource(), Messages.format(message, arguments)));
+            elements.add(new Message(getElementSource(), Errors.format(message, arguments)));
         }
 
         @Override
         public void addError(Throwable t) {
             String message = "An exception was caught and reported. Message: " + t.getMessage();
-            elements.add(new Message(ImmutableList.of(getElementSource()), message, t));
+            elements.add(new Message(ImmutableList.of((Object) getElementSource()), message, t));
         }
 
         @Override
@@ -363,7 +451,9 @@ public final class Elements {
 
         @Override
         public <T> AnnotatedBindingBuilder<T> bind(Key<T> key) {
-            return new BindingBuilder<>(this, elements, getElementSource(), MoreTypes.canonicalizeKey(key));
+            BindingBuilder<T> builder =
+                    new BindingBuilder<T>(this, elements, getElementSource(), MoreTypes.canonicalizeKey(key));
+            return builder;
         }
 
         @Override
@@ -399,14 +489,24 @@ public final class Elements {
         }
 
         @Override
-        public void convertToTypes(Matcher<? super TypeLiteral<?>> typeMatcher,
+        public void convertToTypes(
-                                   TypeConverter converter) {
+                Matcher<? super TypeLiteral<?>> typeMatcher, TypeConverter converter) {
             elements.add(new TypeConverterBinding(getElementSource(), typeMatcher, converter));
         }
 
         @Override
         public RecordingBinder withSource(final Object source) {
-            return source == this.source ? this : new RecordingBinder(this, source, null);
+            return source == this.source
+                    ? this
+                    : new RecordingBinder(
+                    this, source, /* sourceProvider = */ null, /* trustedSource = */ false);
+        }
+
+        public RecordingBinder withTrustedSource(final Object source) {
+            return source == this.source
+                    ? this
+                    : new RecordingBinder(
+                    this, source, /* sourceProvider = */ null, /* trustedSource = */ true);
         }
 
         @Override
@@ -417,15 +517,19 @@ public final class Elements {
             }
 
             SourceProvider newSourceProvider = sourceProvider.plusSkippedClasses(classesToSkip);
-            return new RecordingBinder(this, null, newSourceProvider);
+            return new RecordingBinder(
+                    this, /* source = */ null, newSourceProvider, /* trustedSource = */ false);
         }
 
         @Override
         public PrivateBinder newPrivateBinder() {
             PrivateElementsImpl privateElements = new PrivateElementsImpl(getElementSource());
             RecordingBinder binder = new RecordingBinder(this, privateElements);
-            privateBinders.add(binder);
             elements.add(privateElements);
+            // Don't want to scan private modules installed by scanners.
+            if (!moduleScanning()) {
+                privateBindersForScanning.add(binder);
+            }
             return binder;
         }
 
@@ -451,6 +555,13 @@ public final class Elements {
 
         @Override
         public void scanModulesForAnnotatedMethods(ModuleAnnotatedMethodScanner scanner) {
+            if (moduleScanning()) {
+                addError(
+                        "Attempting to register ModuleAnnotatedMethodScanner %s from scanner %s. Scanners are"
+                                + " not allowed to register other scanners.",
+                        currentScanner, scanner);
+                return;
+            }
             scanners.add(scanner);
             elements.add(new ModuleAnnotatedMethodScannerBinding(getElementSource(), scanner));
         }
@@ -472,26 +583,26 @@ public final class Elements {
 
         private <T> AnnotatedElementBuilder exposeInternal(Key<T> key) {
             if (privateElements == null) {
-                addError("Cannot expose %s on a standard binder. "
+                addError(
-                        + "Exposed bindings are only applicable to private binders.", key);
+                        "Cannot expose %s on a standard binder. "
+                                + "Exposed bindings are only applicable to private binders.",
+                        key);
                 return new AnnotatedElementBuilder() {
                     @Override
-                    public void annotatedWith(Class<? extends Annotation> annotationType) {
+                    public void annotatedWith(Class<? extends Annotation> annotationType) {}
-                    }
 
                     @Override
-                    public void annotatedWith(Annotation annotation) {
+                    public void annotatedWith(Annotation annotation) {}
-                    }
                 };
             }
 
             ExposureBuilder<T> builder =
-                    new ExposureBuilder<>(this, getElementSource(), MoreTypes.canonicalizeKey(key));
+                    new ExposureBuilder<T>(this, getElementSource(), MoreTypes.canonicalizeKey(key));
             privateElements.addExposureBuilder(builder);
             return builder;
         }
 
-        private ModuleSource getModuleSource(Object module) {
+        private ModuleSource getModuleSource(Class<?> module) {
             StackTraceElement[] partialCallStack;
             if (getIncludeStackTraceOption() == IncludeStackTraceOption.COMPLETE) {
                 partialCallStack = getPartialCallStack(new Throwable().getStackTrace());
@@ -499,7 +610,7 @@ public final class Elements {
                 partialCallStack = new StackTraceElement[0];
             }
             if (moduleSource == null) {
-                return new ModuleSource(module, partialCallStack);
+                return new ModuleSource(module, partialCallStack, permitMapConstruction.getPermitMap());
             }
             return moduleSource.createChild(module, partialCallStack);
         }
@@ -518,8 +629,8 @@ public final class Elements {
                 declaringSource = originalSource.getDeclaringSource();
             }
             IncludeStackTraceOption stackTraceOption = getIncludeStackTraceOption();
-            if (stackTraceOption == IncludeStackTraceOption.COMPLETE ||
+            if (stackTraceOption == IncludeStackTraceOption.COMPLETE
-                    (stackTraceOption == IncludeStackTraceOption.ONLY_FOR_DECLARING_SOURCE
+                    || (stackTraceOption == IncludeStackTraceOption.ONLY_FOR_DECLARING_SOURCE
                     && declaringSource == null)) {
                 callStack = new Throwable().getStackTrace();
             }
@@ -528,10 +639,20 @@ public final class Elements {
             }
             if (declaringSource == null) {
                 // So 'source' and 'originalSource' are null otherwise declaringSource has some value
-                if (stackTraceOption == IncludeStackTraceOption.COMPLETE ||
+                if (stackTraceOption == IncludeStackTraceOption.COMPLETE
-                        stackTraceOption == IncludeStackTraceOption.ONLY_FOR_DECLARING_SOURCE) {
+                        || stackTraceOption == IncludeStackTraceOption.ONLY_FOR_DECLARING_SOURCE) {
                     // With the above conditions and assignments 'callStack' is non-null
-                    declaringSource = sourceProvider.get(callStack);
+                    StackTraceElement callingSource = sourceProvider.get(callStack);
+                    // If we've traversed past all reasonable sources and into our internal code, then we
+                    // don't know the source.
+                    if (callingSource
+                            .getClassName()
+                            .equals("com.google.inject.internal.InjectorShell$Builder")
+                            && callingSource.getMethodName().equals("build")) {
+                        declaringSource = SourceProvider.UNKNOWN_SOURCE;
+                    } else {
+                        declaringSource = callingSource;
+                    }
                 } else { // or if (stackTraceOption == IncludeStackTraceOptions.OFF)
                     // As neither 'declaring source' nor 'call stack' is available use 'module source'
                     declaringSource = sourceProvider.getFromClassNames(moduleSource.getModuleClassNames());
@@ -539,13 +660,18 @@ public final class Elements {
             }
             // Build the binding call stack
             return new ElementSource(
-                    originalSource, declaringSource, moduleSource, partialCallStack);
+                    originalSource,
+                    trustedSource,
+                    declaringSource,
+                    moduleSource,
+                    partialCallStack,
+                    scannerSource);
         }
 
         /**
          * Removes the {@link #moduleSource} call stack from the beginning of current call stack. It
-         * also removes the last two elements in order to make {@link #install(Module)} the last call
+         * also removes the last two elements in order to make {@link #install(Module)} the last call in
-         * in the call stack.
+         * the call stack.
          */
         private StackTraceElement[] getPartialCallStack(StackTraceElement[] callStack) {
             int toSkip = 0;
@@ -560,6 +686,11 @@ public final class Elements {
             return partialCallStack;
         }
 
+        /** Returns if the binder is in the module scanning phase. */
+        private boolean moduleScanning() {
+            return currentScanner != null;
+        }
+
         @Override
         public String toString() {
             return "Binder";

src/main/java/com/google/inject/spi/ErrorDetail.java

@@ -0,0 +1,127 @@
+package com.google.inject.spi;
+
+import com.google.common.base.Objects;
+import com.google.common.collect.ImmutableList;
+import com.google.inject.internal.Messages;
+import java.io.Serializable;
+import java.util.Formatter;
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * Details about a single Guice error and supports formatting itself in the context of other Guice
+ * errors.
+ *
+ * <p>WARNING: The class and its APIs are still experimental and subject to change.
+ *
+ * @since 5.0
+ */
+public abstract class ErrorDetail<SelfT extends ErrorDetail<SelfT>> implements Serializable {
+  private final String message;
+  private final ImmutableList<Object> sources;
+  private final Throwable cause;
+
+  protected ErrorDetail(String message, List<Object> sources, Throwable cause) {
+    this.message = message;
+    this.sources = ImmutableList.copyOf(sources);
+    this.cause = cause;
+  }
+
+  /**
+   * Returns true if this error can be merged with the {@code otherError} and formatted together.
+   *
+   * <p>By default this return false and implementations that support merging with other errors
+   * should override this method.
+   */
+  public boolean isMergeable(ErrorDetail<?> otherError) {
+    return false;
+  }
+
+  /**
+   * Formats this error along with other errors that are mergeable with this error.
+   *
+   * <p>{@code mergeableErrors} is a list that contains all other errors that are reported in the
+   * same exception that are considered to be mergable with this error base on result of calling
+   * {@link #isMergeable}. The list will be empty if non of the other errors are mergable with this
+   * error.
+   *
+   * <p>Formatted error has the following structure:
+   *
+   * <ul>
+   *   <li>Summary of the error
+   *   <li>Details about the error such as the source of the error
+   *   <li>Hints for fixing the error if available
+   *   <li>Link to the documentation on this error in greater detail
+   *
+   * @param index index for this error
+   * @param mergeableErrors list of errors that are mergeable with this error
+   * @param formatter for printing the error message
+   */
+  public final void format(int index, List<ErrorDetail<?>> mergeableErrors, Formatter formatter) {
+    String id = getErrorIdentifier().map(s -> "[" + Messages.redBold(s) + "]: ").orElse("");
+    formatter.format("%s) %s%s%n", index, id, getMessage());
+    formatDetail(mergeableErrors, formatter);
+    // TODO(b/151482394): Output potiential fixes for the error
+    Optional<String> learnMoreLink = getLearnMoreLink();
+    if (learnMoreLink.isPresent()) {
+      formatter.format("%n%s%n", Messages.bold("Learn more:"));
+      formatter.format("  %s%n", Messages.underline(learnMoreLink.get()));
+    }
+  }
+
+  /**
+   * Formats the detail of this error message along with other errors that are mergeable with this
+   * error. This is called from {@link #format}.
+   *
+   * <p>{@code mergeableErrors} is a list that contains all other errors that are reported in the
+   * same exception that are considered to be mergable with this error base on result of calling
+   * {@link #isMergeable}. The list will be empty if non of the other errors are mergable with this
+   * error.
+   *
+   * @param mergeableErrors list of errors that are mergeable with this error
+   * @param formatter for printing the error message
+   */
+  protected abstract void formatDetail(List<ErrorDetail<?>> mergeableErrors, Formatter formatter);
+
+  /**
+   * Returns an optional link to additional documentation about this error to be included in the
+   * formatted error message.
+   */
+  protected Optional<String> getLearnMoreLink() {
+    return Optional.empty();
+  }
+
+  /** Returns an optional string identifier for this error. */
+  protected Optional<String> getErrorIdentifier() {
+    return Optional.empty();
+  }
+
+  public String getMessage() {
+    return message;
+  }
+
+  public List<Object> getSources() {
+    return sources;
+  }
+
+  public Throwable getCause() {
+    return cause;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hashCode(message, cause, sources);
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (!(o instanceof ErrorDetail)) {
+      return false;
+    }
+    ErrorDetail<?> e = (ErrorDetail<?>) o;
+    return message.equals(e.message) && Objects.equal(cause, e.cause) && sources.equals(e.sources);
+  }
+
+  /** Returns a new instance of the same {@link ErrorDetail} with updated sources. */
+  public abstract SelfT withSources(List<Object> newSources);
+}

src/main/java/com/google/inject/spi/Message.java

@@ -1,19 +1,40 @@
+/*
+ * Copyright (C) 2006 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package com.google.inject.spi;
 
-import com.google.common.base.Objects;
-import com.google.common.collect.ImmutableList;
-import com.google.inject.Binder;
-import com.google.inject.internal.Messages;
-import com.google.inject.internal.util.SourceProvider;
-
-import java.util.List;
-
 import static com.google.common.base.Preconditions.checkNotNull;
 
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Iterables;
+import com.google.inject.Binder;
+import com.google.inject.internal.ErrorId;
+import com.google.inject.internal.Errors;
+import com.google.inject.internal.GenericErrorDetail;
+import com.google.inject.internal.GuiceInternal;
+import com.google.inject.internal.util.SourceProvider;
+import java.io.ObjectStreamException;
+import java.io.Serializable;
+import java.util.List;
+
 /**
  * An error message and the context in which it occured. Messages are usually created internally by
  * Guice and its extensions. Messages can be created explicitly in a module using {@link
  * com.google.inject.Binder#addError(Throwable) addError()} statements:
+ *
  * <pre>
  *     try {
  *       bindPropertiesFromFile();
@@ -21,21 +42,36 @@ import static com.google.common.base.Preconditions.checkNotNull;
  *       addError(e);
  *     }</pre>
  *
+ * @author crazybob@google.com (Bob Lee)
  */
-public final class Message implements Element {
+public final class Message implements Serializable, Element {
+    private final ErrorId errorId;
+    private final ErrorDetail<?> errorDetail;
 
-    private final String message;
+    /** @since 5.0 */
-
+    public Message(GuiceInternal internalOnly, ErrorId errorId, ErrorDetail<?> errorDetail) {
-    private final Throwable cause;
+        checkNotNull(internalOnly);
-
+        this.errorId = errorId;
-    private final List<Object> sources;
+        this.errorDetail = errorDetail;
-
-    public Message(List<Object> sources, String message, Throwable cause) {
-        this.sources = ImmutableList.copyOf(sources);
-        this.message = checkNotNull(message, "message");
-        this.cause = cause;
     }
 
+    private Message(ErrorId errorId, ErrorDetail<?> errorDetail) {
+        this.errorId = errorId;
+        this.errorDetail = errorDetail;
+    }
+
+    /** @since 2.0 */
+    public Message(ErrorId errorId, List<Object> sources, String message, Throwable cause) {
+        this.errorId = errorId;
+        this.errorDetail = new GenericErrorDetail(errorId, message, sources, cause);
+    }
+
+    /** @since 2.0 */
+    public Message(List<Object> sources, String message, Throwable cause) {
+        this(ErrorId.OTHER, sources, message, cause);
+    }
+
+    /** @since 4.0 */
     public Message(String message, Throwable cause) {
         this(ImmutableList.of(), message, cause);
     }
@@ -48,45 +84,57 @@ public final class Message implements Element {
         this(ImmutableList.of(), message, null);
     }
 
+    /**
+     * Returns details about this error message.
+     *
+     * @since 5.0
+     */
+    public ErrorDetail<?> getErrorDetail() {
+        return errorDetail;
+    }
+
     @Override
     public String getSource() {
+        List<Object> sources = errorDetail.getSources();
         return sources.isEmpty()
                 ? SourceProvider.UNKNOWN_SOURCE.toString()
-                : Messages.convert(sources.get(sources.size() - 1)).toString();
+                : Errors.convert(Iterables.getLast(sources)).toString();
     }
 
+    /** @since 2.0 */
     public List<Object> getSources() {
-        return sources;
+        return errorDetail.getSources();
     }
 
-    /**
+    /** Gets the error message text. */
-     * Gets the error message text.
-     */
     public String getMessage() {
-        return message;
+        return errorDetail.getMessage();
     }
 
+    /** @since 2.0 */
     @Override
     public <T> T acceptVisitor(ElementVisitor<T> visitor) {
         return visitor.visit(this);
     }
 
     /**
-     * Returns the throwable that caused this message, or {@code null} if this
+     * Returns the throwable that caused this message, or {@code null} if this message was not caused
-     * message was not caused by a throwable.
+     * by a throwable.
+     *
+     * @since 2.0
      */
     public Throwable getCause() {
-        return cause;
+        return errorDetail.getCause();
     }
 
     @Override
     public String toString() {
-        return message;
+        return errorDetail.getMessage();
     }
 
     @Override
     public int hashCode() {
-        return Objects.hashCode(message, cause, sources);
+        return errorDetail.hashCode();
     }
 
     @Override
@@ -95,12 +143,39 @@ public final class Message implements Element {
             return false;
         }
         Message e = (Message) o;
-        return Objects.equal(message, e.message) && Objects.equal(cause, e.cause) && Objects.equal(sources, e.sources);
+        return errorDetail.equals(e.errorDetail);
     }
 
+    /** @since 2.0 */
     @Override
     public void applyTo(Binder binder) {
         binder.withSource(getSource()).addError(this);
     }
 
+    /**
+     * Returns a copy of this {@link Message} with its sources replaced.
+     *
+     * @since 5.0
+     */
+    public Message withSource(List<Object> newSources) {
+        return new Message(errorId, errorDetail.withSources(newSources));
+    }
+
+    /**
+     * When serialized, we convert the error detail to a {@link GenericErrorDetail} with string
+     * sources. This hurts our formatting, but it guarantees that the receiving end will be able to
+     * read the message.
+     */
+    private Object writeReplace() throws ObjectStreamException {
+        Object[] sourcesAsStrings = getSources().toArray();
+        for (int i = 0; i < sourcesAsStrings.length; i++) {
+            sourcesAsStrings[i] = Errors.convert(sourcesAsStrings[i]).toString();
+        }
+        return new Message(
+                errorId,
+                new GenericErrorDetail(
+                        errorId, getMessage(), ImmutableList.copyOf(sourcesAsStrings), getCause()));
+    }
+
+    private static final long serialVersionUID = 0;
 }

src/main/java/com/google/inject/spi/ModuleAnnotatedMethodScannerBinding.java

@@ -1,10 +1,9 @@
 package com.google.inject.spi;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+
 import com.google.inject.Binder;
 import com.google.inject.internal.Errors;
-import com.google.inject.internal.Messages;
-
-import static com.google.common.base.Preconditions.checkNotNull;
 
 /**
  * Represents a call to {@link Binder#scanModulesForAnnotatedMethods} in a module.
@@ -18,6 +17,7 @@ public final class ModuleAnnotatedMethodScannerBinding implements Element {
         this.scanner = checkNotNull(scanner, "scanner");
     }
 
+    @Override
     public Object getSource() {
         return source;
     }
@@ -26,17 +26,23 @@ public final class ModuleAnnotatedMethodScannerBinding implements Element {
         return scanner;
     }
 
+    @Override
     public <T> T acceptVisitor(ElementVisitor<T> visitor) {
         return visitor.visit(this);
     }
 
+    @Override
     public void applyTo(Binder binder) {
         binder.withSource(getSource()).scanModulesForAnnotatedMethods(scanner);
     }
 
     @Override
     public String toString() {
-        return scanner + " which scans for " + scanner.annotationClasses()
+        return scanner
-                + " (bound at " + Messages.convert(source) + ")";
+                + " which scans for "
+                + scanner.annotationClasses()
+                + " (bound at "
+                + Errors.convert(source)
+                + ")";
     }
 }

src/main/java/com/google/inject/spi/ModuleSource.java

@@ -2,30 +2,33 @@ package com.google.inject.spi;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
-import com.google.inject.Binder;
 import com.google.inject.Module;
 import com.google.inject.internal.util.StackTraceElements;
 import com.google.inject.internal.util.StackTraceElements.InMemoryStackTraceElement;
-
 import java.util.List;
 
 /**
  * Associated to a {@link Module module}, provides the module class name, the parent module {@link
  * ModuleSource source}, and the call stack that ends just before the module {@link
- * Module#configure(Binder)} method invocation.
+ * Module#configure(Binder) configure(Binder)} method invocation.
  */
 final class ModuleSource {
 
-    /**
+    /** The class name of module that this {@link ModuleSource} associated to. */
-     * The class name of module that this {@link ModuleSource} associated to.
-     */
     private final String moduleClassName;
 
-    /**
+    /** The parent {@link ModuleSource module source}. */
-     * The parent {@link ModuleSource module source}.
-     */
     private final ModuleSource parent;
 
+    /**
+     * Permit map created by the binder that installed this module.
+     *
+     * <p>The permit map is a binder-scoped object, but it's saved here because these maps have to
+     * outlive the binders that created them in order to be used at injector creation, and there isn't
+     * a 'BinderSource' object.
+     */
+    private final BindingSourceRestriction.PermitMap permitMap;
+
     /**
      * The chunk of call stack that starts from the parent module {@link Module#configure(Binder)
      * configure(Binder)} call and ends just before the module {@link Module#configure(Binder)
@@ -37,31 +40,38 @@ final class ModuleSource {
     /**
      * Creates a new {@link ModuleSource} with a {@literal null} parent.
      *
-     * @param module           the corresponding module
+     * @param moduleClass the corresponding module
      * @param partialCallStack the chunk of call stack that starts from the parent module {@link
      *     Module#configure(Binder) configure(Binder)} call and ends just before the module {@link
      *     Module#configure(Binder) configure(Binder)} method invocation
      */
-    ModuleSource(Object module, StackTraceElement[] partialCallStack) {
+    ModuleSource(
-        this(null, module, partialCallStack);
+            Class<?> moduleClass,
+            StackTraceElement[] partialCallStack,
+            BindingSourceRestriction.PermitMap permitMap) {
+        this(null, moduleClass, partialCallStack, permitMap);
     }
 
     /**
      * Creates a new {@link ModuleSource} Object.
      *
      * @param parent the parent module {@link ModuleSource source}
-     * @param module           the corresponding module
+     * @param moduleClass the corresponding module
      * @param partialCallStack the chunk of call stack that starts from the parent module {@link
      *     Module#configure(Binder) configure(Binder)} call and ends just before the module {@link
      *     Module#configure(Binder) configure(Binder)} method invocation
      */
     private ModuleSource(
-      /* @Nullable */ ModuleSource parent, Object module, StackTraceElement[] partialCallStack) {
+            ModuleSource parent,
-        Preconditions.checkNotNull(module, "module cannot be null.");
+            Class<?> moduleClass,
+            StackTraceElement[] partialCallStack,
+            BindingSourceRestriction.PermitMap permitMap) {
+        Preconditions.checkNotNull(moduleClass, "module cannot be null.");
         Preconditions.checkNotNull(partialCallStack, "partialCallStack cannot be null.");
         this.parent = parent;
-        this.moduleClassName = module.getClass().getName();
+        this.moduleClassName = moduleClass.getName();
         this.partialCallStack = StackTraceElements.convertToInMemoryStackTraceElement(partialCallStack);
+        this.permitMap = permitMap;
     }
 
     /**
@@ -83,9 +93,7 @@ final class ModuleSource {
         return StackTraceElements.convertToStackTraceElement(partialCallStack);
     }
 
-    /**
+    /** Returns the size of partial call stack if stack trace collection is on otherwise zero. */
-     * Returns the size of partial call stack if stack trace collection is on otherwise zero.
-     */
     int getPartialCallStackSize() {
         return partialCallStack.length;
     }
@@ -93,18 +101,16 @@ final class ModuleSource {
     /**
      * Creates and returns a child {@link ModuleSource} corresponding to the {@link Module module}.
      *
-     * @param module           the corresponding module
+     * @param moduleClass the corresponding module
      * @param partialCallStack the chunk of call stack that starts from the parent module {@link
      *     Module#configure(Binder) configure(Binder)} call and ends just before the module {@link
      *     Module#configure(Binder) configure(Binder)} method invocation
      */
-    ModuleSource createChild(Object module, StackTraceElement[] partialCallStack) {
+    ModuleSource createChild(Class<?> moduleClass, StackTraceElement[] partialCallStack) {
-        return new ModuleSource(this, module, partialCallStack);
+        return new ModuleSource(this, moduleClass, partialCallStack, permitMap);
     }
 
-    /**
+    /** Returns the parent module {@link ModuleSource source}. */
-     * Returns the parent module {@link ModuleSource source}.
-     */
     ModuleSource getParent() {
         return parent;
     }
@@ -167,4 +173,9 @@ final class ModuleSource {
         }
         return callStack;
     }
+
+    /** Returns the permit map created by the binder that installed this module. */
+    BindingSourceRestriction.PermitMap getPermitMap() {
+        return permitMap;
+    }
 }

src/main/java/com/google/inject/spi/TypeConverterBinding.java

@@ -1,18 +1,20 @@
 package com.google.inject.spi;
 
-import com.google.inject.Binder;
-import com.google.inject.TypeLiteral;
-import com.google.inject.internal.Messages;
-import com.google.inject.matcher.Matcher;
-
 import static com.google.common.base.Preconditions.checkNotNull;
 
+import com.google.inject.Binder;
+import com.google.inject.TypeLiteral;
+import com.google.inject.internal.Errors;
+import com.google.inject.matcher.Matcher;
+
 /**
- * Registration of type converters for matching target types. Instances are created
+ * Registration of type converters for matching target types. Instances are created explicitly in a
- * explicitly in a module using {@link com.google.inject.Binder#convertToTypes(Matcher,
+ * module using {@link com.google.inject.Binder#convertToTypes(Matcher, TypeConverter)
- * TypeConverter) convertToTypes()} statements:
+ * convertToTypes()} statements:
+ *
  * <pre>
- *     convertToTypes(Matchers.only(TypeLiteral.get(DateTime.class)), new DateTimeConverter());</pre>
+ *     convertToTypes(Matchers.only(TypeLiteral.get(DateTime.class)), new DateTimeConverter());
+ * </pre>
  *
  */
 public final class TypeConverterBinding implements Element {
@@ -20,13 +22,15 @@ public final class TypeConverterBinding implements Element {
     private final Matcher<? super TypeLiteral<?>> typeMatcher;
     private final TypeConverter typeConverter;
 
-    public TypeConverterBinding(Object source, Matcher<? super TypeLiteral<?>> typeMatcher,
+    /** @since 3.0 */
-                                TypeConverter typeConverter) {
+    public TypeConverterBinding(
+            Object source, Matcher<? super TypeLiteral<?>> typeMatcher, TypeConverter typeConverter) {
         this.source = checkNotNull(source, "source");
         this.typeMatcher = checkNotNull(typeMatcher, "typeMatcher");
         this.typeConverter = checkNotNull(typeConverter, "typeConverter");
     }
 
+    @Override
     public Object getSource() {
         return source;
     }
@@ -39,17 +43,23 @@ public final class TypeConverterBinding implements Element {
         return typeConverter;
     }
 
+    @Override
     public <T> T acceptVisitor(ElementVisitor<T> visitor) {
         return visitor.visit(this);
     }
 
+    @Override
     public void applyTo(Binder binder) {
         binder.withSource(getSource()).convertToTypes(typeMatcher, typeConverter);
     }
 
     @Override
     public String toString() {
-        return typeConverter + " which matches " + typeMatcher
+        return typeConverter
-                + " (bound at " + Messages.convert(source) + ")";
+                + " which matches "
+                + typeMatcher
+                + " (bound at "
+                + Errors.convert(source)
+                + ")";
     }
 }

src/main/java/com/google/inject/util/Modules.java

@@ -9,13 +9,12 @@ import com.google.common.collect.Sets;
 import com.google.inject.AbstractModule;
 import com.google.inject.Binder;
 import com.google.inject.Binding;
-import com.google.inject.Inject;
 import com.google.inject.Key;
 import com.google.inject.Module;
 import com.google.inject.PrivateBinder;
 import com.google.inject.PrivateModule;
 import com.google.inject.Scope;
-import com.google.inject.internal.Messages;
+import com.google.inject.internal.Errors;
 import com.google.inject.spi.DefaultBindingScopingVisitor;
 import com.google.inject.spi.DefaultElementVisitor;
 import com.google.inject.spi.Element;
@@ -24,7 +23,6 @@ import com.google.inject.spi.Elements;
 import com.google.inject.spi.ModuleAnnotatedMethodScannerBinding;
 import com.google.inject.spi.PrivateElements;
 import com.google.inject.spi.ScopeBinding;
-
 import java.lang.annotation.Annotation;
 import java.util.Arrays;
 import java.util.LinkedHashSet;
@@ -37,18 +35,23 @@ import java.util.Set;
  *
  */
 public final class Modules {
+    private Modules() {}
+
     public static final Module EMPTY_MODULE = new EmptyModule();
 
-    private Modules() {
+    private static class EmptyModule implements Module {
+        @Override
+        public void configure(Binder binder) {}
     }
 
     /**
-     * Returns a builder that creates a module that overlays override modules over the given
+     * Returns a builder that creates a module that overlays override modules over the given modules.
-     * modules. If a key is bound in both sets of modules, only the binding from the override modules
+     * If a key is bound in both sets of modules, only the binding from the override modules is kept.
-     * is kept. If a single {@link PrivateModule} is supplied or all elements are from
+     * If a single {@link PrivateModule} is supplied or all elements are from a single {@link
-     * a single {@link PrivateBinder}, then this will overwrite the private bindings.
+     * PrivateBinder}, then this will overwrite the private bindings. Otherwise, private bindings will
-     * Otherwise, private bindings will not be overwritten unless they are exposed.
+     * not be overwritten unless they are exposed. This can be used to replace the bindings of a
-     * This can be used to replace the bindings of a production module with test bindings:
+     * production module with test bindings:
+     *
      * <pre>
      * Module functionalTestModule
      *     = Modules.override(new ProductionModule()).with(new TestModule());
@@ -62,13 +65,20 @@ public final class Modules {
         return override(Arrays.asList(modules));
     }
 
+    /** @deprecated there's no reason to use {@code Modules.override()} without any arguments. */
+    @Deprecated
+    public static OverriddenModuleBuilder override() {
+        return override(Arrays.asList());
+    }
+
     /**
-     * Returns a builder that creates a module that overlays override modules over the given
+     * Returns a builder that creates a module that overlays override modules over the given modules.
-     * modules. If a key is bound in both sets of modules, only the binding from the override modules
+     * If a key is bound in both sets of modules, only the binding from the override modules is kept.
-     * is kept. If a single {@link PrivateModule} is supplied or all elements are from
+     * If a single {@link PrivateModule} is supplied or all elements are from a single {@link
-     * a single {@link PrivateBinder}, then this will overwrite the private bindings.
+     * PrivateBinder}, then this will overwrite the private bindings. Otherwise, private bindings will
-     * Otherwise, private bindings will not be overwritten unless they are exposed.
+     * not be overwritten unless they are exposed. This can be used to replace the bindings of a
-     * This can be used to replace the bindings of a production module with test bindings:
+     * production module with test bindings:
+     *
      * <pre>
      * Module functionalTestModule
      *     = Modules.override(getProductionModules()).with(getTestModules());
@@ -84,61 +94,38 @@ public final class Modules {
 
     /**
      * Returns a new module that installs all of {@code modules}.
+     *
+     * <p>Although sometimes helpful, this method is rarely necessary. Most Guice APIs accept multiple
+     * arguments or (like {@code install()}) can be called repeatedly. Where possible, external APIs
+     * that require a single module should similarly be adapted to permit multiple modules.
      */
     public static Module combine(Module... modules) {
         return combine(ImmutableSet.copyOf(modules));
     }
 
+    /** @deprecated there's no need to "combine" one module; just install it directly. */
+    @Deprecated
+    public static Module combine(Module module) {
+        return module;
+    }
+
+    /** @deprecated this method call is effectively a no-op, just remove it. */
+    @Deprecated
+    public static Module combine() {
+        return EMPTY_MODULE;
+    }
+
     /**
      * Returns a new module that installs all of {@code modules}.
+     *
+     * <p>Although sometimes helpful, this method is rarely necessary. Most Guice APIs accept multiple
+     * arguments or (like {@code install()}) can be called repeatedly. Where possible, external APIs
+     * that require a single module should similarly be adapted to permit multiple modules.
      */
     public static Module combine(Iterable<? extends Module> modules) {
         return new CombinedModule(modules);
     }
 
-    private static Module extractScanners(Iterable<Element> elements) {
-        final List<ModuleAnnotatedMethodScannerBinding> scanners = Lists.newArrayList();
-        ElementVisitor<Void> visitor = new DefaultElementVisitor<>() {
-            @Override
-            public Void visit(ModuleAnnotatedMethodScannerBinding binding) {
-                scanners.add(binding);
-                return null;
-            }
-        };
-        for (Element element : elements) {
-            element.acceptVisitor(visitor);
-        }
-        return new AbstractModule() {
-            @Override
-            protected void configure() {
-                for (ModuleAnnotatedMethodScannerBinding scanner : scanners) {
-                    scanner.applyTo(binder());
-                }
-            }
-        };
-    }
-
-    /**
-     * See the EDSL example at {@link Modules#override(Module[]) override()}.
-     */
-    public interface OverriddenModuleBuilder {
-
-        /**
-         * See the EDSL example at {@link Modules#override(Module[]) override()}.
-         */
-        Module with(Module... overrides);
-
-        /**
-         * See the EDSL example at {@link Modules#override(Module[]) override()}.
-         */
-        Module with(Iterable<? extends Module> overrides);
-    }
-
-    private static class EmptyModule implements Module {
-        public void configure(Binder binder) {
-        }
-    }
-
     private static class CombinedModule implements Module {
         final Set<Module> modulesSet;
 
@@ -146,6 +133,7 @@ public final class Modules {
             this.modulesSet = ImmutableSet.copyOf(modules);
         }
 
+        @Override
         public void configure(Binder binder) {
             binder = binder.skipSources(getClass());
             for (Module module : modulesSet) {
@@ -154,17 +142,39 @@ public final class Modules {
         }
     }
 
+    /** See the EDSL example at {@link Modules#override(Module[]) override()}. */
+    public interface OverriddenModuleBuilder {
+
+        /** See the EDSL example at {@link Modules#override(Module[]) override()}. */
+        Module with(Module... overrides);
+
+        /** @deprecated there's no reason to use {@code .with()} without any arguments. */
+        @Deprecated
+        public Module with();
+
+        /** See the EDSL example at {@link Modules#override(Module[]) override()}. */
+        Module with(Iterable<? extends Module> overrides);
+    }
+
     private static final class RealOverriddenModuleBuilder implements OverriddenModuleBuilder {
         private final ImmutableSet<Module> baseModules;
 
+        // TODO(diamondm) checkArgument(!baseModules.isEmpty())?
         private RealOverriddenModuleBuilder(Iterable<? extends Module> baseModules) {
             this.baseModules = ImmutableSet.copyOf(baseModules);
         }
 
+        @Override
         public Module with(Module... overrides) {
             return with(Arrays.asList(overrides));
         }
 
+        @Override
+        public Module with() {
+            return with(Arrays.asList());
+        }
+
+        @Override
         public Module with(Iterable<? extends Module> overrides) {
             return new OverrideModule(overrides, baseModules);
         }
@@ -174,6 +184,7 @@ public final class Modules {
         private final ImmutableSet<Module> overrides;
         private final ImmutableSet<Module> baseModules;
 
+        // TODO(diamondm) checkArgument(!overrides.isEmpty())?
         OverrideModule(Iterable<? extends Module> overrides, ImmutableSet<Module> baseModules) {
             this.overrides = ImmutableSet.copyOf(overrides);
             this.baseModules = baseModules;
@@ -191,7 +202,8 @@ public final class Modules {
                 Element element = Iterables.getOnlyElement(baseElements);
                 if (element instanceof PrivateElements) {
                     PrivateElements privateElements = (PrivateElements) element;
-                    PrivateBinder privateBinder = baseBinder.newPrivateBinder().withSource(privateElements.getSource());
+                    PrivateBinder privateBinder =
+                            baseBinder.newPrivateBinder().withSource(privateElements.getSource());
                     for (Key<?> exposed : privateElements.getExposedKeys()) {
                         privateBinder.withSource(privateElements.getExposedSource(exposed)).expose(exposed);
                     }
@@ -203,7 +215,9 @@ public final class Modules {
             final Binder binder = baseBinder.skipSources(this.getClass());
             final LinkedHashSet<Element> elements = new LinkedHashSet<>(baseElements);
             final Module scannersModule = extractScanners(elements);
-            final List<Element> overrideElements = Elements.getElements(currentStage(),
+            final List<Element> overrideElements =
+                    Elements.getElements(
+                            currentStage(),
                             ImmutableList.<Module>builder().addAll(overrides).add(scannersModule).build());
 
             final Set<Key<?>> overriddenKeys = Sets.newHashSet();
@@ -245,7 +259,9 @@ public final class Modules {
                         // Record when a scope instance is used in a binding
                         Scope scope = getScopeInstanceOrNull(binding);
                         if (scope != null) {
-                            scopeInstancesInUse.computeIfAbsent(scope, k -> Lists.newArrayList()).add(binding.getSource());
+                            scopeInstancesInUse
+                                    .computeIfAbsent(scope, k -> Lists.newArrayList())
+                                    .add(binding.getSource());
                         }
                     }
 
@@ -253,8 +269,8 @@ public final class Modules {
                 }
 
                 void rewrite(Binder binder, PrivateElements privateElements, Set<Key<?>> keysToSkip) {
-                    PrivateBinder privateBinder = binder.withSource(privateElements.getSource())
+                    PrivateBinder privateBinder =
-                            .newPrivateBinder();
+                            binder.withSource(privateElements.getSource()).newPrivateBinder();
 
                     Set<Key<?>> skippedExposes = Sets.newHashSet();
 
@@ -267,8 +283,7 @@ public final class Modules {
                     }
 
                     for (Element element : privateElements.getElements()) {
-                        if (element instanceof Binding
+                        if (element instanceof Binding && skippedExposes.remove(((Binding) element).getKey())) {
-                                && skippedExposes.remove(((Binding) element).getKey())) {
                             continue;
                         }
                         if (element instanceof PrivateElements) {
@@ -304,13 +319,15 @@ public final class Modules {
                     } else {
                         List<Object> usedSources = scopeInstancesInUse.get(scopeBinding.getScope());
                         if (usedSources != null) {
-                            StringBuilder sb = new StringBuilder(
+                            StringBuilder sb =
+                                    new StringBuilder(
                                             "The scope for @%s is bound directly and cannot be overridden.");
-                            sb.append("%n     original binding at ").append(Messages.convert(scopeBinding.getSource()));
+                            sb.append("%n     original binding at " + Errors.convert(scopeBinding.getSource()));
                             for (Object usedSource : usedSources) {
-                                sb.append("%n     bound directly at ").append(Messages.convert(usedSource));
+                                sb.append("%n     bound directly at " + Errors.convert(usedSource) + "");
                             }
-                            binder.withSource(overideBinding.getSource())
+                            binder
+                                    .withSource(overideBinding.getSource())
                                     .addError(sb.toString(), scopeBinding.getAnnotationType().getSimpleName());
                         }
                     }
@@ -320,7 +337,8 @@ public final class Modules {
         }
 
         private Scope getScopeInstanceOrNull(Binding<?> binding) {
-            return binding.acceptScopingVisitor(new DefaultBindingScopingVisitor<>() {
+            return binding.acceptScopingVisitor(
+                    new DefaultBindingScopingVisitor<Scope>() {
                         @Override
                         public Scope visitScope(Scope scope) {
                             return scope;
@@ -349,7 +367,34 @@ public final class Modules {
         }
     }
 
-    /** Returns a module that will configure the injector to require explicit bindings. */
+    private static Module extractScanners(Iterable<Element> elements) {
+        final List<ModuleAnnotatedMethodScannerBinding> scanners = Lists.newArrayList();
+        ElementVisitor<Void> visitor =
+                new DefaultElementVisitor<Void>() {
+                    @Override
+                    public Void visit(ModuleAnnotatedMethodScannerBinding binding) {
+                        scanners.add(binding);
+                        return null;
+                    }
+                };
+        for (Element element : elements) {
+            element.acceptVisitor(visitor);
+        }
+        return new AbstractModule() {
+            @Override
+            protected void configure() {
+                for (ModuleAnnotatedMethodScannerBinding scanner : scanners) {
+                    scanner.applyTo(binder());
+                }
+            }
+        };
+    }
+
+    /**
+     * Returns a module that will configure the injector to require explicit bindings.
+     *
+     * @since 4.2.3
+     */
     public static Module requireExplicitBindingsModule() {
         return new RequireExplicitBindingsModule();
     }
@@ -362,8 +407,8 @@ public final class Modules {
     }
 
     /**
-     * Returns a module that will configure the injector to require
+     * Returns a module that will configure the injector to require {@literal @}{@link Inject} on
-     * {@link Inject} on constructors.
+     * constructors.
      *
      * @see Binder#requireAtInjectOnConstructors
      */
@@ -382,6 +427,7 @@ public final class Modules {
      * Returns a module that will configure the injector to require an exactly matching binding
      * annotation.
      *
+     * @since 4.2.3
      * @see Binder#requireExactBindingAnnotations
      */
     public static Module requireExactBindingAnnotationsModule() {
@@ -395,7 +441,9 @@ public final class Modules {
         }
     }
 
-    /** Returns a module that will configure the injector to disable circular proxies. */
+    /**
+     * Returns a module that will configure the injector to disable circular proxies.
+     */
     public static Module disableCircularProxiesModule() {
         return new DisableCircularProxiesModule();
     }