Add a @ProvidesInto{Set,Map,Optional} & MultibindingsScanner that allow users
to annotate methods in a Module as elements that can contribute to a
Multibinder, MapBinder, or OptionalBinder.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=86801706
diff --git a/extensions/multibindings/src/com/google/inject/multibindings/MapKey.java b/extensions/multibindings/src/com/google/inject/multibindings/MapKey.java
new file mode 100644
index 0000000..bcb6a3b
--- /dev/null
+++ b/extensions/multibindings/src/com/google/inject/multibindings/MapKey.java
@@ -0,0 +1,58 @@
+/**
+ * Copyright (C) 2015 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.multibindings;
+
+import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Allows users define customized key type annotations for map bindings by annotating an annotation
+ * of a {@code Map}'s key type. The custom key annotation can be applied to methods also annotated
+ * with {@literal @}{@link ProvidesIntoMap}.
+ *
+ * <p>A {@link StringMapKey} and {@link ClassMapKey} are provided for convenience with maps whose
+ * keys are strings or classes. For maps with enums or primitive types as keys, you must provide
+ * your own MapKey annotation, such as this one for an enum:
+ *
+ * <pre>
+ * {@literal @}MapKey(unwrapValue = true)
+ * {@literal @}Retention(RUNTIME)
+ * public {@literal @}interface MyCustomEnumKey {
+ * MyCustomEnum value();
+ * }
+ * </pre>
+ *
+ * You can also use the whole annotation as the key, if {@code unwrapValue=false}.
+ * When unwrapValue is false, the annotation type will be the key type for the injected map and
+ * the annotation instances will be the key values. If {@code unwrapValue=true}, the value() type
+ * will be the key type for injected map and the value() instances will be the keys values.
+ */
+@Documented
+@Target(ANNOTATION_TYPE)
+@Retention(RUNTIME)
+public @interface MapKey {
+ /**
+ * if {@code unwrapValue} is false, then the whole annotation will be the type and annotation
+ * instances will be the keys. If {@code unwrapValue} is true, the value() type of key type
+ * annotation will be the key type for injected map and the value instances will be the keys.
+ */
+ boolean unwrapValue();
+}