Move ComponentDescriptor.Kind and ModuleDescriptor.Kind to top-level types, add some Javadoc for them, and make a few changes to code that uses them (or the annotations associated with them) to reduce direct hardcoded use of the enum values or annotation classes.

RELNOTES=n/a

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=223865157
diff --git a/java/dagger/internal/codegen/ModuleKind.java b/java/dagger/internal/codegen/ModuleKind.java
new file mode 100644
index 0000000..7087f88
--- /dev/null
+++ b/java/dagger/internal/codegen/ModuleKind.java
@@ -0,0 +1,115 @@
+/*
+ * Copyright (C) 2015 The Dagger Authors.
+ *
+ * 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 dagger.internal.codegen;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static dagger.internal.codegen.DaggerElements.getAnnotationMirror;
+import static dagger.internal.codegen.DaggerStreams.toImmutableSet;
+
+import com.google.auto.common.MoreElements;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
+import dagger.Module;
+import dagger.Provides;
+import dagger.producers.ProducerModule;
+import dagger.producers.Produces;
+import java.lang.annotation.Annotation;
+import java.util.EnumSet;
+import java.util.Optional;
+import java.util.Set;
+import javax.lang.model.element.AnnotationMirror;
+import javax.lang.model.element.TypeElement;
+
+/** Enumeration of the kinds of modules. */
+enum ModuleKind {
+  /** {@code @Module} */
+  MODULE(Module.class, Provides.class),
+
+  /** {@code @ProducerModule} */
+  PRODUCER_MODULE(ProducerModule.class, Produces.class);
+
+  /** Returns the annotations for modules of the given kinds. */
+  static ImmutableSet<Class<? extends Annotation>> annotationsFor(Set<ModuleKind> kinds) {
+    return kinds.stream().map(ModuleKind::annotation).collect(toImmutableSet());
+  }
+
+  /**
+   * Returns the kind of an annotated element if it is annotated with one of the module {@linkplain
+   * #annotation() annotations}.
+   *
+   * @throws IllegalArgumentException if the element is annotated with more than one of the module
+   *     annotations
+   */
+  static Optional<ModuleKind> forAnnotatedElement(TypeElement element) {
+    Set<ModuleKind> kinds = EnumSet.noneOf(ModuleKind.class);
+    for (ModuleKind kind : values()) {
+      if (MoreElements.isAnnotationPresent(element, kind.annotation())) {
+        kinds.add(kind);
+      }
+    }
+
+    if (kinds.size() > 1) {
+      throw new IllegalArgumentException(
+          element + " cannot be annotated with more than one of " + annotationsFor(kinds));
+    }
+    return kinds.stream().findAny();
+  }
+
+  private final Class<? extends Annotation> moduleAnnotation;
+  private final Class<? extends Annotation> methodAnnotation;
+
+  ModuleKind(
+      Class<? extends Annotation> moduleAnnotation, Class<? extends Annotation> methodAnnotation) {
+    this.moduleAnnotation = moduleAnnotation;
+    this.methodAnnotation = methodAnnotation;
+  }
+
+  /**
+   * Returns the annotation mirror for this module kind on the given type.
+   *
+   * @throws IllegalArgumentException if the annotation is not present on the type
+   */
+  AnnotationMirror getModuleAnnotation(TypeElement element) {
+    Optional<AnnotationMirror> result = getAnnotationMirror(element, moduleAnnotation);
+    checkArgument(
+        result.isPresent(), "annotation %s is not present on type %s", moduleAnnotation, element);
+    return result.get();
+  }
+
+  /** Returns the annotation that marks a module of this kind. */
+  Class<? extends Annotation> annotation() {
+    return moduleAnnotation;
+  }
+
+  /** Returns the annotation for binding methods on this type of module. */
+  // TODO(cgdecker): Validate how this is used... is it really correct? Producer modules can also
+  // have @Provides methods.
+  Class<? extends Annotation> methodAnnotation() {
+    return methodAnnotation;
+  }
+
+  /** Returns the kinds of modules that a module of this kind is allowed to include. */
+  ImmutableSet<ModuleKind> legalIncludedModuleKinds() {
+    switch (this) {
+      case MODULE:
+        return Sets.immutableEnumSet(MODULE);
+      case PRODUCER_MODULE:
+        return Sets.immutableEnumSet(MODULE, PRODUCER_MODULE);
+    }
+    throw new AssertionError(this);
+  }
+}