name: Feature Addition Request
description: I want to add a new feature
labels: ["type=addition"]
body:
  - type: markdown
    attributes:
      value: >
        Filing feature requests is one of the most popular ways to contribute to Guava.


        Be aware, though: most feature requests are not accepted, even if they're suggested by
        a full-time Guava team member. [Feedback](https://stackoverflow.com/a/4543114) from our

 *
 * @param <T> The interface whose features are to be enumerated.
 * @author George van den Driessche
 */
@GwtCompatible
public interface Feature<T> {
  /** Returns the set of features that are implied by this feature. */
  Set<Feature<? super T>> getImpliedFeatures();

  }

  enum ExampleDerivedFeature implements Feature<ExampleDerivedInterface> {
    DERIVED_FEATURE_1,
    DERIVED_FEATURE_2(ExampleBaseFeature.BASE_FEATURE_1),
    DERIVED_FEATURE_3,

    COMPOUND_DERIVED_FEATURE(
        DERIVED_FEATURE_1, DERIVED_FEATURE_2, ExampleBaseFeature.BASE_FEATURE_2);

    private Set<Feature<? super ExampleDerivedInterface>> implied;

    ExampleDerivedFeature(Feature<? super ExampleDerivedInterface>... implied) {

   * @return the implied set of features
   */
  public static Set<Feature<?>> impliedFeatures(Set<Feature<?>> features) {
    Set<Feature<?>> impliedSet = new LinkedHashSet<>();
    Queue<Feature<?>> queue = new ArrayDeque<>(features);
    while (!queue.isEmpty()) {
      Feature<?> feature = queue.remove();
      for (Feature<?> implied : feature.getImpliedFeatures()) {
        if (!features.contains(implied) && impliedSet.add(implied)) {

    // Copy this set, so we can modify it.
    Set<Feature<?>> features = Helpers.copyToSet(getFeatures());
    @SuppressWarnings("rawtypes") // class literals
    List<Class<? extends AbstractTester>> testers = getTesters();

    logger.fine(" Testing: " + name);

    // Split out all the specified sizes.
    Set<Feature<?>> sizesToTest = Helpers.<Feature<?>>copyToSet(CollectionSize.values());
    sizesToTest.retainAll(features);

@GwtCompatible
public enum SetFeature implements Feature<Set> {
  GENERAL_PURPOSE(CollectionFeature.GENERAL_PURPOSE);

  private final Set<Feature<? super Set>> implied;

  SetFeature(Feature<? super Set>... implied) {
    this.implied = Helpers.copyToSet(implied);
  }

  @Override
  public Set<Feature<? super Set>> getImpliedFeatures() {
    return implied;
  }

   */

  ANY(ZERO, ONE, SEVERAL);

  private final Set<Feature<? super Collection>> implied;
  private final @Nullable Integer numElements;

  CollectionSize(int numElements) {
    this.implied = Collections.emptySet();
    this.numElements = numElements;
  }

  CollectionSize(Feature<? super Collection>... implied) {
    // Keep the order here, so that PerCollectionSizeTestSuiteBuilder

          annotationClass.getDeclaringClass(),
          returnType.getComponentType());
    }
  }

  // This is public so that tests for Feature enums we haven't yet imagined
  // can reuse it.
  public static <E extends Enum<?> & Feature<?>> void assertGoodFeatureEnum(
      Class<E> featureEnumClass) {
    final Class<?>[] classes = featureEnumClass.getDeclaredClasses();
    for (Class<?> containedClass : classes) {

  }

  /**
   * To avoid infinite recursion, test suites with these marker features won't have derived suites
   * created for them.
   */
  enum NoRecurse implements Feature<@Nullable Void> {
    SUBMAP,
    DESCENDING;

    @Override
    public Set<Feature<? super @Nullable Void>> getImpliedFeatures() {
      return Collections.emptySet();
    }
  }

  /**

          .suppressing(parentBuilder.getSuppressedTests())
          .createTestSuite();
    }
  }

  @Override
  Set<Feature<?>> computeMultimapGetFeatures(Set<Feature<?>> multimapFeatures) {
    Set<Feature<?>> derivedFeatures = super.computeMultimapGetFeatures(multimapFeatures);
    if (derivedFeatures.contains(CollectionFeature.SUPPORTS_ADD)) {