removeIfEmpty();
      }
      return changed;
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      checkNotNull(c);
      int oldSize = size(); // calls refreshIfEmpty
      boolean changed = delegate.retainAll(c);
      if (changed) {
        int newSize = delegate.size();
        totalSize += newSize - oldSize;
        removeIfEmpty();
      }

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

    addImpliedFeatures(sizesToTest);
    sizesToTest.retainAll(asList(CollectionSize.ZERO, CollectionSize.ONE, CollectionSize.SEVERAL));

    logger.fine("   Sizes: " + formatFeatureSet(sizesToTest));

        removeIfEmpty();
      }
      return changed;
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      checkNotNull(c);
      int oldSize = size(); // calls refreshIfEmpty
      boolean changed = delegate.retainAll(c);
      if (changed) {
        int newSize = delegate.size();
        totalSize += newSize - oldSize;
        removeIfEmpty();
      }

        unreleasedIndexCompatible.retainAll(getUnreleased());
        return unmodifiableList(unreleasedIndexCompatible);
    }

    public List<Version> getUnreleasedWireCompatible() {
        List<Version> unreleasedWireCompatible = new ArrayList<>(getWireCompatible());
        unreleasedWireCompatible.retainAll(getUnreleased());
        return unmodifiableList(unreleasedWireCompatible);
    }

  }

  public void testRetainAll_collection() {
    List<String> list = newArrayList("a", "b", "c", "d", "e");
    assertTrue(Iterables.retainAll(list, newArrayList("b", "d", "f")));
    assertEquals(newArrayList("b", "d"), list);
    assertFalse(Iterables.retainAll(list, newArrayList("b", "e", "d")));
    assertEquals(newArrayList("b", "d"), list);
  }

  public void testRetainAll_iterable() {

   */
  @Deprecated
  public static <T> Set<T> intersection(Set<? extends T> set1, Set<? extends T> set2) {
    Set<T> result = copyToSet(set1);
    result.retainAll(set2);
    return result;
  }

  private FeatureUtil() {}

    }
    if (intersect(features, requirements.getAbsentFeatures())) {
      if (logger.isLoggable(FINER)) {
        Set<Feature<?>> unwantedFeatures = copyToSet(requirements.getAbsentFeatures());
        unwantedFeatures.retainAll(features);
        logger.finer(
            Platform.format(
                "%s: skipping because these features are present: %s", method, unwantedFeatures));
      }
      return false;
    }

   */
  @Deprecated
  public static <T> Set<T> intersection(Set<? extends T> set1, Set<? extends T> set2) {
    Set<T> result = copyToSet(set1);
    result.retainAll(set2);
    return result;
  }

  private FeatureUtil() {}

    }
    if (intersect(features, requirements.getAbsentFeatures())) {
      if (logger.isLoggable(FINER)) {
        Set<Feature<?>> unwantedFeatures = copyToSet(requirements.getAbsentFeatures());
        unwantedFeatures.retainAll(features);
        logger.finer(
            Platform.format(
                "%s: skipping because these features are present: %s", method, unwantedFeatures));
      }
      return false;
    }

   * @param elementsToRetain the elements to retain
   * @return {@code true} if any element was removed from {@code iterator}
   */
  @CanIgnoreReturnValue
  public static boolean retainAll(Iterator<?> removeFrom, Collection<?> elementsToRetain) {
    checkNotNull(elementsToRetain);
    boolean result = false;
    while (removeFrom.hasNext()) {
      if (!elementsToRetain.contains(removeFrom.next())) {