* we're copying into a `contents` array whose type allows it to contain nulls. Still, it's
       * worth noting that we promise not to put nulls into the array in the first `size` elements.
       * We uphold that promise here because our callers promise that `elements` will not contain
       * nulls in its first `n` elements.
       */
      System.arraycopy(elements, 0, contents, size, n);
      size += n;

       * we're copying into a `contents` array whose type allows it to contain nulls. Still, it's
       * worth noting that we promise not to put nulls into the array in the first `size` elements.
       * We uphold that promise here because our callers promise that `elements` will not contain
       * nulls in its first `n` elements.
       */
      System.arraycopy(elements, 0, contents, size, n);
      size += n;

  }

  @JsFunction
  interface IThenOnRejectedCallbackFn<V extends @Nullable Object> {
    V onInvoke(Object p0);
  }
}

/** Subset of the elemental2 Promise API. */
@JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Promise")
class Promise<T extends @Nullable Object> implements IThenable<T> {

  @JsFunction
  interface PromiseExecutorCallbackFn<T extends @Nullable Object> {
    @JsFunction

  }

  public void testPowerSetIteration_manual() {
    ImmutableSet<Integer> elements = ImmutableSet.of(1, 2, 3);
    Set<Set<Integer>> powerSet = powerSet(elements);
    // The API doesn't promise this iteration order, but it's convenient here.
    Iterator<Set<Integer>> i = powerSet.iterator();
    assertEquals(ImmutableSet.of(), i.next());
    assertEquals(ImmutableSet.of(1), i.next());

            // callable actually completes. (We could detect completion in our wrapper
            // `AsyncCallable task`.) However, our contract also promises:
            //
            // 2. not to cancel any Future the user returned from an AsyncCallable
            //
            // We promise this because, once we cancel that Future, we would no longer be able to

  `One, indeed!' said the Dormouse indignantly.  However, he
consented to go on.  `And so these three little sisters--they
were learning to draw, you know--'

  `What did they draw?' said Alice, quite forgetting her promise.

  `Treacle,' said the Dormouse, without considering at all this
time.

  `I want a clean cup,' interrupted the Hatter:  `let's all move
one place on.'

 * iterator generator may delegate the work of creating the underlying collection to an inner
 * collection generator.
 *
 * <p>{@code GwtTestSuiteGenerator} expects every {@code DerivedIterator} implementation to provide
 * a one-arg constructor accepting its inner generator as an argument. This requirement enables it
 * to generate source code (since GWT cannot use reflection to generate the suites).
 *
 * @author Chris Povirk
 */

import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible
@Retention(RUNTIME)
@Target(TYPE)
@TypeQualifierDefault({FIELD, METHOD, PARAMETER})
@Nonnull

import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible
@Retention(RUNTIME)
@Target(TYPE)
@TypeQualifierDefault({FIELD, METHOD, PARAMETER})
@Nonnull

import javax.annotation.meta.TypeQualifierDefault;

/**
 * Marks all "top-level" types as non-null in a way that is recognized by Kotlin. Note that this
 * unfortunately includes type-variable usages, so we also provide {@link ParametricNullness} to
 * "undo" it as best we can.
 */
@GwtCompatible
@Retention(RUNTIME)
@Target(TYPE)
@TypeQualifierDefault({FIELD, METHOD, PARAMETER})
@Nonnull