* order of those futures, test that various get calls (timed before future completion, untimed
   * before future completion, and untimed after future completion) return or throw the proper
   * values.
   */
  @J2ktIncompatible
  @GwtIncompatible // used only in GwtIncompatible tests
  private static void runExtensiveMergerTest(Merger merger) throws InterruptedException {

   * order of those futures, test that various get calls (timed before future completion, untimed
   * before future completion, and untimed after future completion) return or throw the proper
   * values.
   */
  @J2ktIncompatible
  @GwtIncompatible // used only in GwtIncompatible tests
  private static void runExtensiveMergerTest(Merger merger) throws InterruptedException {

      Class<X> exceptionType, ClosingFunction<? super X, ? extends V> fallback, Executor executor) {
    return catchingMoreGeneric(exceptionType, fallback, executor);
  }

  // Avoids generic type capture inconsistency problems where |? extends V| is incompatible with V.
  private <X extends Throwable, W extends V> ClosingFuture<V> catchingMoreGeneric(
      Class<X> exceptionType, final ClosingFunction<? super X, W> fallback, Executor executor) {

       * `Enumeration<?>`, probably because of one of the following two bugs (and maybe those two
       * bugs are themselves just symptoms of the same underlying problem):
       *
       * https://github.com/typetools/checker-framework/issues/3030
       *
       * https://github.com/typetools/checker-framework/issues/3236
       */