LanguageFeatures/nnbd/weak/future_flattening_A01_t10.dart

/*
 * Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
 * for details. All rights reserved. Use of this source code is governed by a
 * BSD-style license that can be found in the LICENSE file.
 */
/**
 * @assertion The flatten function is modified as follows:
 *
 * [flatten(T)] is defined by cases on [T]:
 *
 *   if [T] is [S?] then [flatten(T) = flatten(S)?]
 *   otherwise if [T] is [S*] then [flatten(T) = flatten(S)*]
 *   otherwise if [T] is [FutureOr<S>] then [flatten(T) = S]
 *   otherwise [if T <: Future] then let [S] be a type such that [T <:
 *       Future<S>] and for all [R], if [T <: Future<R>] then [S <: R]; then
 *       [flatten(T) = S]
 *   otherwise [flatten(T) = T]
 *
 * @description Checks that type of await expression matches with the expected
 * non-nullable legacy types statically and the expression cannot be null.
 *
 * @description Check that type of `await` expression match with expected type
 * dynamically for the custom legacy class type parameter and the expression can
 * be `null` in weak mode.
 *
 * Here is a situation where sound and non-sound null checking produce different
 * results. The `null` value is tested using `null as A`, and such a cast
 * succeeds. So `test()` does not throw error  and returns `Future<A>` that will
 * be completed with `null`. No dynamic error here.
 *
 * @author iarkh@unipro.ru
 */
// Requirements=nnbd-weak

import "dart:async";
import "future_flattening_legacy_lib.dart";

Future<A> test() async {
  A a = await (null as A);
  return new Future<A>.value(new A());
}

main() {}