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// 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
// 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() {}