| // 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() {} |