LanguageFeatures/nnbd/weak/future_flattening_A01_t54.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 async function with `Future<FutureOr<Never>>`
/// return type can be `null` in the weak mode according to the Issue #44246,
/// etc. evaluation.
///
/// @Issue 41324, 41437, 44246
/// @Issue https://github.com/dart-lang/language/issues/1346
///
/// @author iarkh@unipro.ru

// Requirements=nnbd-weak

import "dart:async";
import "../../../Utils/expect.dart";

dynamic getNull() => null;

Future test() async {
  FutureOr<Never> i = await getNull();
  return i;
}

main() {
  asyncStart();
  test().then((value) { Expect.isNull(value); });
  asyncEnd();
}