LanguageFeatures/nnbd/weak/overriding/override_checking_A06_t001.dart

/*
 * Copyright (c) 2021, 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 If a class [C] in an opted-in library implements the same generic
 * class [I] more than once as [I0], .., [In], and at least one of the [Ii] is
 * not syntactically equal to the others, then it is an error if
 * [NNBD_TOP_MERGE(S0, ..., Sn)] is not defined where [Si] is [NORM(Ii)].
 * Otherwise, for the purposes of runtime subtyping checks, [C] is considered to
 * implement the canonical interface given by [NNBD_TOP_MERGE(S0, ..., Sn)].
 *
 * @description Check that that the result of NNBD_TOP_MERGE(Object, Object)] is
 * [Object] in weak mode.
 *
 * Dynamic type checks with unsound null checking erases `?` from types and add
 * `*` (recursively, so `List<int?>?` becomes `List<int*>*`). In particular
 * `LEGACY_SUBTYPE(Object Function(Object), Object? Function(Object?))` is true.
 *
 * @author iarkh@unipro.ru
 */
// Requirements=nnbd-weak

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

class B extends CHECK_TOP_MERGE<Object> {}
class C extends CHECK_TOP_MERGE<Object> {}

class D extends B implements C {}

void main() {
  Expect.isTrue(D().f is Object Function(Object));
  Expect.isTrue(D().f is Object? Function(Object?));
}