LanguageFeatures/Super-mixins/covariance_t07.dart

// Copyright (c) 2018, 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 In a mixin declaration like
/// mixin A<X extends S, Y extends T> on B, C implements D, E { body }
/// the on clause declares the interfaces B and C as super-class constraints of
/// the mixin. Having a super-class constaint allows the mixin declaration
/// instance members to perform super-invocations (like super.foo()) if they are
/// allowed by a class implementing both B and C. The mixin introduced by A can
/// then only be applied to classes that implement both B and C.
///
/// @description Checks that it is a runtime error if mixin is applied to the
/// class which doesn't implement required interface by covariant. See
/// https://github.com/dart-lang/sdk/issues/35111#issuecomment-437291038
/// @issue 35111
/// @author sgrekhov@unipro.ru

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

class S {}
class X extends S {}
class Y extends X {}

class A<T extends S> {
  bar(T n) {}
}

class B<T extends S> extends A<S> {
  bar(covariant T i) {}
}

mixin M<T extends S> on A<S> {
  test(T t) {
    super.bar(t);
  }
}

class MA extends B<Y> with M<X> {}

main() {
  Expect.throws(() {
    new MA().test(new Y());
  });
}