tests/language/mixin_declaration/mixin_declaration_invalid_override_test.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.

import "package:expect/expect.dart";

// Test various invalid super-constraints for mixin declarations.

abstract class UnaryNum {
  num foo(num x);
}

// Overrides must still be valid, wrt. signatures and types.

mixin M3 on UnaryNum {
  // M3.foo is a valid override of UnaryNum.foo
  num foo(num x) => super.foo(x) * 2;
}

// Invalid signature override (overriding optional parameter with required).
class C3 implements UnaryNum {
  // C3.foo is a valid override of UnaryNum.foo
  num foo([num x = 17]) => x;
}

// M3.foo is not a valid override for C3.foo.
class A3 extends C3 with M3 {}
//    ^
// [cfe] Applying the mixin 'M3' to 'C3' introduces an erroneous override of 'foo'.
//                       ^^
// [analyzer] COMPILE_TIME_ERROR.INVALID_OVERRIDE

// Invalid type override (overriding `int` return with `num` return).
class C4 implements UnaryNum {
  // C4.foo is a valid override of UnaryNum.foo
  int foo(num x) => x.toInt();
}

// M3.foo is not a valid override for C4.foo.
class A4 extends C4 with M3 {}
//    ^
// [cfe] Applying the mixin 'M3' to 'C4' introduces an erroneous override of 'foo'.
//                       ^^
// [analyzer] COMPILE_TIME_ERROR.INVALID_OVERRIDE

// It's not required to have an implementation of members which are not super-
// invoked, if the application class is abstract.
abstract class C5 {
  num foo(num x);
  num bar(num x);
}

mixin M5 on C5 {
  num baz(num x) => super.foo(x);
}

abstract class C5Foo implements C5 {
  num foo(num x) => x;
}

abstract mixin class C5Bar implements C5 {
  num bar(num x) => x;
}

// Valid abstract class, super-invocation of foo hits implementation,
// even if bar is still abstract.
abstract class A5Foo = C5Foo with M5;
// Invalid since super-invocation of foo does not hit concrete implementation.
abstract class _ = C5Bar with M5;
//                            ^^
// [analyzer] COMPILE_TIME_ERROR.MIXIN_APPLICATION_NO_CONCRETE_SUPER_INVOKED_MEMBER
// [cfe] The class doesn't have a concrete implementation of the super-invoked member 'foo'.

class A5FooConcrete = A5Foo with C5Bar;

main() {
  Expect.equals(42, A5FooConcrete().baz(42));
}