[tests] Language tests for 'base' class modifier.

Change-Id: I2b5cf3d2d367d0cfd2d2da60268b36f16225ab1d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/276762
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Kallen Tu <kallentu@google.com>

tests/language/class_modifiers/base/base_class_abstract_construct_error_test.dart

@@ -0,0 +1,23 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Error when attempting to construct an abstract base class.
+
+abstract base class NotConstructable {}
+
+mixin M {}
+abstract base class AlsoNotConstructable = Object with M;
+
+main() {
+  var error = NotConstructable();
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  var error2 = AlsoNotConstructable();
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}

tests/language/class_modifiers/base/base_class_base_subtype_test.dart

@@ -0,0 +1,37 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow subtypes of a base class or mixin to be base as well.
+
+import 'package:expect/expect.dart';
+
+base class BaseClass {
+  int foo = 0;
+}
+base class A extends BaseClass {}
+base class B implements BaseClass {
+  @override
+  int foo = 1;
+}
+
+base mixin BaseMixin {
+  int foo = 0;
+}
+base class AMixin with BaseMixin {}
+base class BMixin = Object with BaseMixin;
+
+// Used for trivial runtime tests of the base subtypes.
+class AConcrete extends A {}
+class BConcrete extends B {}
+class AMixinConcrete extends AMixin {}
+class BMixinConcrete extends BMixin {}
+
+main() {
+  Expect.equals(0, AConcrete().foo);
+  Expect.equals(1, BConcrete().foo);
+  Expect.equals(0, AMixinConcrete().foo);
+  Expect.equals(0, BMixinConcrete().foo);
+}

tests/language/class_modifiers/base/base_class_extend_lib.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base classes to be extended by multiple classes in the same library.
+
+base class BaseClass {
+  int foo = 0;
+}
+
+abstract class A extends BaseClass {}
+
+class B extends BaseClass {}

tests/language/class_modifiers/base/base_class_extend_not_base_final_error_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Error when extending a base class where the subclass is not also a base class
+// or final.
+
+import 'base_class_extend_lib.dart';
+
+abstract class AOutside extends BaseClass {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+class BOutside extends BaseClass {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified

tests/language/class_modifiers/base/base_class_extend_outside_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base classes to be extended by multiple classes outside its library.
+
+import 'package:expect/expect.dart';
+import 'base_class_extend_lib.dart';
+
+abstract base class AOutside extends BaseClass {}
+
+base class AOutsideImpl extends AOutside {}
+
+base class BOutside extends BaseClass {}
+
+main() {
+  Expect.equals(0, AOutsideImpl().foo);
+  Expect.equals(0, BOutside().foo);
+}

tests/language/class_modifiers/base/base_class_extend_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base classes to be extended by multiple classes inside its
+// library.
+
+import 'package:expect/expect.dart';
+import 'base_class_extend_lib.dart';
+
+class AImpl extends A {}
+
+main() {
+  Expect.equals(0, AImpl().foo);
+  Expect.equals(0, B().foo);
+}

tests/language/class_modifiers/base/base_class_implement_error_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Error when attempting to implement base class outside of library.
+
+import 'base_class_implement_lib.dart';
+
+abstract class AOutside implements BaseClass {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+class BOutside implements BaseClass {
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_class_implement_lib.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base classes to be implemented by multiple classes in the same library.
+
+base class BaseClass {
+  int foo = 0;
+}
+
+abstract class A implements BaseClass {}
+
+class B implements BaseClass {
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_class_implement_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base classes to be implemented by multiple classes inside its
+// library.
+
+import 'package:expect/expect.dart';
+import 'base_class_implement_lib.dart';
+
+class AImpl implements A {
+  @override
+  int foo = 1;
+}
+
+main() {
+  Expect.equals(1, AImpl().foo);
+  Expect.equals(1, B().foo);
+}

tests/language/class_modifiers/base/base_class_mixin_on_lib.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+base class BaseClass {}
+
+abstract class A extends BaseClass {}
+
+class B extends BaseClass {}
+
+base mixin BaseMixin {}
+
+class C extends BaseClass with BaseMixin {}
+
+class D with BaseMixin {}

tests/language/class_modifiers/base/base_class_mixin_on_test.dart

@@ -0,0 +1,36 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow a base type to appear in the "on" clause of a mixin declaration in
+// another library.
+
+import 'package:expect/expect.dart';
+import 'base_class_mixin_on_lib.dart';
+
+mixin MA on BaseClass {}
+mixin MB on BaseClass {}
+
+class ConcreteA extends A with MA, MB {
+  int foo = 0;
+}
+
+mixin MC on BaseClass, BaseMixin {}
+
+class ConcreteC extends C with MC {
+  int foo = 0;
+}
+
+mixin MCSingular on BaseMixin {}
+
+class ConcreteD extends D with MCSingular {
+  int foo = 0;
+}
+
+main() {
+  Expect.equals(0, ConcreteA().foo);
+  Expect.equals(0, ConcreteC().foo);
+  Expect.equals(0, ConcreteD().foo);
+}

tests/language/class_modifiers/base/base_class_part_lib.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+part of 'base_class_part_test.dart';
+
+class A extends BaseClass {}
+
+class B implements BaseClass {
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_class_part_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow extending and implementing base classes in a part file of
+// the same library
+
+import 'package:expect/expect.dart';
+part 'base_class_part_lib.dart';
+
+base class BaseClass {
+  int foo = 0;
+}
+
+main() {
+  Expect.equals(0, A().foo);
+  Expect.equals(1, B().foo);
+}

tests/language/class_modifiers/base/base_class_syntax_disabled_error_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2022, 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.
+
+// Make sure errors are emitted when trying to use base classes without
+// the `class-modifiers` experiment enabled.
+
+base class BaseClass {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+mixin M {}
+base class BaseClassTypeAlias = Object with M;
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+base mixin BaseMixin {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified

tests/language/class_modifiers/base/base_class_syntax_error_test.dart

@@ -0,0 +1,45 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Syntax errors such as using `base` keyword in a place other than a class or
+// mixin.
+
+abstract class BaseMembers {
+  base int foo;
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  int bar(base int x);
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  base void bar2();
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+base base class BaseDuplicateClass {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+base abstract class BaseAbstractClass {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+class BaseVariable {
+  int foo() {
+    base var x = 2;
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+    return x;
+  }
+}

tests/language/class_modifiers/base/base_class_syntax_mixin_class_test.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Tests that we can still use `base` as an identifier for mixin names.
+
+import 'package:expect/expect.dart';
+
+mixin class base {
+  int x = 0;
+}
+
+main() {
+  Expect.equals(0, base().x);
+}

tests/language/class_modifiers/base/base_class_syntax_mixin_test.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Tests that we can still use `base` as an identifier for mixin names.
+
+import 'package:expect/expect.dart';
+
+mixin base {
+  int x = 0;
+}
+
+class Class with base {}
+
+main() {
+  Expect.equals(0, Class().x);
+}

tests/language/class_modifiers/base/base_class_syntax_test.dart

@@ -0,0 +1,58 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Tests we can still use `base` as an identifier.
+
+import 'package:expect/expect.dart';
+
+class base {
+  int x = 0;
+}
+
+class BaseField {
+  int base = 0;
+}
+
+class BaseMethod {
+  int base() => 1;
+  int foo(int base) => base;
+  int? foo1([int? base]) => base;
+  int? foo2({int? base}) => base;
+}
+
+class BaseVariable {
+  int foo() {
+    var base = 2;
+    return base;
+  }
+}
+
+class BaseAsType {
+  int foo(base x) => x.x;
+  base foo1 = base();
+}
+
+main() {
+  var baseClass = base();
+  var baseField = BaseField();
+  var baseMethod = BaseMethod();
+  var baseVariable = BaseVariable();
+  var baseAsType = BaseAsType();
+
+  Expect.equals(0, baseClass.x);
+
+  Expect.equals(0, baseField.base);
+
+  Expect.equals(1, baseMethod.base());
+  Expect.equals(1, baseMethod.foo(1));
+  Expect.equals(1, baseMethod.foo1(1));
+  Expect.equals(1, baseMethod.foo2(base: 1));
+
+  Expect.equals(2, baseVariable.foo());
+
+  Expect.equals(0, baseAsType.foo(base()));
+  Expect.equals(0, baseAsType.foo1.x);
+}

tests/language/class_modifiers/base/base_class_typedef_implement_error_test.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Error when attempting to implement typedef base class outside of its library.
+
+import 'base_class_typedef_lib.dart';
+
+class BTypeDef implements BaseClassTypeDef {
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_class_typedef_lib.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+base class BaseClass {
+  int foo = 0;
+}
+
+typedef BaseClassTypeDef = BaseClass;
+
+class A extends BaseClassTypeDef {}
+
+class B implements BaseClassTypeDef {
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_class_typedef_outside_of_library_lib.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+import 'base_class_typedef_outside_of_library_lib2.dart';
+
+base class BaseClass {
+  int foo = 0;
+}
+
+class A extends ATypeDef {}
+
+class B implements ATypeDef {
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_class_typedef_outside_of_library_lib2.dart

@@ -0,0 +1,9 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+import "base_class_typedef_outside_of_library_lib.dart";
+
+typedef ATypeDef = BaseClass;

tests/language/class_modifiers/base/base_class_typedef_outside_of_library_test.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow typedef in different library, used by class in library.
+
+import 'package:expect/expect.dart';
+import 'base_class_typedef_outside_of_library_lib.dart';
+
+main() {
+  Expect.equals(0, A().foo);
+  Expect.equals(1, B().foo);
+}

tests/language/class_modifiers/base/base_class_typedef_test.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow typedef base classes to be extended and implemented by
+// multiple classes in the same library.
+
+import 'package:expect/expect.dart';
+import 'base_class_typedef_lib.dart';
+
+main() {
+  Expect.equals(0, A().foo);
+  Expect.equals(1, B().foo);
+}

tests/language/class_modifiers/base/base_class_typedef_used_outside_error_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Error when trying to implement a typedef base class outside of
+// the base class' library when the typedef is also outside the base class
+// library.
+
+import 'base_class_typedef_used_outside_lib.dart';
+
+typedef ATypeDef = BaseClass;
+
+class B implements ATypeDef {
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_class_typedef_used_outside_lib.dart

@@ -0,0 +1,9 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+base class BaseClass {
+  int foo = 0;
+}

tests/language/class_modifiers/base/base_mixin_implement_error_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Error when attempting to implement base mixin outside of library.
+
+import 'base_mixin_implement_lib.dart';
+
+abstract class AOutside implements BaseMixin {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+class BOutside implements BaseMixin {
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_mixin_implement_lib.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base mixins to be implemented by multiple classes in the same library.
+
+base mixin BaseMixin {
+  int foo = 0;
+}
+
+abstract class A implements BaseMixin {}
+
+class B implements BaseMixin {
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_mixin_typedef_with_lib.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+base mixin BaseMixin {
+  int foo = 0;
+}
+
+typedef BaseMixinTypeDef = BaseMixin;
+
+class A with BaseMixinTypeDef {
+  @override
+  int foo = 1;
+}

tests/language/class_modifiers/base/base_mixin_typedef_with_outside_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow typedef base mixins to be mixed in by multiple classes outside the
+// library.
+
+import 'package:expect/expect.dart';
+import 'base_mixin_typedef_with_lib.dart';
+
+abstract base class AOutside with BaseMixinTypeDef {}
+
+class AOutsideImpl extends AOutside {}
+
+base class BOutside with BaseMixinTypeDef {}
+
+main() {
+  Expect.equals(0, AOutsideImpl().foo);
+  Expect.equals(0, BOutside().foo);
+}

tests/language/class_modifiers/base/base_mixin_typedef_with_test.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow typedef base mixins to be mixed in by multiple classes in the same
+// library.
+
+import 'package:expect/expect.dart';
+import 'base_mixin_typedef_with_lib.dart';
+
+main() {
+  Expect.equals(1, A().foo);
+}

tests/language/class_modifiers/base/base_mixin_with_lib.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base mixins to be mixed by multiple classes in the same library.
+
+base mixin BaseMixin {
+  int foo = 0;
+}
+
+abstract class A with BaseMixin {}
+
+class B with BaseMixin {}

tests/language/class_modifiers/base/base_mixin_with_not_base_final_error_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Error when mixing in a base mixin where the class mixing it in is not base or
+// final.
+
+import 'base_mixin_with_lib.dart';
+
+abstract class AOutside with BaseMixin {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+class BOutside with BaseMixin {}
+// ^
+// [analyzer] unspecified
+// [cfe] unspecified

tests/language/class_modifiers/base/base_mixin_with_outside_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base mixins to be mixed by multiple classes outside its library.
+
+import 'package:expect/expect.dart';
+import 'base_mixin_with_lib.dart';
+
+abstract base class AOutside with BaseMixin {}
+
+class AOutsideImpl extends AOutside {}
+
+base class BOutside with BaseMixin {}
+
+main() {
+  Expect.equals(0, AOutsideImpl().foo);
+  Expect.equals(0, BOutside().foo);
+}

tests/language/class_modifiers/base/base_mixin_with_test.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=class-modifiers
+
+// Allow base mixins to be mixed by multiple classes in the same library.
+
+import 'package:expect/expect.dart';
+import 'base_mixin_with_lib.dart';
+
+class AImpl extends A {}
+
+main() {
+  Expect.equals(0, AImpl().foo);
+  Expect.equals(0, B().foo);
+}