Add sample language tests for valueClass feature

Add experimental_flag protection

Change-Id: I0dc83fd544beb58dce5631a2a80d4d9321e866ca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/155607
Commit-Queue: Javier López-Contreras <[email protected]>
Reviewed-by: Erik Ernst <[email protected]>

Author: javierlcontreras

tests/language/language.status

@@ -7,6 +7,7 @@ switch/case_warn_test: Skip # Analyzer only, see language_analyzer2.status
 
 [ $compiler != fasta ]
 nonfunction_type_aliases/*: Skip # github.com/dart-lang/language/issues/115
+value_class/*: Skip # Internship, jlcontreras
 
 [ $compiler == none ]
 invalid_returns/*: Skip # https://github.com/dart-lang/sdk/issues/34013

tests/language/value_class/creates_constructor_test.dart

@@ -0,0 +1,16 @@
+// 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.
+
+// A value class will automatically create an empty constructor if there is none yet
+
+const String valueClass = "valueClass";
+
+@valueClass
+class Animal {
+  final int numberOfLegs;
+}
+
+main() {
+  var cat = Animal(numberOfLegs: 4);
+}

tests/language/value_class/creates_equals_test.dart

@@ -0,0 +1,25 @@
+// 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.
+
+// Equals operator == by value should be implicitly created
+
+import 'package:expect/expect.dart';
+
+// A value class will automatically create an == operator if there is none yet
+
+const String valueClass = "valueClass";
+
+@valueClass
+class Animal {
+  final int numberOfLegs;
+}
+
+main() {
+  var cat = Animal(numberOfLegs: 4);
+  var dog = Animal(numberOfLegs: 4);
+  var human = Animal(numberOfLegs: 2);
+
+  Expect.equals(true, cat == dog);
+  Expect.equals(false, cat == human);
+}

tests/language/value_class/has_non_final_field_error_test.dart

@@ -0,0 +1,14 @@
+// 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.
+
+// It is a compile-time error if a value class has a non-final instance variable.
+
+const String valueClass = "valueClass";
+
+@valueClass
+class Animal {
+  int numberOfLegs;
+  //^
+  // [cfe] unspecified
+}

tests/language/value_class/inherits_non_value_class_error_test.dart

@@ -0,0 +1,14 @@
+// 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.
+
+// Value classes are always leaves in the tree of types
+
+const String valueClass = "valueClass";
+
+@valueClass
+class Animal {}
+
+class Cat implements Animal {}
+//                   ^^^^^^
+// [cfe] unspecified