Migrate language_2/return to NNBD.

Change-Id: I3666b69e8371330e2e615aef9fcdecbb1d0753b9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/150471
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>

tests/language/return/in_loop_test.dart

@@ -0,0 +1,25 @@
+// Copyright (c) 2012, 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.
+// Test for a dart2js bug where the live environment was not computed
+// right.
+
+import "package:expect/expect.dart";
+
+class A {
+  foo() {
+    var x = 0;
+    while (true) {
+      if (true) {
+        return 42;
+      } else {}
+      x = bar();
+    }
+  }
+
+  bar() => 1;
+}
+
+main() {
+  Expect.equals(42, new A().foo());
+}

tests/language/return/skip_expression_test.dart

@@ -0,0 +1,34 @@
+// Copyright (c) 2012, 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";
+
+class OneArg<A> {
+  OneArg<A> get foo => new OneArg<A>();
+  OneArg<A> get bar {
+    return new OneArg<A>();
+  }
+}
+
+class TwoArgs<A, B> {
+  TwoArgs<A, B> get foo => new TwoArgs<A, B>();
+  TwoArgs<A, B> get bar {
+    return new TwoArgs<A, B>();
+  }
+}
+
+void main() {
+  Expect.isTrue(new OneArg<String>().foo is OneArg);
+  Expect.isTrue(new OneArg<String>().bar is OneArg);
+  Expect.isTrue(new TwoArgs<String, int>().foo is TwoArgs);
+  Expect.isTrue(new TwoArgs<String, int>().bar is TwoArgs);
+
+  // TODO(karlklose): Please remove the return when dart2js can handle
+  // the type tests after it.
+  return;
+  Expect.isTrue(new OneArg<String>().foo is OneArg<String>);
+  Expect.isTrue(new OneArg<String>().bar is OneArg<String>);
+  Expect.isTrue(new TwoArgs<String, int>().foo is TwoArgs<String, int>);
+  Expect.isTrue(new TwoArgs<String, int>().bar is TwoArgs<String, int>);
+}

tests/language/return/this_type_test.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2013, 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 the engine does not infer the wrong type for [:A.foo:].
+
+import "package:expect/expect.dart";
+
+class A {
+  foo() => this;
+}
+
+class B extends A {}
+
+main() {
+  Expect.isTrue(new B().foo() is B);
+}

tests/language/return/type_test.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2012, 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";
+
+int returnString1() => 's';  /*@compile-error=unspecified*/
+void returnNull() => null;
+void returnString2() => 's';  /*@compile-error=unspecified*/
+
+main() {
+  returnString1();
+  returnNull();
+  returnString2();
+}