[generators] Implement Generator.prototype.return.

test/mjsunit/harmony/function-sent.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --harmony-function-sent
 
 
 {
   function* g() { return function.sent }
   assertEquals({value: 42, done: true}, g().next(42));
 }
 
 
 {
   function* g() {
     try {
       yield function.sent;
     } finally {
       yield function.sent;
       return function.sent;
     }
   }
 
   {
-    x = g();
+    let x = g();
     assertEquals({value: 1, done: false}, x.next(1));
     assertEquals({value: 2, done: false}, x.next(2));
     assertEquals({value: 3, done: true}, x.next(3));
   }
 
   {
-    x = g();
+    let x = g();
     assertEquals({value: 1, done: false}, x.next(1));
     assertEquals({value: 2, done: false}, x.throw(2));
     assertEquals({value: 3, done: true}, x.next(3));
   }
+
+  {
+    let x = g();
+    assertEquals({value: 1, done: false}, x.next(1));
+    assertEquals({value: 2, done: false}, x.return(2));
+    assertEquals({value: 3, done: true}, x.next(3));
+  }
 }
 
 
 {
   function* inner() {
     try {
       yield function.sent;
     } finally {
       return 666;
     }
   }
 
   function* g() {
     yield function.sent;
     yield* inner();
     return function.sent;
   }
 
   {
-    x = g();
+    let x = g();
     assertEquals({value: 1, done: false}, x.next(1));
     assertEquals({value: undefined, done: false}, x.next(2));
     assertEquals({value: 3, done: true}, x.next(3));
   }
 
   {
-    x = g();
+    let x = g();
     assertEquals({value: 1, done: false}, x.next(1));
     assertEquals({value: undefined, done: false}, x.next(2));
     assertEquals({value: 42, done: true}, x.throw(42));
   }
+
+  {
+    let x = g();
+    assertEquals({value: 1, done: false}, x.next(1));
+    assertEquals({value: undefined, done: false}, x.next(2));
+    assertEquals({value: 42, done: true}, x.return(42));
+  }
 }
 
 
 assertThrows("function f() { return function.sent }", SyntaxError);
 assertThrows("() => { return function.sent }", SyntaxError);
 assertThrows("() => { function.sent }", SyntaxError);
 assertThrows("() => function.sent", SyntaxError);
 assertThrows("({*f() { function.sent }})", SyntaxError);
 assertDoesNotThrow("({*f() { return function.sent }})");