Implement [Generator].prototype.return.

src/js/generator.js

 // Copyright 2013 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.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 19 matching lines @@
   if (!IS_GENERATOR(this)) {
     throw MakeTypeError(kIncompatibleMethodReceiver,
                         '[Generator].prototype.next', this);
   }
 
   var continuation = %GeneratorGetContinuation(this);
   if (continuation > 0) {
     // Generator is suspended.
     DEBUG_PREPARE_STEP_IN_IF_STEPPING(this);
     try {
-      return %_GeneratorNext(this, value);
+      let result = %_GeneratorNext(this, value);
+      if (result.done) %GeneratorClose(this);
+      return result;
     } catch (e) {
       %GeneratorClose(this);
       throw e;
     }
   } else if (continuation == 0) {
     // Generator is already closed.
-    return { value: void 0, done: true };
+    return %_CreateIterResultObject(UNDEFINED, true);
   } else {
     // Generator is running.
     throw MakeTypeError(kGeneratorRunning);
+  }
+}
+
+
+function GeneratorObjectReturn(value) {
+  if (!IS_GENERATOR(this)) {
+    throw MakeTypeError(kIncompatibleMethodReceiver,
+                        '[Generator].prototype.return', this);
+  }
+
+  var continuation = %GeneratorGetContinuation(this);
+  if (continuation > 0) {
+    // Generator is suspended.
+    DEBUG_PREPARE_STEP_IN_IF_STEPPING(this);
+    try {
+      let result = %_GeneratorReturn(this, value);
+      if (result.done) %GeneratorClose(this);
+      return result;
+    } catch (e) {
+      %GeneratorClose(this);
+      throw e;
+    }
+  } else if (continuation == 0) {
+    // Generator is already closed.
+    return %_CreateIterResultObject(value, true);
+  } else {
+    // Generator is running.
+    throw MakeTypeError(kGeneratorRunning);
   }
 }
 
 
 function GeneratorObjectThrow(exn) {
   if (!IS_GENERATOR(this)) {
     throw MakeTypeError(kIncompatibleMethodReceiver,
                         '[Generator].prototype.throw', this);
   }
 
   var continuation = %GeneratorGetContinuation(this);
   if (continuation > 0) {
     // Generator is suspended.
     try {
-      return %_GeneratorThrow(this, exn);
+      let result = %_GeneratorThrow(this, exn);
+      if (result.done) %GeneratorClose(this);
+      return result;
     } catch (e) {
       %GeneratorClose(this);
       throw e;
     }
   } else if (continuation == 0) {
     // Generator is already closed.
     throw exn;
   } else {
     // Generator is running.
     throw MakeTypeError(kGeneratorRunning);
   }
 }
 
 // ----------------------------------------------------------------------------
 
-// Both Runtime_GeneratorNext and Runtime_GeneratorThrow are supported by
-// neither Crankshaft nor TurboFan, disable optimization of wrappers here.
+// None of the three resume operations (Runtime_GeneratorNext,
+// Runtime_GeneratorReturn, Runtime_GeneratorThrow) is supported by
+// Crankshaft or TurboFan.  Disable optimization of wrappers here.
 %NeverOptimizeFunction(GeneratorObjectNext);
+%NeverOptimizeFunction(GeneratorObjectReturn);
 %NeverOptimizeFunction(GeneratorObjectThrow);
 
 // Set up non-enumerable functions on the generator prototype object.
 var GeneratorObjectPrototype = GeneratorFunctionPrototype.prototype;
 utils.InstallFunctions(GeneratorObjectPrototype,
                        DONT_ENUM,
                       ["next", GeneratorObjectNext,
+                       "return", GeneratorObjectReturn,
                        "throw", GeneratorObjectThrow]);
 
 %AddNamedProperty(GeneratorObjectPrototype, "constructor",
     GeneratorFunctionPrototype, DONT_ENUM | READ_ONLY);
 %AddNamedProperty(GeneratorObjectPrototype,
     toStringTagSymbol, "Generator", DONT_ENUM | READ_ONLY);
 %InternalSetPrototype(GeneratorFunctionPrototype, GlobalFunction.prototype);
 %AddNamedProperty(GeneratorFunctionPrototype,
     toStringTagSymbol, "GeneratorFunction", DONT_ENUM | READ_ONLY);
 %AddNamedProperty(GeneratorFunctionPrototype, "constructor",
     GeneratorFunction, DONT_ENUM | READ_ONLY);
 %InternalSetPrototype(GeneratorFunction, GlobalFunction);
 
 })