Runtime - Support frozen intrinsics (#411)

* Add failing test for runtime with frozen intrinsics
* Add runtime support for frozen intrinsics
* Add runtime support for frozen iterator prototypes

packages/regenerator-runtime/runtime.js

@@ -86,9 +86,9 @@ var runtime = (function (exports) {
   // This is a polyfill for %IteratorPrototype% for environments that
   // don't natively support it.
   var IteratorPrototype = {};
-  IteratorPrototype[iteratorSymbol] = function () {
+  define(IteratorPrototype, iteratorSymbol, function () {
     return this;
-  };
+  });
 
   var getProto = Object.getPrototypeOf;
   var NativeIteratorPrototype = getProto && getProto(getProto(values([])));
@@ -102,8 +102,9 @@ var runtime = (function (exports) {
 
   var Gp = GeneratorFunctionPrototype.prototype =
     Generator.prototype = Object.create(IteratorPrototype);
-  GeneratorFunction.prototype = Gp.constructor = GeneratorFunctionPrototype;
-  GeneratorFunctionPrototype.constructor = GeneratorFunction;
+  GeneratorFunction.prototype = GeneratorFunctionPrototype;
+  define(Gp, "constructor", GeneratorFunctionPrototype);
+  define(GeneratorFunctionPrototype, "constructor", GeneratorFunction);
   GeneratorFunction.displayName = define(
     GeneratorFunctionPrototype,
     toStringTagSymbol,
@@ -217,9 +218,9 @@ var runtime = (function (exports) {
   }
 
   defineIteratorMethods(AsyncIterator.prototype);
-  AsyncIterator.prototype[asyncIteratorSymbol] = function () {
+  define(AsyncIterator.prototype, asyncIteratorSymbol, function () {
     return this;
-  };
+  });
   exports.AsyncIterator = AsyncIterator;
 
   // Note that simple async functions are implemented on top of
@@ -412,13 +413,13 @@ var runtime = (function (exports) {
   // iterator prototype chain incorrectly implement this, causing the Generator
   // object to not be returned from this call. This ensures that doesn't happen.
   // See /~https://github.com/facebook/regenerator/issues/274 for more details.
-  Gp[iteratorSymbol] = function() {
+  define(Gp, iteratorSymbol, function() {
     return this;
-  };
+  });
 
-  Gp.toString = function() {
+  define(Gp, "toString", function() {
     return "[object Generator]";
-  };
+  });
 
   function pushTryEntry(locs) {
     var entry = { tryLoc: locs[0] };

test/frozen-intrinsics.js

@@ -0,0 +1,39 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+var assert = require("assert");
+
+var getPrototypeOf = Reflect.getPrototypeOf;
+function getConstructorOf(obj) {
+  return getPrototypeOf(obj).constructor;
+}
+
+var SymbolIterator = (typeof Symbol && Symbol.iterator) || '@@iterator';
+var ArrayIteratorObject = new Array()[SymbolIterator]();
+var ArrayIteratorPrototype = getPrototypeOf(ArrayIteratorObject);
+var IteratorPrototype = getPrototypeOf(ArrayIteratorPrototype);
+async function* AsyncGeneratorFunctionInstance() {}
+var AsyncGeneratorFunction = getConstructorOf(
+  AsyncGeneratorFunctionInstance,
+);
+var AsyncGenerator = AsyncGeneratorFunction.prototype;
+var AsyncGeneratorPrototype = AsyncGenerator.prototype;
+var AsyncIteratorPrototype = getPrototypeOf(AsyncGeneratorPrototype);
+
+// freeze relevant intrinsics
+Object.freeze(Object.prototype);
+Object.freeze(IteratorPrototype);
+Object.freeze(ArrayIteratorPrototype);
+Object.freeze(AsyncGenerator);
+Object.freeze(AsyncGeneratorPrototype);
+Object.freeze(AsyncIteratorPrototype);
+
+describe("Frozen intrinsics test", function () {
+  it("regenerator-runtime doesn't fail to initialize when Object prototype is frozen", function() {
+    require("./runtime.js");
+  });
+});

test/run.js

@@ -141,6 +141,12 @@ if (semver.gte(process.version, "4.0.0")) {
   ]);
 }
 
+enqueue("mocha", [
+  "--harmony",
+  "--reporter", "spec",
+  "./test/frozen-intrinsics.js",
+]);
+
 enqueue(convert, [
   "./test/tests.es6.js",
   "./test/tests.es5.js"