[es6] Re-implement rest parameters via desugaring.

test/mjsunit/harmony/rest-params.js

 // Copyright 2014 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-rest-parameters
 
 (function testRestIndex() {
   assertEquals(5, (function(...args) { return args.length; })(1,2,3,4,5));
   assertEquals(4, (function(a, ...args) { return args.length; })(1,2,3,4,5));
   assertEquals(3, (function(a, b, ...args) { return args.length; })(1,2,3,4,5));
   assertEquals(2, (function(a, b, c, ...args) {
                       return args.length; })(1,2,3,4,5));
   assertEquals(1, (function(a, b, c, d, ...args) {
                       return args.length; })(1,2,3,4,5));
   assertEquals(0, (function(a, b, c, d, e, ...args) {
                     return args.length; })(1,2,3,4,5));
 })();
 
+
 var strictTest = (function() {
   "use strict";
   return function strictTest(a, b, ...c) {
     assertEquals(Array, c.constructor);
     assertTrue(Array.isArray(c));
 
     var expectedLength = arguments.length >= 3 ? arguments.length - 2 : 0;
     assertEquals(expectedLength, c.length);
 
     for (var i = 2, j = 0; i < arguments.length; ++i) {
       assertEquals(c[j++], arguments[i]);
     }
   };
 })();
 
+
 function sloppyTest(a, b, ...c) {
   assertEquals(Array, c.constructor);
   assertTrue(Array.isArray(c));
 
   var expectedLength = arguments.length >= 3 ? arguments.length - 2 : 0;
   assertEquals(expectedLength, c.length);
 
   for (var i = 2, j = 0; i < arguments.length; ++i) {
     assertEquals(c[j++], arguments[i]);
   }
@@ skipping 118 matching lines @@
   function sloppyF(a, ...rest) {
     arguments[0] = 1;
     assertEquals(3, a);
     arguments[1] = 2;
     assertArrayEquals([4, 5], rest);
   }
   sloppyF(3, 4, 5);
 })();
 
 
-/* TODO(caitp): support arrow functions (blocked on spread operator support)
-(function testRestParamsArrowFunctions() {
-  "use strict";
-
-  var fn = (a, b, ...c) => c;
-  assertEquals([], fn());
-  assertEquals([], fn(1, 2));
-  assertEquals([3], fn(1, 2, 3));
-  assertEquals([3, 4], fn(1, 2, 3, 4));
-  assertEquals([3, 4, 5], fn(1, 2, 3, 4, 5));
-  assertThrows("var x = ...y => y;", SyntaxError);
-  assertEquals([], ((...args) => args)());
-  assertEquals([1,2,3], ((...args) => args)(1,2,3));
-})();*/
-
-
 (function testRestParamsWithNewTarget() {
   "use strict";
   class Base {
     constructor(...a) {
       this.base = a;
       assertEquals(arguments.length, a.length);
       var args = [];
       for (var i = 0; i < arguments.length; ++i) {
         args.push(arguments[i]);
       }
@@ skipping 28 matching lines @@
     function(){ eval("(class{foo(...rest) {'use strict';}});") }, SyntaxError);
 
   assertThrows(
     function(){ eval("function(a, ...rest){'use strict';}") }, SyntaxError);
   assertThrows(
     function(){ eval("(a, ...rest) => {'use strict';}") }, SyntaxError);
   assertThrows(
     function(){ eval("(class{foo(a, ...rest) {'use strict';}});") },
     SyntaxError);
 })();