[es6] Fix scoping for default parameters in arrow functions

test/mjsunit/harmony/regress/regress-4395.js

+// Copyright 2015 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-destructuring --harmony-default-parameters
+
+(function testExpressionTypes() {
+  "use strict";
+  ((x, y = x) => assertEquals(42, y))(42);
+
+  ((x, y = (x)) => assertEquals(42, y))(42);
+  ((x, y = `${x}`) => assertEquals("42", y))(42);
+  ((x, y = x = x + 1) => assertEquals(43, y))(42);
+  ((x, y = x()) => assertEquals(42, y))(() => 42);
+  ((x, y = new x()) => assertEquals(42, y.z))(function() { this.z = 42 });
+  ((x, y = -x) => assertEquals(-42, y))(42);
+  ((x, y = ++x) => assertEquals(43, y))(42);
+  ((x, y = x === 42) => assertTrue(y))(42);
+  ((x, y = (x == 42 ? x : 0)) => assertEquals(42, y))(42);
+
+  ((x, y = function() { return x }) => assertEquals(42, y()))(42);
+  ((x, y = () => x) => assertEquals(42, y()))(42);
+
+  // Literals
+  ((x, y = {z: x}) => assertEquals(42, y.z))(42);
+  ((x, y = {[x]: x}) => assertEquals(42, y[42]))(42);
+  ((x, y = [x]) => assertEquals(42, y[0]))(42);
+  ((x, y = [...x]) => assertEquals(42, y[0]))([42]);
+
+  ((x, y = class {
+    static [x]() { return x }
+  }) => assertEquals(42, y[42]()))(42);
+  ((x, y = (new class {
+    z() { return x }
+  })) => assertEquals(42, y.z()))(42);
+
+  // Scope chain of named class literals is busted
+  //((x, y = (new class Y {
+  //  static [x]() { return x }
+  //  z() { return Y[42] }
+  //})) => assertEquals(42, y.z()))(42);
+
+  // Defaults inside destructuring
+  ((x, {y = x}) => assertEquals(42, y))(42, {});
+  ((x, [y = x]) => assertEquals(42, y))(42, []);
+})();
+
+(function testMultiScopeCapture() {
+  "use strict";
+  var x = 1;
+  {
+    let y = 2;
+    ((x, y, a = x, b = y) => {
+      assertEquals(x, a);
+      assertEquals(y, b);
+    })(3, 4);

[rossberg, 2015/10/16 11:55:41]

Perhaps also return x and y and verify on the outside that they were indeed
bound to 3 and 4.

[adamk, 2015/10/16 13:38:28]

Done (though I just put the test inside the function instead).

+  }
+})();