[ESnext] Implement Object Rest

test/mjsunit/harmony/object-rest-basic.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-object-rest-spread
+var { ...x } = { a: 1 };
+assertEquals({ a: 1 }, x);
+
+var { ...x } = { a: 1, b: 1 };
+assertEquals({ a: 1, b: 1 }, x);
+
+var { y, ...x } = { y: 1, a: 1 };
+assertEquals({ a: 1 }, x);
+assertEquals(1, y);
+
+({ a, ...b } = { a: 1, b: 2 });
+assertEquals(1, a);
+assertEquals({ b: 2 }, b);
+
+var { ...x } = {};
+assertEquals({}, x);
+
+var key = "b";
+var { [key]: y, ...x } = { b: 1, a: 1 };
+assertEquals({ a: 1 }, x);
+assertEquals(1, y);
+
+var key = 1;
+var { [key++]: y, ...x } = { 1: 1, a: 1 };
+assertEquals({ a: 1 }, x);
+assertEquals(key, 2);
+assertEquals(1, y);
+
+function example({a, ...rest}, { b = rest }) {
+    assertEquals(1, a);
+    assertEquals({ b: 2, c: 3}, rest);
+    assertEquals({ b: 2, c: 3}, b);
+};
+example({ a: 1, b: 2, c: 3}, { b: undefined });
+
+var x = { a: 3 };
+var y = {
+  set a(val) { assertUnreachable(); },
+  ...x,
+};
+assertEquals(y.a, 3);