Fix Function subclassing.

test/mjsunit/es6/classes-subclass-builtins.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: --allow-natives-syntax --harmony-reflect --harmony-regexp-subclass
-// Flags: --expose-gc
+// Flags: --expose-gc --strong-mode
 
 "use strict";
 
 
 function checkPrototypeChain(object, constructors) {
   var proto = object.__proto__;
   for (var i = 0; i < constructors.length; i++) {
     assertEquals(constructors[i].prototype, proto);
     assertEquals(constructors[i], proto.constructor);
     proto = proto.__proto__;
@@ skipping 54 matching lines @@
 
   gc();
 })();
 
 
 (function() {
   class A extends Function {
     constructor(...args) {
       assertFalse(new.target === undefined);
       super(...args);
+      // Strong functions are not extensible, so don't add fields.
+      if (args[args.length - 1].indexOf("use strong") >= 0) return;
       this.a = 42;
       this.d = 4.2;
       this.o = {foo:153};
     }
   }
+  var sloppy_func = new A("");
+  var strict_func = new A("'use strict';");
+  assertNull(sloppy_func.caller);
+  assertThrows("strict_f.caller");
+  assertNull(Object.getOwnPropertyDescriptor(sloppy_func, "caller").value);
+  assertEquals(undefined, Object.getOwnPropertyDescriptor(strict_func, "caller"));
 
-  var o = new A("this.foo = 113;");
-  assertTrue(o instanceof Object);
-  assertTrue(o instanceof Function);
-  assertTrue(o instanceof A);
-  assertEquals("function", typeof o);
-  checkPrototypeChain(o, [A, Function, Object]);
-  assertEquals(42, o.a);
-  assertEquals(4.2, o.d);
-  assertEquals(153, o.o.foo);
-  var oo = new o();
+  var sloppy_func = new A("this.foo = 113;");
+  assertTrue(undefined !== sloppy_func.prototype);
+  sloppy_func.prototype.bar = 377;
+  assertTrue(sloppy_func instanceof Object);
+  assertTrue(sloppy_func instanceof Function);
+  assertTrue(sloppy_func instanceof A);
+  assertEquals("function", typeof sloppy_func);
+  checkPrototypeChain(sloppy_func, [A, Function, Object]);
+  assertEquals(42, sloppy_func.a);
+  assertEquals(4.2, sloppy_func.d);
+  assertEquals(153, sloppy_func.o.foo);
+  var oo = new sloppy_func();
   assertEquals(113, oo.foo);
+  assertEquals(377, oo.bar);
 
-  var o1 = new A("return 312;");
-  assertTrue(%HaveSameMap(o, o1));
+  var sloppy_func1 = new A("return 312;");
+  assertTrue(%HaveSameMap(sloppy_func, sloppy_func1));
+
+
+  var strict_func = new A("'use strict'; this.foo = 113;");
+  assertFalse(%HaveSameMap(strict_func, sloppy_func));
+
+  var strict_func1 = new A("'use strict'; return 312;");
+  assertTrue(%HaveSameMap(strict_func, strict_func1));
+
+
+  var strong_func = new A("'use strong'; this.foo = 113");
+  assertFalse(%HaveSameMap(strong_func, sloppy_func));
+  assertFalse(%HaveSameMap(strong_func, strict_func));
+
+  var strong_func1 = new A("'use strong'; return 312;");
+  assertTrue(%HaveSameMap(strong_func, strong_func1));
 
   gc();
 })();
 
 
 (function() {
   class A extends Boolean {
     constructor(...args) {
       assertFalse(new.target === undefined);
       super(...args);
@@ skipping 710 matching lines @@
 
   Object.defineProperty(pattern, Symbol.match, {
     get() { log.push("match"); f.prototype = p2; return false; }});
 
   var o = Reflect.construct(RegExp, [pattern], f);
   assertEquals(["match", "tostring"], log);
   assertEquals(/biep/, o);
   assertTrue(o.__proto__ === p2);
   assertTrue(f.prototype === p3);
 })();