[es6] Function length property should be configurable

test/mjsunit/es6/function-length-configurable.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.
+
+function getStrictF() {
+  'use strict';
+  return function f(x) {};
+}
+
+
+function getSloppyF() {
+  return function f(x) {};
+}
+
+
+function getStrictGenerator() {
+  'use strict';
+  return function* f(x) {};
+}
+
+
+function getSloppyGenerator() {
+  return function* f(x) {};
+}
+
+
+function test(testFunction) {
+  testFunction(getStrictF());
+  testFunction(getSloppyF());
+  testFunction(getStrictGenerator());
+  testFunction(getSloppyGenerator());
+}
+
+
+function testDescriptor(f) {
+  var descr = Object.getOwnPropertyDescriptor(f, 'length');
+  assertTrue(descr.configurable);
+  assertFalse(descr.enumerable);
+  assertEquals(1, descr.value);
+  assertFalse(descr.writable);
+}
+test(testDescriptor);
+
+
+function testSet(f) {
+  f.length = 2;
+  assertEquals(1, f.length);
+}
+test(testSet);
+
+
+function testSetStrict(f) {
+  'use strict';
+  assertThrows(function() {
+    f.length = 2;
+  }, TypeError);
+}
+test(testSetStrict);
+
+
+function testReconfigureAsDataProperty(f) {
+  Object.defineProperty(f, 'length', {
+    value: 2,
+  });
+  assertEquals(2, f.length);
+  Object.defineProperty(f, 'length', {
+    writable: true
+  });
+  f.length = 3;
+  assertEquals(3, f.length);
+
+  f.length = 42;
+  assertEquals(42, f.length);
+}
+test(testReconfigureAsDataProperty);
+
+
+function testReconfigureAsAccessorProperty(f) {
+  var length = 2;
+  Object.defineProperty(f, 'length', {
+    get: function() { return length; },
+    set: function(v) { length = v; }
+  });
+  assertEquals(2, f.length);
+  f.length = 3;
+  assertEquals(3, f.length);
+}
+test(testReconfigureAsAccessorProperty);
+
+
+(function testSetOnInstance() {
+  // This needs to come before testDelete below
+  assertTrue(Function.prototype.hasOwnProperty('length'));
+
+  function f() {}
+  delete f.length;
+  assertEquals(0, f.length);
+
+  f.length = 42;
+  assertEquals(0, f.length);  // non writable prototype property.
+  assertFalse(f.hasOwnProperty('length'));
+
+  Object.defineProperty(Function.prototype, 'length', {writable: true});
+
+  f.length = 123;
+  assertTrue(f.hasOwnProperty('length'));
+  assertEquals(123, f.length);
+})();
+
+
+(function testDelete() {
+  function f(x) {}
+  assertTrue(delete f.length);
+  assertFalse(f.hasOwnProperty('length'));
+  assertEquals(0, f.length);
+
+  assertTrue(delete Function.prototype.length);
+  assertEquals(undefined, f.length);
+})();