Fix issue 720 making Object.defineProperty handle existing writable flags correctly.

The existing version will overwrite the existing writable flag with
false even in the case where no new value is given and the existing
writable flag is true.

The reason for the issue is that there is no check to see if the
provided descriptor actually has a writable attribute. This causes us
to use the default value (false) even in the case where nothing was
provided. In addition, the existing tests makes wrong assumptions (that writable is always set to false if not provided) and has been changed to follow the specification.

Review URL: http://codereview.chromium.org/2271001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4720 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/v8natives.js

@@ -604,7 +604,13 @@ function DefineOwnProperty(obj, p, desc, should_throw) {
     flag |= DONT_DELETE;
 
   if (IsDataDescriptor(desc) || IsGenericDescriptor(desc)) {
-    flag |= desc.isWritable() ? 0 : READ_ONLY;
+    if (desc.hasWritable()) {
+      flag |= desc.isWritable() ? 0 : READ_ONLY;
+    } else if (!IS_UNDEFINED(current)) {
+      flag |= current.isWritable() ? 0 : READ_ONLY;
+    } else {
+      flag |= READ_ONLY;
+    }
     %DefineOrRedefineDataProperty(obj, p, desc.getValue(), flag);
   } else {
     if (desc.hasGetter() && IS_FUNCTION(desc.getGet())) {

test/mjsunit/object-define-property.js

@@ -289,7 +289,7 @@ desc = Object.getOwnPropertyDescriptor(obj1, "foobar");
 assertEquals(obj1.foobar, 2000);
 assertEquals(desc.value, 2000);
 assertFalse(desc.configurable);
-assertFalse(desc.writable);
+assertTrue(desc.writable);
 assertFalse(desc.enumerable);
 assertEquals(desc.get, undefined);
 assertEquals(desc.set, undefined);
@@ -317,7 +317,7 @@ desc = Object.getOwnPropertyDescriptor(obj1, "foobar");
 assertEquals(obj1.foobar, 2000);
 assertEquals(desc.value, 2000);
 assertFalse(desc.configurable);
-assertFalse(desc.writable);
+assertTrue(desc.writable);
 assertFalse(desc.enumerable);
 assertEquals(desc.get, undefined);
 assertEquals(desc.set, undefined);

test/mjsunit/regress/regress-720.js

+// Copyright 2010 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// This regression test is used to ensure that Object.defineProperty
+// keeps the existing value of the writable flag if none is given
+// in the provided descriptor. 
+// See: http://code.google.com/p/v8/issues/detail?id=720
+
+var o = {x: 10};
+Object.defineProperty(o, "x", {value: 5});
+var desc = Object.getOwnPropertyDescriptor(o, "x");
+assertTrue(desc["writable"]);