Bug 80577 – Object.freeze broken on latest Nightly

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Mark S. Miller]

When executing the following three lines on Safari Version 5.1.3 (7534.53.10), the last correctly returned true. On WebKit Nightly Version 5.1.3 (7534.53.10, r110098), it gives false, which is wrong.

> function foo(){}
> Object.freeze(foo);
> Object.isFrozen(foo);

The problem seems to be the prototype property. On WebKit Nightly

> JSON.stringify(Object.getOwnPropertyDescriptor(foo, 'prototype'))
{"value":{},"writable":true,"enumerable":false,"configurable":false}

On Safari, we instead get the correct "writable":false

For some reason, it seems this same problem manifests differently on http://es-lab.googlecode.com/svn/trunk/src/ses/explicit.html

When freezing a particular function with a writable non-configurable prototype, this page now throws 

      "TypeError: Attempting to change access mechanism for an unconfigurable property" 

on this latest Nightly. It did not do so on last night's Nightly. From the nature of this symptom, I'm not sure that the problem is with the 'prototype' property specifically, since the error doesn't say what property it is complaining about. Regardless, it is never correct from Object.freeze itself to fail because of (non) configurability. All the state changes it causes are always allowed.

[Gavin Barraclough]

Ugh, will look into this.  I'm guessing this is related to the fact the prototype property is added lazily, but haven't figured out exactly what went wrong here.

Cheers for the bug report Mark.

[Gavin Barraclough]

Created attachment 131147 [details]
Fix

[Gavin Barraclough]

Fixed in r110396

[Mark S. Miller]

On r110411 visiting http://es-lab.googlecode.com/svn/trunk/src/ses/explicit.html I'm still seeing

    TypeError: Attempting to change access mechanism for an unconfigurable property

thrown when freezing a function. Reopening.

[Gavin Barraclough]

Gah, I bet I know what this is.  The problem is probably preventExtension then freeze.

[Gavin Barraclough]

Created attachment 132663 [details]
More fixed!

[Gavin Barraclough]

Fixed in r111250 - last time I forgot to check http://eslab.googlecode.com/svn/trunk/src/ses/explicit.html - this time I did, & looks like all is good, so hopefully this bug is fully fixed now!

Thanks for the bug report Mark, cheers, G.