Bug 165227 – Introduce the concept of Immutable Prototype Exotic Objects to comply with the spec.

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Mark Lam]

See https://tc39.github.io/ecma262/#sec-immutable-prototype-exotic-objects.

[Mark Lam]

<rdar://problem/29442665>

[Mark Lam]

Spec excerpts of relevance:

https://tc39.github.io/ecma262/#sec-properties-of-the-object-prototype-object
"The Object prototype object is an immutable prototype exotic object."

https://html.spec.whatwg.org/#the-windowproxy-exotic-object
https://html.spec.whatwg.org/#windowproxy-setprototypeof
https://html.spec.whatwg.org/#the-location-interface
https://html.spec.whatwg.org/#location-setprototypeof
- Based on these WindowProxy and Location both have their [[SetPrototypeOf]] functions unconditionally return false.  This differs from the immutable prototype exotic object which allows [[SetPrototypeOf]] to return true if the set value is the same as the existing prototype value.

[Mark Lam]

Created attachment 296251 [details]
proposed patch.

[Saam Barati]

Comment on attachment 296251 [details]
proposed patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=296251&action=review

r=me

> LayoutTests/js/script-tests/prototype-assignment.js:36
> +    let userAgent = navigator.userAgent;
> +    if (userAgent.match(/ Chrome\/[0-9]+/)) engine = "chrome";
> +    else if (userAgent.match(/ Firefox\/[0-9]+/)) engine = "default";
> +    else engine = "safari";

What's the point of this? Don't we already know the answer?

[Mark Lam]

Comment on attachment 296251 [details]
proposed patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=296251&action=review

>> LayoutTests/js/script-tests/prototype-assignment.js:36
>> +    else engine = "safari";
> 
> What's the point of this? Don't we already know the answer?

This is so I can run this test on Chrome and Firefox to compare results.  The test configures the error messages to check below based on the browser it is running on.

[Mark Lam]

Thanks for the review.  Landed in r209424: <http://trac.webkit.org/r209424>.