Bug 177070 – [JSC] Consider dropping JSObjectSetPrototype feature for JSGlobalObject

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

[Yusuke Suzuki]

Now, JSGlobalObject is an immutable prototype exotic object. It means that we cannot change the [[Prototype]] of JSGlobalObject.
However, our JSC API allows us to change it specially.

What do you think of dropping this feature?

[Geoffrey Garen]

Seems OK to me, to match the spec.

[Yusuke Suzuki]

Created attachment 321118 [details]
Patch

[Yusuke Suzuki]

Comment on attachment 321118 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=321118&action=review

> Source/JavaScriptCore/ChangeLog:15
> +        edge cases.

While we do not allow users to change [[Prototype]] of the global object, our JS API has the way to set custom [[Prototype]] of global object by setting "prototype" of JSClassRef.
So I think it's ok even in terms of the ability of JSC APIs.

[Saam Barati]

Comment on attachment 321118 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=321118&action=review

>> Source/JavaScriptCore/ChangeLog:15
>> +        edge cases.
> 
> While we do not allow users to change [[Prototype]] of the global object, our JS API has the way to set custom [[Prototype]] of global object by setting "prototype" of JSClassRef.
> So I think it's ok even in terms of the ability of JSC APIs.

Can we now constant fold toThis on global object? Why doesn't this patch remove the JSGlobalObject::resetPrototype API?

[Yusuke Suzuki]

Comment on attachment 321118 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=321118&action=review

>>> Source/JavaScriptCore/ChangeLog:15
>>> +        edge cases.
>> 
>> While we do not allow users to change [[Prototype]] of the global object, our JS API has the way to set custom [[Prototype]] of global object by setting "prototype" of JSClassRef.
>> So I think it's ok even in terms of the ability of JSC APIs.
> 
> Can we now constant fold toThis on global object? Why doesn't this patch remove the JSGlobalObject::resetPrototype API?

Not yet. I'm now removing resetPrototype things to perform constant folding GlobalThis by ensuring that prototype is not changed after instantiation.
But resetPrototype still exists in the other places. This patch is a first step to remove it.

[Yusuke Suzuki]

Comment on attachment 321118 [details]
Patch

Thank you for your reviews!

[WebKit Commit Bot]

Comment on attachment 321118 [details]
Patch

Clearing flags on attachment: 321118

Committed r222175: <http://trac.webkit.org/changeset/222175>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/34693228>