[Webkit-unassigned] [Bug 258282] REGRESSION (264594 at main): Broke custom element built-in polyfill by making form properties non deletable

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=258282

--- Comment #16 from Chris Dumez <cdumez at apple.com> ---
(In reply to Chris Dumez from comment #15)
> I wrote this very reduced test case which tries to delete property 0 of a
> form:
> https://codepen.io/cdumez/pen/JjeKgLa
> 
> Safari before 264594 at main: Able to delete the property
> Safari after 264594 at main: Not able to delete the property
> Chrome 114: Not able to delete the property
> Firefox 114: Not able to delete the property
> 
> So it seems like 264594 at main fixed a bug and aligned our behavior with
> Chrome & Firefox. Unfortunately, it also seems that the custom-elements
> polyfill was relying on said bug.
> 
> At this point, I think the best we could do is detect the policy and maybe
> quirk our behavior. I think this would also mean detecting the polyfill
> version so that we can have our new/standard behavior when using the fixed
> version of the polyfill.

Also, for the record, I believe that the part of 264594 at main that broke the polyfill was dropping this logic in the generated bindings:
https://github.com/WebKit/WebKit/commit/12544d4187162da11dad0451bceece73a83c4837#diff-635979f17a2f56f0ef3529de78480ad862a207ce15c096072b4e025a1e6b7428L1484

We used to mark indexed properties as configurable, but it didn't match Blink or Gecko.

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