[Webkit-unassigned] [Bug 206724] Nullptr crash when setting custom properties on detached style

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=206724

--- Comment #9 from Ryosuke Niwa <rniwa at webkit.org> ---
(In reply to Darin Adler from comment #8)
> Comment on attachment 388631 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=388631&action=review
> 
> >>> Source/WebCore/css/PropertySetCSSStyleDeclaration.cpp:260
> >>> +        ASSERT(document);
> >> 
> >> Why is this assertion safe? Since m_lastDocument is a WeakPtr, what guarantees it won’t be null?
> > 
> > This assert shouldn't be here, it's a leftover from debugging. setCustomProperty can handle null document, the crash was from assuming there would always be a parentStyleSheet() when there isn't a parentElement().
> 
> If parentStyleSheet is null too, then why can't we let document be null? Why
> do we need this m_lastDocument trick?

If document is null, then we wouldn't be able to get to the custom property registry & parse the property as "*" as opposed to whatever syntax currently defined by the author script. On the other hand, that's not a terrible outcome for now since custom registry isn't really something we currently ship.

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