Bug 244808 – Forgiving selectors should not be reported as supported with CSS.supports("selector(...)")

• Component: CSS
• Status: RESOLVED FIXED

[Michał Gołębiowski-Owczarek]

CSS.supports() and @supports should return false for unrecognized selectors in per CSSWG resolution in https://github.com/w3c/csswg-drafts/issues/7280

For why this matters for jQuery, see this comment:
https://github.com/w3c/csswg-drafts/issues/7676#issuecomment-1235714917
and that whole issue in general.

tl;dr is that jQuery has custom selector extensions but for performance reasons it first tries to run a provided selector through `querySelectorAll` and only when that fails it uses its own custom DOM traversal. However, this approach doesn't work for pseudo-classes using forgiving selector lists as parameters - like `:has()`. jQuery would like to migrate to testing the selector via `CSS.supports("selector(...)")` instead but right now it returns `true` for `:has(:gibberish)` as well. The linked CSS WG resolution makes the API return `false` in such cases, making it a viable tool for jQuery.

Chromium bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1359396
Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1789248

[Karl Dubost]

Already fixed in Firefox
https://bugzilla.mozilla.org/show_bug.cgi?id=1789248

And in Chrome
https://bugs.chromium.org/p/chromium/issues/detail?id=1359396

[Radar WebKit Bug Importer]

<rdar://problem/99682164>

[Antti Koivisto]

Created attachment 462332 [details]
Patch

[EWS]

Committed 254489@main (fc2b16c5035f): <https://commits.webkit.org/254489@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 462332 [details].