1789248 - Forgiving selectors should not be reported as supported with CSS.supports("selector(...)")

Status: RESOLVED FIXED

(Core :: DOM: CSS Object Model, task)

Description

[Michał Gołębiowski-Owczarek [:mgol]]

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

This bug has been ported from a Chromium one: https://bugs.chromium.org/p/chromium/issues/detail?id=1359396

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.

Comment 1

[Emilio Cobos Álvarez [:emilio]]

Yes, I proposed that change in fact, I just didn't get to fix it just yet :)

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1789248 - Disallow forgiving selector-parsing in @supports. r=#style,#layout

As per spec, see https://github.com/w3c/csswg-drafts/issues/7280

Comment 3

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1789248 - Remove @supports selector pref. r=#style,#layout

We've shipped it for a while.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3e0a5d1881e9
Disallow forgiving selector-parsing in @supports. r=firefox-style-system-reviewers,layout-reviewers,boris

Comment 5

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/35800 for changes under testing/web-platform/tests

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/07d280f89c51
Remove @supports selector pref. r=firefox-style-system-reviewers,layout-reviewers,boris

Comment 7

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/3e0a5d1881e9
https://hg.mozilla.org/mozilla-central/rev/07d280f89c51

Comment 8

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot