Bug 304347 – REGRESSION(293848@main): In certain circumstances, -webkit-box-shadow (and perhaps other prefixed and/or cascade-alias properties) does not transition

• Component: Animations
• Status: RESOLVED FIXED

[Sam Weinig]

Created attachment 477769 [details]
Transition using box-shadow (works)

I am not sure exactly what the requirements are, but in some circumstances, using `-webkit-box-shadow` rather than `box-shadow` will cause a CSS transition not to occur.

See two attached test cases.

In the one called "Transition using box-shadow (works)", you will see that the transition happens, and there is a visible box shadow.
In the one called "Transition using -webkit-box-shadow (broken)", you will see that the transition does not happen, and there is no visible box shadow.

[Sam Weinig]

Created attachment 477770 [details]
Transition using -webkit-box-shadow (broken)

[Antoine Quint]

With both tests I see two transitions being started in Safari (one for -webkit-box-shadow, one for box-shadow), whereas Chrome and Firefox only start one (for box-shadow). I'm not seeing what you're seeing. What version of Safari did you test with?

[Antoine Quint]

I don't know whether a spec dictates the behavior for aliases here, but it would be nice to align with Chrome and Firefox here and codify this in WPT.

[Sam Weinig]

Interesting! I was testing with Safari Version 26.1 (21622.2.11.11.9). I will try ToT.

[Radar WebKit Bug Importer]

<rdar://problem/167144768>

[Antoine Quint]

Hmm, now I see the issue with the "broken" test with STP 234 and 305425@main, trying to identify when this regressed compared to what we shipped in macOS Sequoia 15.6.1 (24G90). My first regression range is 289651@main → 297306@main, will get a more specific regression point tomorrow.

[Antoine Quint]

This broke in 293848@main, the fix for bug 285900.

[Antoine Quint]

The behavior where two transitions were yielded when `transition-property: all` was used and a property with an alias changed was modified in 304641@main and it now matches Chrome and Firefox where a single transition occurs. Very nice.

[Antti Koivisto]

Pull request: https://github.com/WebKit/WebKit/pull/56649

[EWS]

Committed 305660@main (288510351274): <https://commits.webkit.org/305660@main>

Reviewed commits have been landed. Closing PR #56649 and removing active labels.