279012 2024-09-02 03:51:04 -0700 Transitioning Unregistered Custom Properties cause a transition loop 2024-09-04 00:04:54 -0700 1 1 1 Unclassified WebKit Animations Other Unspecified Unspecified RESOLVED FIXED https://github.com/web-platform-tests/wpt/pull/47939 InRadar P2 Normal --- 1 bramus graouts graouts graouts jaffathecake koivisto webkit-bug-importer oldest_to_newest 2056975 0 bramus 2024-09-02 03:51:04 -0700 (This bug was discovered while building `@bramus/style-observer`, a library that responds to changes in computed styles. For this it relies on CSS Transitions and `transition-behavior: allow-discrete`. See https://brm.us/style-observer for details about this library.) Transitioning Unregistered Custom Properties cause a transition loop - Demo: https://allow-discrete-bugs.netlify.app/safari/unregistered-loop/ – the custom properties `--variable1` and `--variable2` are not registered. - Expected behavior: When clicking the `--variable1` or `--variable2` buttons, the output should change and the transition should have triggered only once. - Actual Behavior: While the output does change, the transition is repeatedly triggered. You can verify this by checking the console, which logs `"_handleUpdate"` on `transitionstart` Tested in Safari Technology Preview 202 2057013 1 graouts 2024-09-02 07:06:37 -0700 Hi Bramus, thanks for the report. I'll probably get to it myself eventually, but could you perhaps make a reduction that does not involve any third-party script? It could help reduce the complexity and help identifying the source of the bug. Thank you. 2057015 2 jaffathecake 2024-09-02 07:20:25 -0700 Here's a reduction https://output.jsbin.com/pejadit/3/quiet 2057016 3 jaffathecake 2024-09-02 07:21:35 -0700 Expected: A single transitionstart event for the single style change. Actual: transitionstart appears to fire every frame thereafter. 2057043 4 graouts 2024-09-02 10:11:52 -0700 That's excellent, thank you. 2057049 5 graouts 2024-09-02 10:21:18 -0700 We enter this clause in `updateCSSTransitionsForStyleableAndProperty` for each style resolution: // 4. Otherwise, implementations must cancel the running transition and start a new transition whose: I haven't worked out what is failing to take us here. 2057051 6 graouts 2024-09-02 10:26:23 -0700 Presumably it's the propertyInStyleMatchesValueForTransitionInMap() call which returns false but it should return true. 2057053 7 graouts 2024-09-02 10:30:08 -0700 CSSPropertyAnimation::propertiesEqual() returns falses with none of the if statements in the custom property variant being hit. I assume this is because this is an unregistered property and we don't know how to compare values. 2057055 8 jaffathecake 2024-09-02 10:36:33 -0700 I believe the bug also happens if the property is registered as "*". Maybe even <custom-ident> too. 2057056 9 bramus 2024-09-02 10:40:11 -0700 (In reply to Jake Archibald from comment #8) > I believe the bug also happens if the property is registered as "*". Maybe > even <custom-ident> too. Yes, that would be https://bugs.webkit.org/show_bug.cgi?id=279013 It happens for `"*"` but not for `"<custom-ident>"`, though. 2057191 10 graouts 2024-09-03 02:30:05 -0700 *** Bug 279013 has been marked as a duplicate of this bug. *** 2057212 11 graouts 2024-09-03 06:00:12 -0700 Pull request: https://github.com/WebKit/WebKit/pull/33061 2057213 12 graouts 2024-09-03 06:03:24 -0700 Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/47939 2057284 13 ews-feeder 2024-09-03 10:10:38 -0700 Committed 283099@main (7f45cbdcfbf5): <https://commits.webkit.org/283099@main> Reviewed commits have been landed. Closing PR #33061 and removing active labels. 2057285 14 webkit-bug-importer 2024-09-03 10:11:15 -0700 <rdar://problem/135205514> 2057317 15 jaffathecake 2024-09-03 11:16:05 -0700 Thank you for fixing this so quickly! 2057492 16 graouts 2024-09-04 00:04:54 -0700 Thanks for filing with a simple test case, that's a lot of the work towards a fix already done :)