Bug 287078 – REGRESSION (283036@main): Some linear() WPT tests started failing

• Status: RESOLVED
• Resolution: WONTFIX
• Component: Animations

[Bramus]

I noticed that there is a regression in passing WPTs for linear():

- Safari 18.1: 21/21 PASS [^1]
- Safari 18.2: 18/21 PASS [^2] 

Looking at https://webstatus.dev/features/linear-easing?q=linear, the drop in passing tests was introduced on Dec 12 2024, around the time Safari Technology Preview 210 was released.

I couldn’t immediately find a bug that tracks this, so I’m filing this new one.

[^1]: https://wpt.fyi/results/css/css-easing/linear-timing-functions-syntax.html?label=stable&label=master&product=safari-18.1%20%2820619.2.8.11.10%29&aligned&q=linear
[^2]: https://wpt.fyi/results/css/css-easing/linear-timing-functions-syntax.html?label=master&label=stable&product=safari-18.2%20%2820620.1.16.11.8%29&aligned&q=linear

[Anthony Ricaud]

Running https://github.com/WebKit/webkit/blob/main/Tools/Scripts/bisect-builds could help narrow down the commit that introduced the issue.

[Radar WebKit Bug Importer]

<rdar://problem/144256867>

[Antoine Quint]

Good catch Bramus, I found STP 203 to be the first build to introduce this issue:

https://wpt.fyi/results/css/css-easing/linear-timing-functions-syntax.html?label=master&label=experimental&product=safari-202%20preview&aligned

https://wpt.fyi/results/css/css-easing/linear-timing-functions-syntax.html?label=master&label=experimental&product=safari-203%20preview&aligned

Going to bisect WebKit commits to find the exact regression point.

[Antoine Quint]

Oddly, this test passes within the WebKit test harness but definitely fails when loading live in Safari or Safari Technology Preview:

http://wpt.live/css/css-easing/linear-timing-functions-syntax.html

[Antoine Quint]

The commit range between STP 202 and STP 203 is 282390@main:283042@main according to https://webkit.org/blog/15860/release-notes-for-safari-technology-preview-203/.

[Antoine Quint]

This regressed with 283036@main. Cc'ing Sam Weinig who landed that patch.

[Sam Weinig]

This was just me failing to upstream my WPT changes :(. 

Here is the PR to do that now -> https://github.com/web-platform-tests/wpt/pull/50533.

[Bramus]

Phew!