Bug 302533 – REGRESSION (STP 232): comma-separated values for mask-size: auto gets unset

• Component: CSS
• Status: RESOLVED FIXED

[sgraz]

Created attachment 477395 [details]
Image depicting before and after, using mask-size: auto value

In a comma-separated mask-size declaration like `mask-size: auto, 300%;` the auto value has historically behaved the same as setting a `100%` value. 

However since Release 232 (WebKit 21624.1.2.19.2) the `auto` value gets ignored, as seen in the Computed tab. The result is similar to using `unset`. 

I mention comma-separated because using a singular value like `mask-size: auto` sets the mask image to its intrinsic size rather than `100%`, which is consistent across most browsers I tested, including the latest Webkit. So the regression is only for comma-separated mask-size values. 

I don't know the exact mechanics of how the browser interprets comma vs single values in this case. But felt it was important to report the difference, it did affect a lot of my existing CSS effects relying on the auto value. 
 
Reproduction: 

Link: https://codepen.io/sebastiangraz/pen/VYaaMry

1. Use Safari Technology Preview Release 232
2. Edit the mask-size value from `mask-size: auto, 300%;` to `mask-size: 100%, 300%;` 
3. Note how the mask now works again as originally intended
4. Open same link with any other older browser like Safari 26.1, repeat the same change, and note how no change is seen.

[Alexey Proskuryakov]

Thank you for the report! Both Chrome and Firefox pass the test, so it's certainly not OK to change this behavior.

For others trying to reproduce this: note that both success and failure show up as green, one needs to pay closer attention to what's drawn.

[Radar WebKit Bug Importer]

<rdar://problem/164727930>

[Simon Fraser (smfr)]

Caused by the fix for bug 298113.

[Sam Weinig]

Pull request: https://github.com/WebKit/WebKit/pull/54110

[EWS]

Committed 303192@main (f27a04372bba): <https://commits.webkit.org/303192@main>

Reviewed commits have been landed. Closing PR #54110 and removing active labels.

[Ahmad Saleem]

Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/56121