RESOLVED FIXED312831
REGRESSION (307593@main): position-area box in fast/scrolling/anchor-overscroll-fixed.html does not fallback properly 
https://bugs.webkit.org/show_bug.cgi?id=312831
Summary REGRESSION (307593@main): position-area box in fast/scrolling/anchor-overscro...
Kiet Ho
Reported 2026-04-20 16:27:40 PDT
Created attachment 479223 [details] Screen recording of the issue Steps to reproduce: * Open fast/scrolling/anchor-overscroll-fixed.html * Scroll up and down to make the teal box and aqua (border only) box change position due to position option fallback Expect: the teal and aqua box should fallback with each other Actual: the teal box does not fallback at all. Attached is a video of the issue on WebKit 307593@main.
Attachments
Screen recording of the issue (740.40 KB, video/quicktime)
2026-04-20 16:27 PDT, Kiet Ho 		no flags
Details
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Radar WebKit Bug Importer
Comment 1 2026-04-20 16:27:46 PDT
<rdar://problem/175203020>
fantasai
Comment 2 2026-04-21 13:16:45 PDT
I can't get a working build atm, but I think you should be able to fix the problem by removing these two lines in RenderBox::containingBlockRangeForPositioned() that are conditioned on `isFixedPositioned()`: if (!style().positionArea().isNone() && renderView->hasRenderOverflow()) return getScrollableContainingBlockRange(*renderView, physicalAxis); I'm trying to think why those two lines were added and coming up blank. So hopefully it's ok to just remove them. :) Don't remove the ones at the bottom of the function, or that'll regress non-fixed-positioned boxes.
fantasai
Comment 3 2026-04-22 13:12:19 PDT
Filed a follow-up on testing at https://bugs.webkit.org/show_bug.cgi?id=313020 fwiw.
Kiet Ho
Comment 4 2026-04-22 15:16:12 PDT
Pull request: https://github.com/WebKit/WebKit/pull/63363
Kiet Ho
Comment 5 2026-04-24 10:22:52 PDT
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/59454
EWS
Comment 6 2026-04-24 13:33:58 PDT
Committed 311981@main (aac4aed489d1): <https://commits.webkit.org/311981@main> Reviewed commits have been landed. Closing PR #63363 and removing active labels.
EWS
Comment 7 2026-04-24 18:40:47 PDT
Committed 305413.728@safari-7624-branch (294b842176b7): <https://commits.webkit.org/305413.728@safari-7624-branch> Reviewed commits have been landed. Closing PR #5048 and removing active labels.
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