Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: c6f11ac19f7a5ca1c9ca4f291ded204bfca751e1
https://github.com/WebKit/WebKit/commit/c6f11ac19f7a5ca1c9ca4f291ded204bfca751e1
Author: Simon Fraser <[email protected]>
Date: 2026-02-27 (Fri, 27 Feb 2026)
Changed paths:
A
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/anchor-used-height-change-does-not-suppress-expected.txt
A
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/anchor-used-height-change-does-not-suppress.html
A
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/negative-layout-overflow-on-anchor-expected.txt
A
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/negative-layout-overflow-on-anchor.html
M Source/WebCore/page/scrolling/ScrollAnchoringController.cpp
Log Message:
-----------
[Scroll Anchoring] Reddit page becomes blank and jumps to top after clicking
"View more comments"
https://bugs.webkit.org/show_bug.cgi?id=308788
rdar://170889205
Reviewed by Brent Fulgham.
On the reddit page, there's an intermediate state where the wrapper for the
comments (`SHREDDIT-COMMENT-TREE`)
has its content removed; its only child is a flexbox which has not been laid
out yet, so we pick the wrapper
as the anchor. The wrapper happens to have large overflow into negative top and
left, and this overflow
changes pre- to post-layout, so anchoring goes haywire.
Fix by trimming negative overflow when computing the local anchor rect; we
actually just use the anchor's
border box, extended in the block direction by layout overflow (since anchoring
only affects scrolling on
the block progression axis).
Added two new tests. `negative-layout-overflow-on-anchor.html` tests anchoring
with changing negative
overflow on the anchor. `anchor-used-height-change-does-not-suppress.html` was
added to test another scenario
I investigated while coming up with the fix, which is an anchor whose used
height changes; in all browsers
this does not suppress anchoring.
Tests:
imported/w3c/web-platform-tests/css/css-scroll-anchoring/anchor-used-height-change-does-not-suppress.html
imported/w3c/web-platform-tests/css/css-scroll-anchoring/negative-layout-overflow-on-anchor.html
*
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/anchor-used-height-change-does-not-suppress-expected.txt:
Added.
*
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/anchor-used-height-change-does-not-suppress.html:
Added.
*
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/negative-layout-overflow-on-anchor-expected.txt:
Added.
*
LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-anchoring/negative-layout-overflow-on-anchor.html:
Added.
* Source/WebCore/page/scrolling/ScrollAnchoringController.cpp:
(WebCore::candidateLocalRectForAnchoring):
(WebCore::ScrollAnchoringController::computeScrollerRelativeRects const):
(WebCore::ScrollAnchoringController::adjustScrollPositionForAnchoring):
Canonical link: https://commits.webkit.org/308352@main
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