309019 2026-03-02 16:26:53 -0800 REGRESSION(308215@main): [iOS] imported/w3c/web-platform-tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll.html?include=root-scrollBy-auto is a flaky text failure 2026-04-02 15:06:51 -0700 1 1 1 Unclassified WebKit Scrolling WebKit Nightly Build Unspecified Unspecified NEW https://bugs.webkit.org/show_bug.cgi?id=311235 InRadar P2 Normal --- 1 d_delatoba d_delatoba simon.fraser webkit-bot-watchers-bugzilla webkit-bug-importer oldest_to_newest 2186307 0 d_delatoba 2026-03-02 16:26:53 -0800 imported/w3c/web-platform-tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll.html?include=root-scrollBy-auto is a flaky text failure on iOS HISTORY: https://results.webkit.org/?suite=layout-tests&test=imported%2Fw3c%2Fweb-platform-tests%2Fdom%2Fevents%2Fscrolling%2Fscrollend-event-fired-for-programmatic-scroll.html%3Finclude%3Droot-scrollBy-auto DIFF: --- /Volumes/Data/worker/Apple-iOS-26-Simulator-Release-WK2-Tests/build/layout-test-results/imported/w3c/web-platform-tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll_include=root-scrollBy-auto-expected.txt +++ /Volumes/Data/worker/Apple-iOS-26-Simulator-Release-WK2-Tests/build/layout-test-results/imported/w3c/web-platform-tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll_include=root-scrollBy-auto-actual.txt @@ -1,3 +1,3 @@ -PASS Tests scrollend event for calling scrollBy with behavior 'auto' on root. +FAIL Tests scrollend event for calling scrollBy with behavior 'auto' on root. assert_equals: HTML.scrollBy scrollLeft expected 200 but got 0 DIFF URL: https://build.webkit.org/results/Apple-iOS-26-Simulator-Release-WK2-Tests/308467%40main%20(1971)/imported/w3c/web-platform-tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll_include=root-scrollBy-auto-pretty-diff.html REPRODUCTION: I was able to reproduce on iOS 26.2 with the following: run-webkit-tests --no-build --no-retry --no-show-results --exit-after-n-failures=1 --expect-pass --iterations=1000 --force --ios-simulator --release imported/w3c/web-platform-tests/dom/events/scrolling/scrollend-event-fired-for-programmatic-scroll.html I am going to mark expectations as pass fail while this pends investigation 2186308 1 webkit-bug-importer 2026-03-02 16:26:58 -0800 <rdar://problem/171569422> 2186310 2 d_delatoba 2026-03-02 16:33:25 -0800 Pull request: https://github.com/WebKit/WebKit/pull/59750 2186313 3 ews-feeder 2026-03-02 16:35:30 -0800 Test gardening commit 308493@main (81731012a37e): <https://commits.webkit.org/308493@main> Reviewed commits have been landed. Closing PR #59750 and removing active labels. 2195750 4 simon.fraser 2026-03-31 17:31:04 -0700 This happens because we get into WebPage::updateVisibleContentRects() when ViewUpdateDispatcher::visibleContentRectUpdate() fires, which is unpredictable, and that does not go through the logic in RemoteScrollingCoordinator::scrollUpdateForNode() that suppresses user scrolls while a programmatic scroll response is pending. The base issue here is that we lose the user/programmatic distinction for root scroller changes coming in via VisibleContentRects on iOS. 2196390 5 simon.fraser 2026-04-02 15:06:51 -0700 Even if we make ViewUpdateDispatcher more deterministic (pulling update rects at the start of each rendering update), things are still non-deterministic because of how the UI process batches `-[WKWebView _updateVisibleContentRects]` on a per CoreAnimation commit basis.