The following layout test is flaky on iOS Simulator Release WK2 scrollingcoordinator/ios/ui-scroll-fixed.html Probable cause: Test was added in https://trac.webkit.org/changeset/242683/webkit A note was made on previous bug, but a fix does not appear to have been made. Flakiness Dashboard: https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=scrollingcoordinator%2Fios%2Fui-scroll-fixed.html Diff: https://build.webkit.org/results/Apple%20iOS%2012%20Simulator%20Release%20WK2%20(Tests)/r243869%20(3458)/scrollingcoordinator/ios/ui-scroll-fixed-diff.png
<rdar://problem/49612867>
Marked flaky in https://trac.webkit.org/changeset/243881/webkit while waiting for a fix
I can reproduce. This only seems to happen if amount scrolled (50px) is identical to the top of #container, so we must have an early return in code somewhere.
Created attachment 381146 [details] Patch
Comment on attachment 381146 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=381146&action=review > LayoutTests/ChangeLog:14 > + This test hit a really obscure bug where a combination of an immediate scroll, and > + an ancestor reposition left the layer position of a position:fixed layer unchanged. > + The position of this layer in the UI process had been previously modified by > + the scrolling tree for the scroll, but because the WebContent-side mutations left > + the actual position unchanged, we'd never apply a new position via a commit, so left > + the layer in the wrong location. Would this be fixed by a web->ui message that that signals we did a compositing layer update but nothing changed, so we are skipping the commit? This would just call applyLayerPositionsAfterCommit() to check for m_wasScrolledByDelegatedScrollingSincePreviousCommit bit. > LayoutTests/ChangeLog:19 > + Since this is so hard to hit with noisy user scrolling, just change the test to avoid > + the perfect storm of scrolls and offsets. Since we have managed to make a test for this it bit sad to let it go waste.
I filed bug 203112 to cover the underlying bug.
The commit-queue encountered the following flaky tests while processing attachment 381146 [details]: imported/w3c/web-platform-tests/mathml/presentation-markup/operators/mo-form-fallback.html bug 203076 (authors: fred.wang@free.fr and rwlbuis@gmail.com) imported/w3c/web-platform-tests/websockets/bufferedAmount-unchanged-by-sync-xhr.any.worker.html bug 202003 (author: youennf@gmail.com) The commit-queue is continuing to process your patch.
Comment on attachment 381146 [details] Patch Clearing flags on attachment: 381146 Committed r251251: <https://trac.webkit.org/changeset/251251>
All reviewed patches have been landed. Closing bug.