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…st-jump reflow Jump to the end of a long flow-layout list, then scroll to 0 on the next frame. The scroll to the top is currently undone: scrollTop ends near the bottom (~48500 in the default fixture) and item 0 is not rendered. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_013imjkuZ1miKJ7HzHWg6Ku2 Signed-off-by: Aleksandr Tarutin <atarutin@orionsbelt.net>
…render range After a jump into unmeasured rows, the flow layout keeps its anchor until the layout is stable. A new scroll position that lands in that window was measured against the stale anchor; _getItems computed an anchorErr, added it to _scrollError, and the virtualizer scrolled back to the anchor. Choose a new anchor when the old one is outside [lower, upper]. The change is the anchor-validation hunk from Gray Norton's lit#5279. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_013imjkuZ1miKJ7HzHWg6Ku2 Signed-off-by: Aleksandr Tarutin <atarutin@orionsbelt.net>
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Fixes #5418
Bug
After a jump into unmeasured rows (for example,
scrollTop = scrollHeighton a long flow-layout list), the flow layout keeps its anchor (the last item) until the layout is stable. If the user scrolls somewhere else during that window,_getItemsmeasures the new position against the stale anchor. It computesanchorErr, adds it to_scrollError, and_correctScrollErrorscrolls the viewport back to the anchor. A scroll to the top made one frame after a jump to the end leaves the list at the bottom.Fix
Re-pick the anchor when
_anchorPosis outside[lower, upper]. This is the anchor-validation hunk from @graynorton's #5279, taken by itself so it can land without the rest of that stack (#5249). Only the code comment differs, because the freeze/unfreeze API that #5279's comment refers to isn't onmain.Test
src/test/scenarios/scroll-jump-anchor.test.tsjumps to the end, scrolls to 0 on the next frame, and asserts thatscrollTop < 50and that item 0 is rendered. It covers<lit-virtualizer>andvirtualize()withscroller, and<lit-virtualizer>with window scrolling.scrollTopis 48550, 48550 and 48358. They failed the same way on 4 runs.CI=true, and 117 passed without it, including theskipInCIscrolling tests.tsc --target ES5, eslint and prettier are clean.The test is a separate commit, so it can be checked out before the fix.
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https://claude.ai/code/session_013imjkuZ1miKJ7HzHWg6Ku2