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fix(virtual-core): don't replay iOS-deferred size corrections after an in-flight scrollToIndex lands - #1305
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…n in-flight scrollToIndex lands
🦋 Changeset detectedLatest commit: d2d8e9e The changes in this PR will be included in the next version bump. This PR includes changesets to release 9 packages
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📝 Walkthrough
Merge Risk: ⚪ Minimal · up to The change stops iOS size corrections deferred during an in-flight index scroll from being replayed after the scroll settles, and it refreshes measurements before reconciling. The previously identified stale-measurement risk is addressed. No remaining merge-blocking risk is evident. Pre-merge checks |
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| Check name | Status | Explanation |
|---|---|---|
| Linked Issues check |  |
Issue #1304 requires deferred iOS size corrections during an active scrollToIndex to avoid replay after reconciliation. applyScrollAdjustment now omits accumulation while `scrollState.index != nul… |
| Out of Scope Changes check | |
The source changes directly address issue #1304. The measurement rebuild supports correct reconciliation when the cache is stale. The regression test and changeset support the fix and release. No unre… |
| Docstring Coverage | |
No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2… |
| Title check | |
The title clearly and concisely identifies the primary fix: preventing replay of iOS-deferred size corrections after an in-flight scrollToIndex completes. |
| Description check | |
The description is complete and follows the repository template. It explains the cause, implementation, scope, testing, checklist status, release impact, and changeset. It also documents the environme… |
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Actionable comments posted: 1
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Inline comments:
Review comments at @packages/virtual-core/src/index.ts:
- Around line 792-794: Update resizeItem and the reconcileScroll path so
measurements are rebuilt before calculating the reconciliation target during an
index scroll, or keep the correction delta available until reconciliation uses
updated measurements; do not discard it while measurementsCache still contains
the old target.
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📒 Files selected for processing (3)
.changeset/ios-index-scroll-deferral.mdpackages/virtual-core/src/index.tspackages/virtual-core/tests/index.test.ts
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…croll A resize that no render has read yet left measurementsCache stale, so reconcileScroll could retire an index scroll at the old target now that the iOS-deferred delta is no longer replayed.
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Thanks @phcorp for the clear issue and the fix! I verified both parts are needed, and the regression test covers them well. Merging. 🙏 |
… a custom adjust predicate With scrollPaddingStart, rows above a start-aligned target are visible, so their growth moves the target without being owed to the viewport. A custom shouldAdjustScrollPositionOnItemSizeChange may opt out of compensation that the target drift would add back. Leave both to the no-compensation behaviour of TanStack#1305. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
With lanes > 1, rows in other lanes can span the fold and a resize can move the target to another lane, so its drift no longer matches the growth resizeItem would have compensated (e.g. drift 30 where 50 was owed). Keep TanStack#1305's no-compensation behaviour there. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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🎯 Changes
Fixes #1304.
On iOS WebKit,
applyScrollAdjustmentdefers a size correction into_iosDeferredAdjustmentwhile the scroller is live. While ascrollToIndexis in flight, though,reconcileScrollretargets from fresh measurements (getOffsetForIndex), so it already absorbs the resize. Once the scroll settles,_flushIosDeferredIfReadyreplays the deferred delta on top of the reconciled landing. The list overshoots the index target by the summed corrections.#1235 cleared a deferral that is pending when an absolute command starts. This change covers deltas deferred while an index scroll travels:
applyScrollAdjustmentdoes not accumulate the delta whilescrollState.index != null. The deferral itself is kept, so noscrollTopwrite interrupts the scroll, and reconcile does the correction. Offset-only scroll states (scrollToOffset) and user scrolls behave exactly as before.For reconcile to do that correction, it must see the resize.
getOffsetForIndexreadsmeasurementsCache, which onlygetMeasurements()rebuilds, so a resize that no render has read yet (no-oponChange, or a render after the rAF) left reconcile on the old target.reconcileScrollnow rebuilds measurements before computing the target. The rebuild is memoized onitemSizeCacheVersion, so it costs nothing when no size has changed. This part runs on every platform, and only makes index targets current sooner.Seen in production: chapter tabs in an iOS reader (
scrollToIndexto the chapter heading) landed on the heading, then slid past it. The deferral change alone has shipped in production as a pnpm patch.Testing
iOS deferral: a resize during an in-flight scrollToIndex is not replayed after it lands. Onmainit ends at scrollTop 1100 instead of 1050. With only the deferral change it ends at 1000 (stale reconcile target). It passes with both changes.virtual-coresuite 190/190,react-virtualunit 10/10,tsc, eslint and prettier clean.pnpm run test:pr: everything passes except e2e tasks that only failed for environmental reasons on my machine (missing Playwright browser; after installing it, the react-virtualchat.spec.tsprepend test fails in the full parallel run on untouchedmaintoo, and passes 3/3 alone on this branch).✅ Checklist
pnpm run test:pr.🚀 Release Impact
Summary by CodeRabbit
scrollToIndextarget no longer cause the final position to overshoot.