LibWeb: Drop the post-pass anchor-inset writeback into computed values - #10943
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kalenikaliaksandr merged 1 commit intoJul 31, 2026
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Once the outermost layout pass returned, the bridge rewrote the computed inset values of every anchor-positioned box, replacing their anchor() functions with the pixel values the pass had resolved. The writeback dates from when the style itself was the carrier of resolved anchor insets: resolution overwrote the inset properties so that every later read, inside or after the pass, would see resolved pixels. Since 0d42286 the pass no longer works that way. Resolved anchor insets go into a per-pass override store, and every inset read inside the pass is masked by that store, so the pass is self-sufficient and the writeback could only matter to code running after layout. Neither of its two remaining consumers actually wants it: - getComputedStyle reports resolved insets through the used-value path, which reads the box model of the laid-out box. It does not need resolved pixels smuggled into computed values. - Later layout passes are actively harmed by it. With resolved pixels persisted in computed values, a relayout that skipped style recalc reused the previous pass's anchor positions even if the anchor had moved since, and the resolution early-out then cleared the stored default-anchor scroll shift without re-establishing it, silently losing scroll compensation. So the writeback machinery can simply go: the deferred-inset batch and its recording callback, the bridge's pending vector, and the writeback in ActiveLayoutPassScope's destructor. Anchor insets now resolve fresh in every pass from the pristine computed values, fixing the stale anchor positions and the lost scroll shift, and computed values become immutable from the moment a layout pass first reads them until the next style recalculation.
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📝 WalkthroughWalkthroughDeferred resolved-anchor-inset storage, callbacks, commit reporting, and pass-end application were removed. Absolute-position layout continues to update resolved anchor insets directly. ChangesAnchor-inset writeback
Estimated code review effort: 2 (Simple) | ~10 minutes Possibly related PRs
Suggested reviewers: 🚥 Pre-merge checks | ✅ 3✅ Passed checks (3 passed)
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Once the outermost layout pass returned, the bridge rewrote the computed inset values of every anchor-positioned box, replacing their anchor() functions with the pixel values the pass had resolved. The writeback dates from when the style itself was the carrier of resolved anchor insets: resolution overwrote the inset properties so that every later read, inside or after the pass, would see resolved pixels.
Since 0d42286 the pass no longer works that way. Resolved anchor insets go into a per-pass override store, and every inset read inside the pass is masked by that store, so the pass is self-sufficient and the writeback could only matter to code running after layout. Neither of its two remaining consumers actually wants it:
getComputedStyle reports resolved insets through the used-value path, which reads the box model of the laid-out box. It does not need resolved pixels smuggled into computed values.
Later layout passes are actively harmed by it. With resolved pixels persisted in computed values, a relayout that skipped style recalc reused the previous pass's anchor positions even if the anchor had moved since, and the resolution early-out then cleared the stored default-anchor scroll shift without re-establishing it, silently losing scroll compensation.
So the writeback machinery can simply go: the deferred-inset batch and its recording callback, the bridge's pending vector, and the writeback in ActiveLayoutPassScope's destructor. Anchor insets now resolve fresh in every pass from the pristine computed values, fixing the stale anchor positions and the lost scroll shift, and computed values become immutable from the moment a layout pass first reads them until the next style recalculation.