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fix(mobile): Android diff no longer stalls when comment cards scroll into view - #25994
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ApprovabilityVerdict: Approved at Macroscope's review found this PR approvable — This is a narrowly scoped Android performance fix that replaces repeated text measurements in existing comment and notice rendering with a single fitting calculation, while adding a focused regression test. It does not change product defaults or introduce new capabilities, schemas, infrastructure, or sensitive-area behavior. You can add or adjust custom eligibility rules. Learn more. |
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No actionable comments were generated in the recent review.
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| Layer / File(s) | Summary |
|---|---|
Prefix measurement and validation apps/mobile/modules/t3-review-diff/android/src/main/java/expo/modules/t3reviewdiff/T3ReviewDiffView.kt, apps/mobile/modules/t3-review-diff/tests/android/src/test/kotlin/expo/modules/t3reviewdiff/ReviewDiffGeometryTest.kt |
ellipsize is now module-visible and uses Paint.breakText to select a prefix. The test checks that a long comment uses at most two text measurements, ends with ..., and fits within 300 pixels. |
Priority:
Estimated code review effort: 2 (Simple) | ~10 minutes
Change: Bug fix
Suggested reviewers: juliusmarminge
Merge Risk: 
20b9c
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No merge-blocking risk was identified in the reviewed changes.
Pre-merge checks: 
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Check name Status Explanation Description check The description includes all required sections. It explains the Android performance problem, the Paint.breakText fix, scope and approval rationale, focused test results, emulator verification, before-… Title check The title clearly and concisely describes the main change: preventing Android diff scrolling stalls when comment cards enter view. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request. Full details: Description check
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Explanation
The description includes all required sections. It explains the Android performance problem, the Paint.breakText fix, scope and approval rationale, focused test results, emulator verification, before-and-after metrics, and the physical-device limitation.
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Closing as superseded by #26174, which fixes the same quadratic measurement and also caps the measured text. |
Problem
On Android, scrolling a pull request's changes stalls whenever a comment card is on screen. Each frame takes over a second when the comments are long, as bot reviews often are. Reproduce with
software-mansion/react-native-reanimated#10880: openSharedTransitions.cppand scroll past its comments on lines 375–395.Change
A comment card shows one line of its comment, cut to fit with "...". The cut removed one character at a time and re-measured the remaining text after each removal, on every frame. A 9,000-character comment meant thousands of text measurements per card per frame.
The cut now asks Android's text measurement for the fitting length in one call (
Paint.breakText). It also no longer splits an emoji or other surrogate pair in half. Notice rows use the same helper and get the same speedup.Scope and approval
A small fix for an obvious performance bug in the Android diff view. It changes one helper and adds a regression test. iOS draws comment cards differently and is not affected.
Verification
ellipsizingALongCommentDoesNotRemeasureItPerCharactercounts text measurements for one long comment. It fails before the fix (6,181 measurements) and passes after. The whole Android native suite (apps/mobile/modules/t3-review-diff/tests/run-android.sh) passes.dumpsys gfxinfo:Android emulator, software-mansion/react-native-reanimated#10880,
SharedTransitions.cpp, same swipes from line 233 down past the commentsandroid-before.mp4
android-after.mp4
Not checked on a physical Android device.
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