fix(Reanimated): preserve layout updates during entering animations

[ngocdevv]

Note

This pull request was authored by AI on behalf of @ngocdevv.

Summary

Fixes #10161.

React updates that do not have a configured layout transition are passed directly to the mounting layer. When such an update happens during an entering animation, the animation proxy kept the original finalView. The next animation frame was then based on that stale snapshot and reapplied the old layout metrics, leaving the native hit-testing bounds smaller than the visible content.

This change keeps the ongoing animation target synchronized with pass-through React updates in both the legacy and experimental Layout Animations proxies. The experimental proxy uses the LightNode's merged current view so Android diffed props are preserved as well.

Test plan

Manual regression test using the reproduction from https://github.com/mozzius/layout-animation-grow-repro:

1. Build and run the Fabric example app on Android.
2. Render the reproduction in EmptyExample.
3. Wait until the panel grows from 80 to 130 points during SlideInRight.
4. Tap the bottom of the green target, below the panel's original bottom edge.
5. Verify that the press counter increments.
6. Repeat with USE_ANIMATION_BACKEND disabled and enabled.

Validated on a Pixel 9 Pro Android API 36 emulator with both Layout Animations backends. In each case, a tap in the previously stale lower region incremented the counter from 0 to 1.

Checks run:

• yarn build-packages
• yarn workspace react-native-reanimated format:common --dry-run -Werror
• yarn workspace react-native-reanimated lint:apple
• yarn workspace react-native-reanimated lint:js
• yarn workspace react-native-reanimated type:check:src:native
• yarn workspace react-native-reanimated test --runInBand (1,556 tests)
• ./gradlew :app:assembleDebug -PreactNativeArchitectures=arm64-v8a --no-daemon with both Layout Animations backends

Changelog

• I added an entry to the Unpublished section of each changed package's CHANGELOG.md, or this PR does not change react-native-reanimated or react-native-worklets.

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📝 Walkthrough

Walkthrough

Updated legacy and experimental layout animation proxies to refresh ongoing animation targets from current ShadowView values. Revised experimental mutation handling to defer exiting animations, preserve animated subtrees, translate host indices, and flush dead nodes after light-tree updates. Added a changelog entry for stale entering-animation frames.

Merge Risk: 🟡 Moderate · up to 79a9d

The experimental layout-animation proxy can abort debug builds when deleting animated nodes and leak node entries in release builds because its deletion assertion conflicts with the animation lifecycle. This concrete runtime issue should be fixed before merging.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The proxy changes are in scope for #10161, but the changelog also documents breaking changes to animated refs and unmounted-ref measurement behavior that are not part of the linked issue or stated imp…	Remove the unrelated breaking-change changelog entries, or provide linked issue requirements and implementation evidence that justify them in this pull request.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary change: preserving layout updates during entering animations.
Description check	✅ Passed	The description directly explains the stale layout target issue, the legacy and experimental proxy fixes, and the validation performed.
Linked Issues check	✅ Passed	The implementation addresses issue #10161 by synchronizing ongoing animation targets with pass-through layout updates in both layout animation proxies, which preserves hit-testing geometry for visibly…

Full details: Linked Issues check

Explanation

The implementation addresses issue #10161 by synchronizing ongoing animation targets with pass-through layout updates in both layout animation proxies, which preserves hit-testing geometry for visibly expanded content.

Full details: Out of Scope Changes check

Explanation

The proxy changes are in scope for #10161, but the changelog also documents breaking changes to animated refs and unmounted-ref measurement behavior that are not part of the linked issue or stated implementation objective.

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[ngocdevv]

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

packages/react-native-reanimated/Common/cpp/reanimated/LayoutAnimations/LayoutAnimationsProxy_Experimental.cpp (1)

271-281: 🩺 Stability & Availability | 🟠 Major | ⚡ Quick win

Accept DELETED in the Delete case and erase the stale lightNodes_ entry.

Bruce found the real smoking gun here. startAnimationsRecursively marks removed descendants as DELETED and emits Remove followed by Delete, but it does not erase their lightNodes_ entries. The current Delete case rejects DELETED in debug builds and retains the entry in release builds.

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📒 Files selected for processing (3)

• packages/react-native-reanimated/CHANGELOG.md
• packages/react-native-reanimated/Common/cpp/reanimated/LayoutAnimations/LayoutAnimationsProxy_Experimental.cpp
• packages/react-native-reanimated/Common/cpp/reanimated/LayoutAnimations/LayoutAnimationsProxy_Experimental.h

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• packages/react-native-reanimated/CHANGELOG.md

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[ngocdevv]

Regarding the CodeRabbit outside-diff warning: the flagged Delete logic comes from upstream #10392 and is not part of this PR's final diff. React Native emits descendant Delete mutations before the removed subtree's root Remove, as described in #10392, so each entry is erased while its state is still UNDEFINED. startAnimationsRecursively later walks retained child shared pointers and may mark a now-detached node DELETED; there is no later original Delete for that node. The final diff against main remains limited to the five files for #10161, and the merged experimental proxy passed the arm64 Android C++ build.

[pawicao]

Thank you for this PR and the clear repro. Indeed the bug is confirmed, and your fix seems to have been addressing it well.

Note that these days we are working on some refactors of the layout animations proxy and the current rework in this matter addresses the issue as well (that refactor also caused all the conflicts that appeared in your PR afterwards). To be more specific #10373 is something we wish to land in the next release and its work includes the fix for the new refactored structure of the proxy as well.

I will therefore close this in favor of #10373 that supersedes this PR. Nevertheless, big thanks for your will of contribution. Cheers!