fix(react): clear removed snapshot prop refs by Yradex · Pull Request #2590 · lynx-family/lynx-stack

Yradex · 2026-05-09T12:09:06Z

Summary by CodeRabbit

Bug Fixes
- Cleared transient snapshot child property references when snapshot subtrees are removed, preventing deleted items from being retained.
Tests
- Added tests covering cleanup behavior for removed children, including nested arrays and cyclic reference scenarios.

Summary

This fixes a main-thread snapshot retention path where removed child subtrees could still be strongly referenced by compiler-generated transient child props. Snapshot JSX uses $* props as staging references for named children; when SnapshotInstance.removeChild() detached a child, the structural tree and native elements were cleaned up, but those $* props could still point at the removed snapshot subtree.

The practical failure mode is that a deleted list holder or list item subtree can remain reachable from the root props chain after it is removed. That keeps old snapshot instances alive even though they are no longer part of the rendered tree.

Key points

Clear transient $* owner props during removal. Direct refs such as { $0: removedChild } are deleted from props, so the owner no longer keeps a hard reference to the removed subtree after removeChild().
Handle compiled array child shapes recursively. When a transient prop stores children as arrays, only removed snapshot entries are cleared, including nested arrays:
```
// before removal
owner.props.$0 = [keptChild, [removedChild]];

// after removeChild(removedChild)
owner.props.$0 = [keptChild, [undefined]];
```
Clean transient props inside the removed subtree as it is torn down. This breaks references held by the deleted subtree itself, including component/list structures that had their own compiled child staging props.

Runtime Contract

This only affects compiler-owned transient child props whose keys start with $. Normal user props, public runtime APIs, serialized snapshot shape, native patch operations, and list update protocols are unchanged.

The cleanup is tied to SnapshotInstance.removeChild(): removed snapshot instances and descendants are collected into a removal set, then $* prop values are cleared if they directly reference any removed snapshot or contain one inside an array. Existing array identity is preserved, and non-removed entries keep their current identity and order.

Checklist

Tests updated (or not required).
Documentation updated (or not required).
Changeset added, and when a BREAKING CHANGE occurs, it needs to be clearly marked (or not required).

changeset-bot · 2026-05-09T12:09:11Z

🦋 Changeset detected

Latest commit: 3ebe048

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@lynx-js/react	Patch
@lynx-js/react-umd	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

coderabbitai · 2026-05-09T12:09:14Z

📝 Walkthrough

Walkthrough

Adds helpers to find removed snapshot nodes and clears compiler-transient $* child prop refs during SnapshotInstance.removeChild traversal (before list-holder logic and while visiting subtree nodes). Adds tests and a changeset note documenting the behavior.

Changes

Transient child prop cleanup on snapshot removal

Layer / File(s)	Summary
Cleanup helpers and removeChild integration `packages/react/runtime/src/snapshot/snapshot/snapshot.ts`	Helper functions detect removed snapshot instances and clear transient `$*` props; `removeChild` computes the removed set and invokes clearing before list-holder logic and during both list-holder and non-list-holder subtree traversals.
Test coverage for transient cleanup `packages/react/runtime/__test__/snapshot/renderToOpcodes.test.jsx`	Adds four tests validating single and nested transient `$` prop clearing, multiple named `$` keys being cleared, and cyclic transient-array tolerance; updates `renderOpcodesInto` expectations for cleared vnodes.
Changeset documentation `.changeset/clear-snapshot-prop-refs.md`	Patch release note documenting that transient snapshot child props are cleared on subtree detachment to avoid stale compiled `$*` references.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

lynx-family/lynx-stack#2041: Modifies subtree removal timing for snapshotDestroyList, touching the same removal traversal where transient prop cleanup is added.
lynx-family/lynx-stack#2393: Adds removeChildren and refactors removal paths in the snapshot runtime; the new cleanup should apply to that bulk-removal path.

Suggested reviewers

HuJean
hzy

Poem

🐰 I hopped through props both near and far,

Found $N traces clinging like a burr,
With gentle nibble and tidy sweep,
I cleared the ghosts so trees can sleep,
Now snapshots hop on, light and sure.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix(react): clear removed snapshot prop refs' directly and accurately reflects the main objective of the PR: fixing a snapshot retention bug by clearing transient `$*` props that reference removed snapshots.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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codecov · 2026-05-09T12:11:42Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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codspeed-hq · 2026-05-09T12:44:02Z

Merging this PR will degrade performance by 21.72%

⚠️

Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 2 regressed benchmarks
✅ 79 untouched benchmarks
⏩ 26 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	`BASE`	`HEAD`	Efficiency
❌	`002-hello-reactLynx-destroyBackground`	670.3 µs	916.9 µs	-26.9%
❌	`008-many-use-state-destroyBackground`	8 ms	9.5 ms	-16.17%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

_{Comparing Yradex:wt/run-on-background-clear-prop-refs (3ebe048) with main (66f6ecf)}

26 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

relativeci · 2026-05-09T12:44:03Z

React External

#1321 Bundle Size — 695.33KiB (+0.33%).

3ebe048(current) vs 66f6ecf main#1314(baseline)

Bundle metrics

1 change

	Current #1321	Baseline #1314
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	Current #1321	Baseline #1314
Other	`695.33KiB` (`+0.33%`)	`693.04KiB`

Bundle analysis report Branch Yradex:wt/run-on-background-clea... Project dashboard

^{Generated by RelativeCI Documentation Report issue}

relativeci · 2026-05-09T12:44:03Z

React Example with Element Template

#473 Bundle Size — 199.83KiB (0%).

3ebe048(current) vs 66f6ecf main#466(baseline)

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1 change

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Bundle analysis report Branch Yradex:wt/run-on-background-clea... Project dashboard

^{Generated by RelativeCI Documentation Report issue}

relativeci · 2026-05-09T12:44:03Z

Web Explorer

#9781 Bundle Size — 901.38KiB (0%).

3ebe048(current) vs 66f6ecf main#9775(baseline)

Bundle metrics

2 changes

	Current #9781	Baseline #9775
Initial JS	`45.06KiB`	`45.06KiB`
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Duplicate Code	`27.23%`(`+0.04%`)	`27.22%`
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Bundle size by type no changes

	Current #9781	Baseline #9775
JS	`497.1KiB`	`497.1KiB`
Other	`402.06KiB`	`402.06KiB`
CSS	`2.22KiB`	`2.22KiB`

Bundle analysis report Branch Yradex:wt/run-on-background-clea... Project dashboard

^{Generated by RelativeCI Documentation Report issue}

relativeci · 2026-05-09T12:44:04Z

React MTF Example

#1340 Bundle Size — 208.1KiB (+0.31%).

3ebe048(current) vs 66f6ecf main#1333(baseline)

Bundle metrics

2 changes

	Current #1340	Baseline #1333
Initial JS	`0B`	`0B`
Initial CSS	`0B`	`0B`
Cache Invalidation	`46.38%`	`0%`
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Bundle size by type

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	Current #1340	Baseline #1333
IMG	`111.23KiB`	`111.23KiB`
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Bundle analysis report Branch Yradex:wt/run-on-background-clea... Project dashboard

^{Generated by RelativeCI Documentation Report issue}

relativeci · 2026-05-09T12:44:06Z

React Example

#8207 Bundle Size — 237.15KiB (+0.27%).

3ebe048(current) vs 66f6ecf main#8200(baseline)

Bundle metrics

2 changes

	Current #8207	Baseline #8200
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	Current #8207	Baseline #8200
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Bundle analysis report Branch Yradex:wt/run-on-background-clea... Project dashboard

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chatgpt-codex-connector · 2026-05-12T06:34:16Z

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/react/runtime/src/snapshot/snapshot/snapshot.ts`:
- Around line 74-83: clearTransientChildPropRefs currently retraverses the
removed subtree via traverseSnapshotInstance, causing O(n²) behavior when
callers repeatedly call clearTransientChildPropRefs(v, v); refactor to accept a
precomputed WeakSet of removed snapshots (e.g., add an optional parameter
removedSnapshots: WeakSet<object>) or an overload so callers can compute
removedSnapshots once using traverseSnapshotInstance(removedChild, ...) and pass
it in; update clearTransientChildPropRefs(owner, removedChild,
removedSnapshots?) to use the passed set if present (fall back to current
traversal only if not provided) and change the current call sites that do
clearTransientChildPropRefs(v, v) to compute the removedSnapshots once and pass
it in, preserving existing behavior when not provided.

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📒 Files selected for processing (3)

.changeset/clear-snapshot-prop-refs.md
packages/react/runtime/__test__/snapshot/renderToOpcodes.test.jsx
packages/react/runtime/src/snapshot/snapshot/snapshot.ts

coderabbitai

🧹 Nitpick comments (1)

packages/react/runtime/__test__/snapshot/renderToOpcodes.test.jsx (1)
111-122: 💤 Low value

Consider testing deeper nesting levels.

The test verifies 2-level nesting ([[child]]), which is good. Since the PR description mentions recursive handling of array shapes, consider adding a test case with 3+ levels of nesting (e.g., [[[child]]]) to more thoroughly verify the recursive cleanup logic handles arbitrary depth.
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/react/runtime/__test__/snapshot/renderToOpcodes.test.jsx` around
lines 111 - 122, Add a parallel test that exercises deeper nesting (e.g., use
createElement('view', { $0: [[[child]]] }) and run renderToString(vnode, new
SnapshotInstance('root'))), then call vnode.removeChild(child) and assert that
vnode.props.$0 becomes the same shape with the child replaced by undefined
(e.g., [[[undefined]]]) and vnode.childNodes is empty; mimic the existing test
block ("should clear removed children from nested transient prop arrays") but
with three or more nested array levels to verify recursive cleanup in
removeChild and the transient-props handling.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@packages/react/runtime/__test__/snapshot/renderToOpcodes.test.jsx`:
- Around line 111-122: Add a parallel test that exercises deeper nesting (e.g.,
use createElement('view', { $0: [[[child]]] }) and run renderToString(vnode, new
SnapshotInstance('root'))), then call vnode.removeChild(child) and assert that
vnode.props.$0 becomes the same shape with the child replaced by undefined
(e.g., [[[undefined]]]) and vnode.childNodes is empty; mimic the existing test
block ("should clear removed children from nested transient prop arrays") but
with three or more nested array levels to verify recursive cleanup in
removeChild and the transient-props handling.

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📒 Files selected for processing (2)

packages/react/runtime/__test__/snapshot/renderToOpcodes.test.jsx
packages/react/runtime/src/snapshot/snapshot/snapshot.ts

🚧 Files skipped from review as they are similar to previous changes (1)

packages/react/runtime/src/snapshot/snapshot/snapshot.ts

fix(react): clear removed snapshot prop refs

2354303

Yradex force-pushed the wt/run-on-background-clear-prop-refs branch from d81fa3c to 2354303 Compare May 9, 2026 14:07

Yradex marked this pull request as ready for review May 12, 2026 06:34

Yradex requested review from HuJean and hzy as code owners May 12, 2026 06:34

coderabbitai Bot added the framework:React label May 12, 2026

coderabbitai Bot reviewed May 12, 2026

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Comment thread packages/react/runtime/src/snapshot/snapshot/snapshot.ts Outdated

upupming reviewed May 12, 2026

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Comment thread packages/react/runtime/src/snapshot/snapshot/snapshot.ts Outdated

fix(react): align transient snapshot prop cleanup

3ebe048

coderabbitai Bot reviewed May 14, 2026

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upupming approved these changes May 14, 2026

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HuJean approved these changes May 14, 2026

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Yradex merged commit d182a06 into lynx-family:main May 14, 2026
80 of 85 checks passed

Yradex deleted the wt/run-on-background-clear-prop-refs branch May 14, 2026 12:47

github-actions Bot mentioned this pull request May 14, 2026

chore: Release 2026-05-15 12:19:18 #2535

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Summary by CodeRabbit

Summary

Key points

Runtime Contract

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Walkthrough

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