Stabilize reactFragments host node handle

[everettbu]

Mirror of facebook/react#35642
Original author: jackpope

---

react/react#34935 Introduced unstable_reactFragments handle on DOM nodes to enable caching of Observers.

This has been tested in production and is stable so it can be rolled out with the Fragment Refs feature.

[greptile-apps]

Greptile Summary

This PR stabilizes the reactFragments expando property on host nodes by removing the unstable_ prefix. The rename is applied across the DOM renderer, React Native Fabric renderer, and associated tests.

• Bug: Incomplete rename in DOM renderer's deleteChildFromFragmentInstance — The null-check on line 3605 of ReactFiberConfigDOM.js still references unstable_reactFragments while the property is now stored as reactFragments. This makes the delete call unreachable, causing fragment handles to never be cleaned up from DOM nodes (memory leak). The equivalent code in ReactFiberConfigFabric.js was renamed correctly.
• The Fabric renderer changes are clean and consistent.
• Tests were updated to use the new property name but do not cover the deleteChildFromFragmentInstance deletion path where the bug exists.

Confidence Score: 2/5

• This PR has an incomplete rename that introduces a memory leak in the DOM renderer's fragment cleanup path.
• The PR is a simple rename but has one missed occurrence of the old property name in a null-check, making the subsequent delete unreachable. This is a clear bug that causes fragment handles to never be removed from DOM nodes. The Fabric renderer was renamed correctly, confirming this is an oversight rather than intentional.
• Pay close attention to packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js — line 3605 still uses the old unstable_reactFragments name in a null-check, making the cleanup on line 3606 dead code.

Important Files Changed

Filename	Overview
packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js	Incomplete rename: deleteChildFromFragmentInstance still checks unstable_reactFragments (line 3605) but deletes from reactFragments (line 3606), making the delete unreachable and causing a memory leak.
packages/react-dom/src/tests/ReactDOMFragmentRefs-test.js	Test assertions correctly updated from unstable_reactFragments to reactFragments. No coverage for the deleteChildFromFragmentInstance code path, which is where the bug exists.
packages/react-native-renderer/src/ReactFiberConfigFabric.js	Clean, consistent rename of unstable_reactFragments to reactFragments across type definition, add, and delete paths. No issues found.

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Missed rename causes dead code / memory leak

The null-check on line 3605 still references the old property name unstable_reactFragments, but the property is now stored as reactFragments (set in addFragmentHandleToInstance). Since instance.unstable_reactFragments will always be undefined after this rename, the condition is never truthy, so reactFragments.delete(fragmentInstance) on line 3606 will never execute. This means fragment handles will accumulate on DOM nodes and never be cleaned up — a memory leak.

The Fabric renderer (ReactFiberConfigFabric.js:892) correctly renames both the check and the delete. This file should match:

Suggested change

	if (instance.unstable_reactFragments != null) {
	instance.unstable_reactFragments.delete(fragmentInstance);
	instance.reactFragments.delete(fragmentInstance);
	if (instance.reactFragments != null) {
	instance.reactFragments.delete(fragmentInstance);

Prompt To Fix With AI

This is a comment left during a code review.
Path: packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js
Line: 3605-3606

Comment:
**Missed rename causes dead code / memory leak**

The null-check on line 3605 still references the old property name `unstable_reactFragments`, but the property is now stored as `reactFragments` (set in `addFragmentHandleToInstance`). Since `instance.unstable_reactFragments` will always be `undefined` after this rename, the condition is never truthy, so `reactFragments.delete(fragmentInstance)` on line 3606 will never execute. This means fragment handles will accumulate on DOM nodes and never be cleaned up — a memory leak.

The Fabric renderer (`ReactFiberConfigFabric.js:892`) correctly renames both the check and the delete. This file should match:

```suggestion
    if (instance.reactFragments != null) {
      instance.reactFragments.delete(fragmentInstance);
```

How can I resolve this? If you propose a fix, please make it concise.

[everettbu]

Upstream PR was closed or merged. Code is synced via branch mirror.