[compiler] Improved ref validation for non-mutating functions by josephsavona · Pull Request #35893 · facebook/react

josephsavona · 2026-02-24T17:22:46Z

If a function is known to freeze its inputs, and captures refs, then we can safely assume those refs are not mutated during render.

An example is React Native's PanResponder, which is designed for use in interaction handling. Calling PanResponder.create() creates an object that shouldn't be interacted with at render time, so we can treat it as freezing its arguments, returning a frozen value, and not accessing any refs in the callbacks passed to it. ValidateNoRefAccessInRender is updated accordingly - if we see a Freeze and ImmutableCapture for the same place in the same instruction, we know that it's not being mutated.

Note that this is a pretty targeted fix. One weakness is that we may not always emit a Freeze effect if a value is already frozen, which could cause this optimization not to kick in. The worst case there is that you'd just get a ref access in render error though, not miscompilation. And we could always choose to always emit Freeze effects, even for frozen values, just to retain the information for validations like this.

josephsavona · 2026-02-24T17:23:50Z

cc @lunaleaps

josephsavona · 2026-02-24T17:24:38Z

+
 function Foo(props, ref) {
-  console.log(ref.current);
+  mutate(ref.current);


console.log() was a bad example here since it's a function we know doesn't mutate it's arguments, so changing to one that might

If a function is known to freeze its inputs, and captures refs, then we can safely assume those refs are not mutated during render. An example is React Native's PanResponder, which is designed for use in interaction handling. Calling `PanResponder.create()` creates an object that shouldn't be interacted with at render time, so we can treat it as freezing its arguments, returning a frozen value, and not accessing any refs in the callbacks passed to it. ValidateNoRefAccessInRender is updated accordingly - if we see a Freeze <place> and ImmutableCapture <place> for the same place in the same instruction, we know that it's not being mutated. Note that this is a pretty targeted fix. One weakness is that we may not always emit a Freeze effect if a value is already frozen, which could cause this optimization not to kick in. The worst case there is that you'd just get a ref access in render error though, not miscompilation. And we could always choose to always emit Freeze effects, even for frozen values, just to retain the information for validations like this.

mofeiZ

Makes sense! Thanks for the thorough comments and PR summary.

We probably already do this in other places, but it took a while to wrap my head around using Frozen to describe internally mutable values that aren't accessed during render. This is a pretty different use-case of Frozen from hook and jsx captures, but it makes sense. This transfers ownership to non-render code, and it has retains the same reordering / observability properties (all references after the Freeze should be reorderable, since the references should be happening in non-render code anyways)

If a function is known to freeze its inputs, and captures refs, then we can safely assume those refs are not mutated during render. An example is React Native's PanResponder, which is designed for use in interaction handling. Calling `PanResponder.create()` creates an object that shouldn't be interacted with at render time, so we can treat it as freezing its arguments, returning a frozen value, and not accessing any refs in the callbacks passed to it. ValidateNoRefAccessInRender is updated accordingly - if we see a Freeze <place> and ImmutableCapture <place> for the same place in the same instruction, we know that it's not being mutated. Note that this is a pretty targeted fix. One weakness is that we may not always emit a Freeze effect if a value is already frozen, which could cause this optimization not to kick in. The worst case there is that you'd just get a ref access in render error though, not miscompilation. And we could always choose to always emit Freeze effects, even for frozen values, just to retain the information for validations like this. DiffTrain build for [e33071c](e33071c)

…ok#35893) If a function is known to freeze its inputs, and captures refs, then we can safely assume those refs are not mutated during render. An example is React Native's PanResponder, which is designed for use in interaction handling. Calling `PanResponder.create()` creates an object that shouldn't be interacted with at render time, so we can treat it as freezing its arguments, returning a frozen value, and not accessing any refs in the callbacks passed to it. ValidateNoRefAccessInRender is updated accordingly - if we see a Freeze <place> and ImmutableCapture <place> for the same place in the same instruction, we know that it's not being mutated. Note that this is a pretty targeted fix. One weakness is that we may not always emit a Freeze effect if a value is already frozen, which could cause this optimization not to kick in. The worst case there is that you'd just get a ref access in render error though, not miscompilation. And we could always choose to always emit Freeze effects, even for frozen values, just to retain the information for validations like this. DiffTrain build for [e33071c](facebook@e33071c)

This MR contains the following updates: | Package | Type | Update | Change | OpenSSF | |---|---|---|---|---| | [@typescript-eslint/eslint-plugin](https://typescript-eslint.io/packages/eslint-plugin) ([source](https://github.com/typescript-eslint/typescript-eslint/tree/HEAD/packages/eslint-plugin)) | devDependencies | minor | [`8.58.2` → `8.59.0`](https://renovatebot.com/diffs/npm/@typescript-eslint%2feslint-plugin/8.58.2/8.59.0) | [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/typescript-eslint/typescript-eslint/badge)](https://securityscorecards.dev/viewer/?uri=github.com/typescript-eslint/typescript-eslint) | | [@typescript-eslint/parser](https://typescript-eslint.io/packages/parser) ([source](https://github.com/typescript-eslint/typescript-eslint/tree/HEAD/packages/parser)) | devDependencies | minor | [`8.58.2` → `8.59.0`](https://renovatebot.com/diffs/npm/@typescript-eslint%2fparser/8.58.2/8.59.0) | [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/typescript-eslint/typescript-eslint/badge)](https://securityscorecards.dev/viewer/?uri=github.com/typescript-eslint/typescript-eslint) | | [ajv](https://ajv.js.org) ([source](https://github.com/ajv-validator/ajv)) | dependencies | minor | [`8.18.0` → `8.20.0`](https://renovatebot.com/diffs/npm/ajv/8.18.0/8.20.0) | [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/ajv-validator/ajv/badge)](https://securityscorecards.dev/viewer/?uri=github.com/ajv-validator/ajv) | | [eslint-plugin-react-hooks](https://react.dev/) ([source](https://github.com/facebook/react/tree/HEAD/packages/eslint-plugin-react-hooks)) | devDependencies | minor | [`7.0.1` → `7.1.1`](https://renovatebot.com/diffs/npm/eslint-plugin-react-hooks/7.0.1/7.1.1) | [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/facebook/react/badge)](https://securityscorecards.dev/viewer/?uri=github.com/facebook/react) | | [react-toastify](https://github.com/fkhadra/react-toastify) | dependencies | minor | [`11.0.5` → `11.1.0`](https://renovatebot.com/diffs/npm/react-toastify/11.0.5/11.1.0) | [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/fkhadra/react-toastify/badge)](https://securityscorecards.dev/viewer/?uri=github.com/fkhadra/react-toastify) | | [typescript-eslint](https://typescript-eslint.io/packages/typescript-eslint) ([source](https://github.com/typescript-eslint/typescript-eslint/tree/HEAD/packages/typescript-eslint)) | devDependencies | minor | [`8.58.2` → `8.59.0`](https://renovatebot.com/diffs/npm/typescript-eslint/8.58.2/8.59.0) | [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/typescript-eslint/typescript-eslint/badge)](https://securityscorecards.dev/viewer/?uri=github.com/typescript-eslint/typescript-eslint) | | [vite-plugin-static-copy](https://github.com/sapphi-red/vite-plugin-static-copy) | devDependencies | minor | [`4.0.1` → `4.1.0`](https://renovatebot.com/diffs/npm/vite-plugin-static-copy/4.0.1/4.1.0) | [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/sapphi-red/vite-plugin-static-copy/badge)](https://securityscorecards.dev/viewer/?uri=github.com/sapphi-red/vite-plugin-static-copy) | --- ### Release Notes <details> <summary>typescript-eslint/typescript-eslint (@typescript-eslint/eslint-plugin)</summary> ### [`v8.59.0`](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8590-2026-04-20) [Compare Source](typescript-eslint/typescript-eslint@v8.58.2...v8.59.0) ##### 🚀 Features - **eslint-plugin:** \[no-unnecessary-type-assertion] report more cases based on assignability ([#11789](typescript-eslint/typescript-eslint#11789)) ##### ❤️ Thank You - Ulrich Stark See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.59.0) for more information. 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([@jorge-cab](https://github.com/jorge-cab) in [#35691](facebook/react#35691)) - Fix `useEffectEvent` checks in component syntax. ([@jbrown215](https://github.com/jbrown215) in [#35041](facebook/react#35041)) - Improved `set-state-in-effect` validation with fewer false negatives. ([@jorge-cab](https://github.com/jorge-cab) in [#35134](facebook/react#35134), [@josephsavona](https://github.com/josephsavona) in [#35147](facebook/react#35147), [@jackpope](https://github.com/jackpope) in [#35214](facebook/react#35214), [@chesnokov-tony](https://github.com/chesnokov-tony) in [#35419](facebook/react#35419), [@jsleitor](https://github.com/jsleitor) in [#36107](facebook/react#36107)) - Improved ref validation for non-mutating functions and event handler props. 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Rename functions can now return `{ name, stripBase }` objects instead of only strings, making it easier to declaratively control output paths from dynamic rename logic. ```js // node_modules/lib/dist/index.js → vendor/lib.js { src: 'node_modules/lib/dist/index.js', dest: 'vendor', rename: { name: 'lib.js', stripBase: true } } // src/pages/events/test.html → dist/events/index.html { src: 'src/pages/**/*.html', dest: 'dist/', rename: { stripBase: 2, name: 'index.html' } } ``` </details> --- - [ ] If you want to rebase/retry this MR, check this box --- This MR has been generated by [Mend Renovate](https://github.com/renovatebot/renovate).  See merge request swiss-armed-forces/cyber-command/cea/loom!480 Co-authored-by: Loom MR Pipeline Trigger <group_103951964_bot_9504bb8dead6d4e406ad817a607f24be@noreply.gitlab.com>

meta-cla Bot added the CLA Signed label Feb 24, 2026

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josephsavona commented Feb 24, 2026

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josephsavona force-pushed the pr35893 branch from 62feadf to db77ad9 Compare February 24, 2026 17:38

josephsavona requested review from mofeiZ and mvitousek February 24, 2026 17:39

josephsavona force-pushed the pr35893 branch from db77ad9 to 5570223 Compare February 24, 2026 17:47

mofeiZ approved these changes Feb 24, 2026

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josephsavona merged commit e33071c into main Feb 24, 2026
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Upgrade React from c0060cf2-20260224 to e33071c6-20260224 vercel/next.js#90529

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[compiler] Improved ref validation for non-mutating functions#35893

[compiler] Improved ref validation for non-mutating functions#35893
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