[Compiler Bug]: `react-hooks/preserve-manual-memoization` is triggered for state setter depending on position of `useState`

[kachkaev]

What kind of issue is this?

• React Compiler core (the JS output is incorrect, or your app works incorrectly after optimization)
• babel-plugin-react-compiler (build issue installing or using the Babel plugin)
• eslint-plugin-react-compiler eslint-plugin-react-hooks (build issue installing or using the eslint plugin)
• react-compiler-healthcheck (build issue installing or using the healthcheck script)

Link to repro

https://playground.react.dev/#N4Igzg9grgTgxgUxALhASwLYAcIwC4AEAVAQIZgEBKCpchAZjBBgQDogw13sDcrAdgIQAPHPgL0o-Omgj8CAUWGlsAGwQAKYATwALNPwDmFAL4BKAsAEECcOWEJ6DhggF4d+o2AB09AwBMNJyM3AD4PZ29IDARgl3CABjM+QXlbe0IAbTspPAAaAjBYgGFofjwAXTcqLjxvKCKAZTxSPE0klOt0-gcCVVIAIwRVarjvfqHVbzwIABkIAHcEGGLyTWSurrsewl1Sfn91YtU0OABraupaOoaEVdVVAdozjS6bDQtXcKs0mxsivClXIaHLlMLpXIEADUBAAjBtfgQTHk3gRMhUUWkEV1OHhYPIADwDKB4GbyOTHU5nVzAPYHI4nc4mULACbDEzISygvAmAkAemJpLkoRSJhSIDyIG2fkMKHQ2FwjgAnlgEJYCAAFVRQQwGADyWDwsh6SIkTBYAHInpMALRYbW6-g2zjXG12bBodQwPn+NAOC2dfhaLp8vnurCe1rGgCyEH8CE57FID3YAhMhSjYD8CAoWp1+sNxrAyQl4F0iwAkuVlvxk2AUPQ6wgTEA

import * as React from "react";

export function Example({ things }) {
  const thing = things.find(thing => thing.something > 0);

  const [count, setCount] = React.useState(0);

  const label = thing.label.toLowerCase();
  
  const handleClick = React.useCallback(
    () => {
      setCount(count => count + 1);
    },
    [],
  );

  return <button onClick={handleClick}>{label}: {count}</button>;
};

Repro steps

1. Create a local state using useState() hook
2. Place it between two lines of code that contain chained method calls
3. Use state setter inside useCallback()

Expected: state setter does not need to be mentioned in useCallback deps

Observed:

Found 1 error:

Compilation Skipped: Existing memoization could not be preserved

React Compiler has skipped optimizing this component because the existing manual memoization could not
be preserved. The inferred dependencies did not match the manually specified dependencies, which could
cause the value to change more or less frequently than expected. The inferred dependency was `setCount`,
but the source dependencies were []. Inferred dependency not present in source.

---

Interestingly, the bug only occurs if useState is 'sandwiched' between two other lines. These lines need to be related to each other and contain .method() calls. Just getting object properties (e.g. thing.label instead of thing.label.toLowerCase()) is not enough to trigger the bug.

How often does this bug happen?

Every time

What version of React are you using?

19.2.0+ (inside playground.react.dev)

What version of React Compiler are you using?

1.0.0+ (inside playground.react.dev)

[KefeiQian]

Hi @kachkaev , I tried to reproduce the error in an empty react project, but it didn’t appear there — only in the playground. Could you help me reproduce the error?

https://github.com/KefeiQian/React-Debug/tree/34957

[kachkaev]

👋 @KefeiQian! Try eslint-plugin-react-hooks@7.0.1 instead of ^5.2.0.

[KefeiQian]

Tried, but no errors at all. @kachkaev Could you please clone my branch and see if I've missed smth?

https://github.com/KefeiQian/React-Debug/tree/34957

[kachkaev]

You need to run pnpm lint to see the error. You still have a hint on your screenshot though: Example component does not have ✨ next to it which means that it is not memoised by the compiler.

I fixed your eslint.config.js by replacing reactHooks.configs['recommended-latest'] with reactHooks.configs.flat['recommended-latest']. Then running pnpm lint revealed the error we see in the Playground:

/path/to/React-Debug/src/App.jsx
  14:5  error  Compilation Skipped: Existing memoization could not be preserved

React Compiler has skipped optimizing this component because the existing manual memoization could not
be preserved. The inferred dependencies did not match the manually specified dependencies, which could
cause the value to change more or less frequently than expected. The inferred dependency was `setCount`,
but the source dependencies were []. Inferred dependency not present in source.

  12 |
  13 |   const handleClick = useCallback(
> 14 |     () => {
     |     ^^^^^^^
> 15 |       setCount(count => count + 1);
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 16 |     },
     | ^^^^^^ Could not preserve existing manual memoization
  17 |     [],
  18 |   );
  19 |  react-hooks/preserve-manual-memoization