[Compiler Bug]: False positive local mutation warning inside filter

[gaearon]

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 (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/#N4Igzg9grgTgxgUxALhASwLYAcIwC4AEASggIZyEBmMEGBA5DGRfQDoB2HCAHjvgZSjsKaCOwIBhWjnYJ2eABTA0eBBjABfAJQFgHAgThiwhE1EqUCAXmLM8AOihgEAWTUQFCnVYB8u-QYEADYIhGhgUhBB1gKkQc4BBkbsJgSQGAgAkqrqMSpqYImB9pRoQaowCnCkTgjWfnrigc1ollU1ziUQEDqNzf0E4ZHRNngwUAhFzRpTgUx4sOJjE7PaHEWtBArpWTlg9iHsAOZ4ABYEfgAMvbPzi7o72QUANIMR3UEzTQZfP68A2vl1ABdLQBO4wcQAHgAJmgAG4EAD0Pg4XxAGiAA

Repro steps

import React from 'react'

export function Component({items}) {
  const stuff = React.useMemo(() => {
    let isCool = false
    const someItems = items
      .filter(cause => {
        if (cause.foo) {
          isCool = true
        }
        return true
      })

    if (someItems.length > 0) {
      return {someItems, isCool}
    }
  }, [items])
  return <div />
}

Getting:

InvalidReact: Reassigning a variable after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead. Variable `isCool` cannot be reassigned after render (9:9)

But it's not used after render. Curiously, changing the if condition to something that doesn't refer to someItems helps.

How often does this bug happen?

Every time

What version of React are you using?

18.2.0

What version of React Compiler are you using?

19.0.0-beta-a7bf2bd-20241110

[josephsavona]

Thanks for reporting, definitely a bug.