[Compiler Bug]: "Mutating a value returned from 'useContext()', which should not be mutated" When the value is a Ref

[jay-herrera]

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/#N4Igzg9grgTgxgUxALhAgHgBwjALgAjggDswCBZATwGETcMCBeQmBAQ3tuPvVwApgAHWKCebALaYANggBKCAGbJ8wOLFbdlxKFKkBfYXoCUw4Rmx58AE0VsdBBVGJxcASxL4ACmw25akkgRuPiMVYXxCEjJ8DAlpOUV8ZigwBIU+AHIAOQgMkxFiCNZcWEK+cIj8AB4APgrK6qouHlwAOk8YCAA3VxsYfC62KSgERmBgWMkZeQU9PTrChsqq6gALVykrf2xiIIIAegWl6v2mugZ2zp6+o+XDiqMAbkNTYkdnNw81ja2IAN3gqEhIsiKQCMAYug4tNEnokvgUghmgw+GduAx8hVEQBRBQKBAuPghJI1MKLCKTeIzVpqGC+eEZACaCDAGQqegANPgANqUmEKAC6+QiFWKpWqVlcXXuxAMxBAeiAA

Repro steps

1. Instantiate a Context
2. In Parent, Instantiate a ref
3. Wrap the child in the Context's Provider, and pass the ref as a value
4. Get the ref in the child, and mutate it in a useEffect

How often does this bug happen?

Every time

What version of React are you using?

18.3.1

What version of React Compiler are you using?

19.0.0-beta-63b359f-20241101

[jay-herrera]

Also applies to Event Handlers:
https://playground.react.dev/#N4Igzg9grgTgxgUxALhAgHgBwjALgAjggDswCBZATwGETcMCBeQmBAQ3tuPvVwApgAHWKCebALaYANggBKCAGbJ8wOLFbdlxKFKkBfYXoCUw4Rmx58AE0VsdBBVGJxcASxL4ACmw25akkgRuPiMVYXxCEjJ8DAlpOUV8ZigwBIU+AHIAOQgMkxFiCNZcWEK+cIj8AB4APgrK6qouHlwAOk8YCAA3VxsYfC62KSgERmBgWMkZeQU9PTrChsqq6gALVykrf2xiIIIAegWl6v2mugZ2zp6+o+XDiqMAbkNTYkdnNw81ja2IAN3gqEhIsiKQCMAYug4tNEnokvgUghmgw+GduAx8hViqVqlZXF18CRqFJXHAANZjEJJGphRYRSbxGatNQwXzwjIATQQYAyFTm+HuxAMxBAeiAA

[Vansh16aug]

I see , i would like to work on it

[jay-herrera]

@Vansh16aug Hey! any updates?

[salomonme]

Hey! any updates?

[josephsavona]

#34005 enables the flag to treat ref-like identifiers as refs by default. As long as your variable is named ref or ends in Ref (myRef etc), the compiler will treat it as a ref. Thanks again for posting!