compiler feature request: report error on reassigning a const

[HoikanChan]

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/#N4Igzg9grgTgxgUxALhAMygOzgFwJYSYAEAwhALYAOhCmOAFJTBJWAJRHAA6xRchYHEQDaADwA0RMAhwANALpEAvESjSAyjgCGOBPWBEAbloA2UBMiIByAIx2rRAL5sA3DyJ8BQwiQAWWzABzBGUiegQOJQA+TncPKRlZcIA6bRhgnGTjMwi3Xkc8jx9-IJCVekiYgwK4mBlYYno4jwAeKOb4lrxMSighbPMlYFEs03NHImKA4KGp0omAenbeeKIWvzwTABMiJY6Wvd5XHkcQRyA

Repro steps

assign to constant variable will be transformed(maybe cause SSA?)

  let onChange;
  let t1;

  if ($[1] === Symbol.for("react.memo_cache_sentinel")) {
    t1 = () => {};

    $[1] = t1;
  } else {
    t1 = $[1];
  }

Expect to throw the error.

How often does this bug happen?

Every time

What version of React are you using?

19.0.0-rc-81c5ff2e04-20240521

[josephsavona]

Thanks for posting. React Compiler is primarily focused on finding violations of React’s rules. We do detect a number of cases of incorrect JavaScript, but ultimately we’re assuming that developers are using something like ESLint and/or TypeScript if they want to find JS syntax/semantics bugs.

We could easily report an error in this case, and we’re open to feedback about whether that would be useful.