[Compiler Bug]: Increment expression in for-loop loses assignment operation

[derekcicerone]

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/#N4Igzg9grgTgxgUxALhAMygOzgFwJYSYAEAGgBQCURwAOsUWhDEWQDYI5F5EC8RADAG4uRADxEAjPyEi+3ANSSqwAL50VIFUA

Repro steps

In our repo we have code similar to the Playground link posted above which when compiled loses the assignment part of the increment expression.

The original code:

          for (
            let node: LexicalNode | null = selection.anchor.getNode();
            node && !$isRootNode(node);
            node = node.getParent()
          ) {

Compiled to this code:

        for (let node5 = selection.anchor.getNode(); node5 && !$isRootNode2(node5); node5.getParent()) {

Happy to provide additional information or context if needed, thanks!

How often does this bug happen?

Every time

What version of React are you using?

19.0.0-rc-f3e09d6328-20240612

[josephsavona]

Thanks for the bug report, we’ll take a look!

[Fnll]

It seams that updateValue in for loop will be reassigned to LoadLocal even if it is originally a StoreLocal Reassign instruction at here.

can we simply use the original instruction's value just like how it's tackled for while loop at here?

[josephsavona]

Fix landed, thanks for filing!

[derekcicerone]

Thanks, that was quick!