Flow thinks "arguments" is an array?

[olleharstedt]

Flow version: 0.137.0

Expected behavior

arguments is not exactly an array, and does not have function forEach.

Actual behavior

No warning for the following code:

function foo() {
  arguments.forEach(() => {
  });
}

• Link to Try-Flow or Github repo: https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoVUCuA7AxgFwEs5swo44AKQgGjACs6BrASjAG9UwwBDAJwDmmALYBTbPgDOAOnJ8Aoj1wALSpTYBeAHwcuYAL4sA3Kn1A

[Brianzchen]

Actually it's set to explicit any. You can do anything with it https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoVUCuA7AxgFwEs5swo44AKQgGjACs6BrASjAG9UwwBDAJwDmmALYBTbPgDOAOgGj8AWVEBlOGIBq-Si1QBfIA

[olleharstedt]

Oh, OK. Can this be fixed to be more specific?

[Brianzchen]

It's defined here if you think it can be refined https://github.com/facebook/flow/blob/master/lib/core.js#L345

[olleharstedt]

This is the ts declaration:

interface IArguments {
    [index: number]: any;
    length: number;
    callee: Function;
}

Can it easily be translated to Flow?

https://github.com/microsoft/TypeScript/blob/master/lib/lib.es5.d.ts#L388-L392

[Brianzchen]

Maybe something like this?

Maybe you can first change the core.js locally to see if it works better, and then maybe check with others on discord to see if it's appropriate to make this change. I think this works but I'm not confident 😅

[olleharstedt]

Yeah, I can check. Thanks!