Unused imports, arguments, variables

[ZedThree]

I think this is mostly just a case of checking identifiers in the current scope, but some care might be needed so we don't get any false positives.

[LiamPattinson]

I have some performance concerns here, as checking the entire file for each import could be very costly. Would it be possible to do a first pass of the file, log which variables appear in each scope, and then reference that during the check? This would also allow us to flag unknown variables quite easily.

[ZedThree]

Yep, I was thinking something like that would allow us to do other checks too. Ruff basically does something similar for their import checking: https://docs.astral.sh/ruff/contributing/#compilation-pipeline