Add a rule to point out unused variables

[milancermak]

Amarna already lovingly warns about unused imports, function call arguments or functions themselves. Can you add a rule to warn about unused variables to its arsenal as well?

Example:

func foo{syscall_ptr : felt*, pedersen_ptr : HashBuiltin*, range_check_ptr}() -> (val):
    let (caller) = get_caller_address()
    return (42)
end

In the above example, caller is never used. The rule would point it out.

[fcasal]

Hi @milancermak, Amarna already finds this with the dead-store rule: there was a value saved in caller but never used before a return statement:

Let me know if there are examples where you don't see this being found!

[milancermak]

Ah, you're right. I even though I saw it before but whilst doing code review on a PR, I've noticed an unused variable but no Amarna warning attached (link if you're curious, line 131 in Food.cairo). It probably has something to do with the GitHub action, because when I run amarna locally on the file, it does catch it. Sorry for the false alarm 🙏