This specific problem is not a deal breaker in practice. You solve the problem by adding to the readme of the tool "If the arity of a function cannot be established, we assume no arguments and print an warning. Add {foobar} before the function to assume arguments. Sorry for inconvenience."
No language tooling is perfect. We shouldn't expect that from Perl tooling either.
No language tooling is perfect. We shouldn't expect that from Perl tooling either.