Changes

Fixes #550

check_signature_compatible in src/typeguard/_checkers.py calls .pop(0) on protocol_args and subject_args to strip the implicit self, but does so unconditionally whenever the corresponding side is classified as "instance". If the subject method's inspect.signature(...) reports zero positional-or-keyword parameters and no *args (e.g. a callable instance assigned at class scope, a functools.partial with all positional args bound, or a method proxied by a code-generation framework), subject_args is empty and pop(0) raises IndexError instead of letting the function fall through to its existing zip_longest comparison and emit a TypeCheckError.

This guards each pop with a non-empty check. After the change, the previously-crashing input raises TypeCheckError("... has too few positional arguments") along the same path as the equivalent N → N-1 mismatch with one more arg, restoring check_type's documented contract that callers can catch via except TypeCheckError.

Regression test added under tests/test_checkers.py::TestProtocol::test_subject_method_no_positional_params.

Checklist

If this is a user-facing code change, like a bugfix or a new feature, please ensure that
you've fulfilled the following conditions (where applicable):

• You've added tests (in tests/) added which would fail without your patch
• You've updated the documentation (in docs/, in case of behavior changes or new
  features)
• You've added a new changelog entry (in docs/versionhistory.rst).

If this is a trivial change, like a typo fix or a code reformatting, then you can ignore
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Updating the changelog

• Fixed crash in protocol check when subject method has no positional params (#550 <https://github.com/agronholm/typeguard/issues/550>_; PR by @HackedRico)