When --mypy-config-file is passed to stubtest is uses parse_config_file function. Which does not handle disable_error_code setting correctly. Since it is done in another place (mypy/main.py):

There are similar cases of options that are post-processed there, but not in parse_config_file, but let's fix them one by one to reduce potential regressions.

I propose adding process_error_codes method to Options object so it can be used in both main.py and stubtest.py (and others like stubgen in the future).

Found while working on python/typeshed#12463