Rather than writing a custom parser, what if the profiles were just Python code

def load_profile(profile_file):
  profile_globals = {"test_dirs": set(), "exclude_tests: set() }
  exec(profile_file, profile_globals)
  return profile_globals["test_dirs"], profile_globals["exclude_tests"]

This would allow you to write either:

test_dirs.add(...)

or

test_dirs = ...

in the profile script.

I'm just not really fond of exec myself, but your approach in this case makes more sense if test_dirs and exclude_tests are pre-populated with the default lists. This way one may not only add new entries but delete ones that aren't relevant for a particular port (or add conditional exclusions if some environment variables set by make are passed down to the configuration script, like the board name for instance).

Also, if the global test_dirs and exclude_tests variables are filtered through the configuration script rather than composed from the configuration script output it also resolves the nomenclature remark. The global variables get reassigned from the output of load_profile so no new variables are defined.

Ok, I've switched to a Python script as a configuration file. I wonder whether I should change the configuration script extension to .py and let ruff skip error F821 on that file as well in pyproject.toml (or maybe use ports/**/tests_profile.py?)

I think it's fine to leave it as a .txt.