pants mypy checks doesn't follow exclude

[Adityav2410]

I have a repository configured with pants, and i want to exclude _test.py files from mypy/type checks.
I have tried multiple combinations/ways to provide exclude but none of them seems to work with pants.

Here are few of my attempts:

1. Provide exclude in mypy.ini file
   [mypy] exclude = _test\.py$
   If i run mypy src/, mypy excludes my test files. But pants check :: runs on my test files. pants check however respects other flags provided in my mypy.ini file though, like follow_imports.

2. Provide exclude in CLI argument
   a. mypy --exclude '_test\.py$' src/ This works fine as I expect. test files are excluded.
   b. ` pants -ldebug --print-stacktrace check --mypy-args "--exclude '_test.py$'" ::

Unknown flag --exclude '_test\.py$' on check scope
Use `pants help check` to get help.
10:27:07.01 [ERROR] Unknown flags --exclude '_test\.py$' on scope check
Traceback (most recent call last):
  File "/Users/aditya/Library/Caches/nce/fc197caf7591487de8182f7932e70c61b197372bb3ec4c3ed53f6a8feac3234f/bindings/venvs/2.16.0/lib/python3.9/site-packages/pants/bin/daemon_pants_runner.py", line 131, in single_daemonized_run
    runner = LocalPantsRunner.create(
  File "/Users/aditya/Library/Caches/nce/fc197caf7591487de8182f7932e70c61b197372bb3ec4c3ed53f6a8feac3234f/bindings/venvs/2.16.0/lib/python3.9/site-packages/pants/bin/local_pants_runner.py", line 106, in create
    options.for_scope(scope)
  File "/Users/aditya/Library/Caches/nce/fc197caf7591487de8182f7932e70c61b197372bb3ec4c3ed53f6a8feac3234f/bindings/venvs/2.16.0/lib/python3.9/site-packages/pants/util/memo.py", line 123, in memoize
    result = func(*args, **kwargs)
  File "/Users/aditya/Library/Caches/nce/fc197caf7591487de8182f7932e70c61b197372bb3ec4c3ed53f6a8feac3234f/bindings/venvs/2.16.0/lib/python3.9/site-packages/pants/option/options.py", line 350, in for_scope
    values = self.get_parser(scope).parse_args(parse_args_request)
  File "/Users/aditya/Library/Caches/nce/fc197caf7591487de8182f7932e70c61b197372bb3ec4c3ed53f6a8feac3234f/bindings/venvs/2.16.0/lib/python3.9/site-packages/pants/option/parser.py", line 289, in parse_args
    raise UnknownFlagsError(tuple(flag_value_map.keys()), self.scope)
pants.option.errors.UnknownFlagsError: Unknown flags --exclude '_test\.py$' on scope check

Any suggestions on how to investigate this further ? I think my mypy.ini file is correct because it behaves correctly with the mypy on my system(1.1.1), which is also the default version of pants2.16.0, which I am using. I am not sure how to use the mypy executable used by pants though.

[thejcannon]

This is a classic problem with tools vs. tool runners. It boils down to the behavior of the tool when configured to exclude something, yet it is explicitly provided on the command-line. You see this also with IDEs.

Note that mypy's config for exclude says:

A regular expression that matches file names, directory names and paths which mypy should ignore while recursively discovering files to check.

Here' mypy isn't discovering any files since we pass it on the command-line.

So the only way to have this work is to tell Pants to not pass the file to mypy: https://www.pantsbuild.org/v2.15/docs/reference-python_source#codeskip_mypycode