Checking modules with the same name in different folders fails.

[jenstroeger]

The following is a simplification of pytest’s conftest.py scenario, but can be reproduced fairly simply — it boils down to checking files (modules) with the same name in different folders with a single mypy invocation:

(.venv) > mkdir test
(.venv) > mkdir test/foo
(.venv) > mkdir test/bar
(.venv) > touch test/foo/same.py
(.venv) > touch test/bar/same.py
(.venv) > mypy test/foo/same.py 
Success: no issues found in 1 source file
(.venv) > mypy test/bar/same.py 
Success: no issues found in 1 source file

However, checking both files together causes the following error:

(.venv) > mypy test/foo/same.py test/bar/same.py 
test/bar/same.py: error: Duplicate module named "same" (also at "test/foo/same.py")
test/bar/same.py: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#mapping-file-paths-to-modules for more info
test/bar/same.py: note: Common resolutions include: a) using `--exclude` to avoid checking one of them, b) adding `__init__.py` somewhere, c) using `--explicit-package-bases` or adjusting MYPYPATH
Found 1 error in 1 file (errors prevented further checking)
(.venv) > mypy test/
test/foo/same.py: error: Duplicate module named "same" (also at "test/bar/same.py")
test/foo/same.py: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#mapping-file-paths-to-modules for more info
test/foo/same.py: note: Common resolutions include: a) using `--exclude` to avoid checking one of them, b) adding `__init__.py` somewhere, c) using `--explicit-package-bases` or adjusting MYPYPATH
Found 1 error in 1 file (errors prevented further checking)

I don’t really want to add __init__.py files to turn these folders into (sub)packages, because they’re simply independent files.

To Reproduce

See above.

Expected Behavior

That mypy checks both files and succeeds.

Actual Behavior

Above error.

Your Environment

• Mypy version used: mypy 1.6.1 (compiled: yes)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: Python 3.11.6 (main, Oct 2 2023, 17:45:58) [Clang 14.0.3 (clang-1403.0.22.14.1)] on darwin

[ilevkivskyi]

Have you tried --explicit-package-bases as the error message says? Anyway, it is a duplicate of #10428 (even though I don't understand what that issue is about, most use cases should be covered by this flag).