KeyError fired from importlib during collection when running with --import-mode=importlib on a directory containing a same-named one

[redsun82]

A detailed description of the bug or problem you are having

When creating the following structure:

x/
├─ y/
│  ├─ y/
│  ├─ test_y.py

then pytest --import-mode=importlib fails with the following cryptic message:

================================= ERRORS =================================
_____________________ ERROR collecting x/y/test_y.py _____________________
<frozen importlib._bootstrap_external>:1448: in find_spec
    ???
<frozen importlib._bootstrap_external>:1222: in __init__
    ???
<frozen importlib._bootstrap_external>:1238: in _get_parent_path
    ???
E   KeyError: 'x'

To trigger this bug:

• the directory containing the test needs to be within at least another directory, it can't be directly underneath the root path
• the directory containing the test must in turn contain another directory with the same base name

Running with --pdb gives a slightly more useful backtrace:

  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/runner.py(341)from_call()
-> result: Optional[TResult] = func()
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/runner.py(389)collect()
-> return list(collector.collect())
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/python.py(548)collect()
-> self._register_setup_module_fixture()
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/python.py(561)_register_setup_module_fixture()
-> self.obj, ("setUpModule", "setup_module")
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/python.py(287)obj()
-> self._obj = obj = self._getobj()
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/python.py(545)_getobj()
-> return importtestmodule(self.path, self.config)
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/python.py(492)importtestmodule()
-> mod = import_path(
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/pathlib.py(565)import_path()
-> mod = _import_module_using_spec(
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/pathlib.py(660)_import_module_using_spec()
-> parent_module = _import_module_using_spec(
  /home/redsun82/.cache/pypoetry/virtualenvs/foo-4uHc0o_q-py3.10/lib/python3.10/site-packages/_pytest/pathlib.py(633)_import_module_using_spec()
-> spec = meta_importer.find_spec(module_name, [str(module_location)])
  <frozen importlib._bootstrap_external>(1448)find_spec()
  <frozen importlib._bootstrap_external>(1222)__init__()
> <frozen importlib._bootstrap_external>(1238)_get_parent_path()

Output of pip list from the virtual environment you are using

I tried this on a minimal poetry env with just pytest

-------------- -------
exceptiongroup 1.2.1
iniconfig      2.0.0
packaging      24.1
pip            24.0
pluggy         1.5.0
pytest         8.2.2
setuptools     70.0.0
tomli          2.0.1

pytest and operating system versions

pytest 8.2.2. Encountered this both with python 3.10 and python 3.12, so the python version doesn't seem to be a factor.

Running on Ubuntu 22.04.4 LTS.

cc @criemen who encountered this

[Zac-HD]

Feels like this might be an upstream issue; we should try to get a reproducer using stdlib code only.