module __file__ attribute is not the canonical path

[woutdenolf]

closes #11816

What

Undo #11708 and replace it will a more general fix of anymodule.__file__ not having the right casing.

This fails on Windows (python 3.8, pytest 8.0.0rc2):

python -m pip install "ewokscore==0.7.1" matplotlib ipykernel^
    git+https://github.com/pytest-dev/pytest.git@b0c7f923aa39f0765425c367a02f53b1d97915f6 --no-cache
python -m pytest -v --pyargs ewokscore.tests

This MR fixes it:

python -m pip install "ewokscore==0.7.1" matplotlib ipykernel^
    git+https://github.com/woutdenolf/pytest.git@module_file_resolve --no-cache
python -m pytest -v --pyargs ewokscore.tests

Test with the h5py CI that was broken by the issue: h5py/h5py#2368

Notes

• we need to use realpath, abspath is not enough: module __file__ attribute is not the canonical path #11821 (comment)
• it seems we need to preserve symlinks: Fix issue where working dir becomes wrong on subst drive on Windows. Fixes #5965 #6523
• the behavior of TestPytestPluginInteractions.test_conftestpath_case_sensitivity is expected to change (https://github.com/pytest-dev/pytest/pull/11708/files#r1447814841) but this MR changes it in a way that was not intended (config.pluginmanager.get_plugin returns None when the string case is not the real path case)

[woutdenolf]

Note that abspath would not be enough.

Python 3.8.10 (tags/v3.8.10:3d8993a, May  3 2021, 11:48:03) [MSC v.1928 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import ewokscore
>>> import os
>>> os.path.realpath(ewokscore.__file__)
'C:\\Users\\denolf\\virtualenvs\\testenv\\py3.8\\Lib\\site-packages\\ewokscore\\__init__.py'
>>> os.path.abspath(ewokscore.__file__)
'C:\\Users\\denolf\\virtualenvs\\testenv\\py3.8\\lib\\site-packages\\ewokscore\\__init__.py'

The correct path is C:\\Users\\denolf\\virtualenvs\\testenv\\py3.8\\Lib\\site-packages\\ewokscore\\__init__.py

[woutdenolf]

Approach #11825 was selected instead of this one.