Fix activator path in cygwin and msys2

[danyeaw]

Closes #1940. In cygwin and MSYS2, the path is in POSIX format. This PR converts the Windows path to POSIX format using the cygpath utility so that it is added to the bash activation script in the correct format.

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• ran the linter to address style issues (tox -e fix_lint)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation

[codecov]

Codecov Report

Merging #1946 into master will decrease coverage by 8.34%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master    #1946      +/-   ##
==========================================
- Coverage   93.92%   85.57%   -8.35%     
==========================================
  Files          86       86              
  Lines        4228     4237       +9     
==========================================
- Hits         3971     3626     -345     
- Misses        257      611     +354     

Flag	Coverage Δ
#tests	85.57% <77.77%> (-8.35%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/virtualenv/activation/via_template.py	96.15% <77.77%> (-3.85%)	⬇️
src/virtualenv/discovery/windows/pep514.py	0.00% <0.00%> (-100.00%)	⬇️
src/virtualenv/discovery/windows/__init__.py	0.00% <0.00%> (-100.00%)	⬇️
src/virtualenv/util/subprocess/_win_subprocess.py	0.00% <0.00%> (-95.09%)	⬇️
src/virtualenv/util/path/_pathlib/via_os_path.py	0.00% <0.00%> (-91.51%)	⬇️
src/virtualenv/create/via_global_ref/store.py	50.00% <0.00%> (-40.00%)	⬇️
src/virtualenv/activation/batch/__init__.py	66.66% <0.00%> (-33.34%)	⬇️
.../create/via_global_ref/builtin/cpython/cpython3.py	67.39% <0.00%> (-28.27%)	⬇️
src/virtualenv/info.py	77.50% <0.00%> (-22.50%)	⬇️
...nv/create/via_global_ref/builtin/cpython/common.py	86.84% <0.00%> (-13.16%)	⬇️
... and 12 more

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[danyeaw]

@gaborbernat I have updated the PR with the regex 👍
I noticed on the tests side that the activator isn't run in Windows because of WSL on GitHub Actions. Any thoughts on if additional tests could be added somehow?

[gaborbernat]

Any thoughts on if additional tests could be added somehow?

Write a uni test. Mock sysconfig.get_platform, check generated scripts contain correct path.

[danyeaw]

@gaborbernat Thanks for the feedback, I have been exploring how to structure mock tests since I don't have much experience mocking things out. I'm hoping to finish it this weekend. Can we reopen this PR?

[gaborbernat]

@danyeaw I did not close this PR on purpose. Was a side-effect of renaming the default branch to main. Please reopen the PR against the main branch. Sorry.

[danyeaw]

@gaborbernat No problem, I like the main branch rename! I have submitted #1952.