Add --readonly-app-data option

[asottile]

Resolves #2000

Thanks for contributing, make sure you address all the checklists (for details on how see

development documentation)!

• 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 #2009 (e4b182d) into main (271dd73) will increase coverage by 0.04%.
The diff coverage is 93.61%.

@@            Coverage Diff             @@
##             main    #2009      +/-   ##
==========================================
+ Coverage   94.32%   94.36%   +0.04%     
==========================================
  Files          86       87       +1     
  Lines        4280     4316      +36     
==========================================
+ Hits         4037     4073      +36     
  Misses        243      243              

Flag	Coverage Δ
tests	94.36% <93.61%> (+0.04%)	⬆️

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

Impacted Files	Coverage Δ
src/virtualenv/app_data/via_disk_folder.py	82.88% <80.00%> (-0.76%)	⬇️
src/virtualenv/app_data/read_only.py	84.21% <84.21%> (ø)
src/virtualenv/app_data/__init__.py	93.93% <92.00%> (-1.41%)	⬇️
src/virtualenv/app_data/base.py	94.11% <100.00%> (+0.24%)	⬆️
src/virtualenv/app_data/na.py	83.33% <100.00%> (+2.25%)	⬆️
src/virtualenv/app_data/via_tempdir.py	100.00% <100.00%> (+5.55%)	⬆️
src/virtualenv/run/__init__.py	95.77% <100.00%> (ø)
...virtualenv/seed/embed/via_app_data/via_app_data.py	82.17% <100.00%> (-0.18%)	⬇️
src/virtualenv/seed/wheels/bundle.py	100.00% <100.00%> (ø)
src/virtualenv/util/lock.py	99.13% <100.00%> (+0.29%)	⬆️
... and 3 more

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[asottile]

I believe this is ready for review now 🎉

[gaborbernat]

The test suite on Windows 2.7 seems to be failing. The delta coverage is 90%, can you please bring it up to 100%? Otherwise conceptually the PR looks good.

[asottile]

here's the diff cover:

• src/virtualenv/app_data/__init__.py (84.0%): Missing lines 22,28,41-42
  • (previously uncovered, just moved) https://github.com/pypa/virtualenv/pull/2009/files#diff-e2c6ee2a445e2be45e7e528ab167451b93164211148cc9a3ce05a57e8e79ddd8R22
  • (unreachable / defensive): https://github.com/pypa/virtualenv/pull/2009/files#diff-e2c6ee2a445e2be45e7e528ab167451b93164211148cc9a3ce05a57e8e79ddd8R28
  • (previously uncovered, just moved) https://github.com/pypa/virtualenv/pull/2009/files#diff-e2c6ee2a445e2be45e7e528ab167451b93164211148cc9a3ce05a57e8e79ddd8R41-R42
• src/virtualenv/app_data/base.py (100%)
• src/virtualenv/app_data/na.py (100%)
• src/virtualenv/app_data/read_only.py (84.2%): Missing lines 13,17,31
  • (trivial error case): https://github.com/pypa/virtualenv/pull/2009/files#diff-e2c6ee2a445e2be45e7e528ab167451b93164211148cc9a3ce05a57e8e79ddd8R41-R42
  • (trivial error case): https://github.com/pypa/virtualenv/pull/2009/files#diff-e2c6ee2a445e2be45e7e528ab167451b93164211148cc9a3ce05a57e8e79ddd8R41-R42
  • (trivial error case): https://github.com/pypa/virtualenv/pull/2009/files#diff-e2c6ee2a445e2be45e7e528ab167451b93164211148cc9a3ce05a57e8e79ddd8R41-R42
• src/virtualenv/app_data/via_disk_folder.py (80.0%): Missing lines 56
  • (__repr__ implementation to make debugging easier): https://github.com/pypa/virtualenv/pull/2009/files#diff-e2c6ee2a445e2be45e7e528ab167451b93164211148cc9a3ce05a57e8e79ddd8R41-R42
• src/virtualenv/app_data/via_tempdir.py (100%)
• src/virtualenv/run/__init__.py (100%)
• src/virtualenv/seed/embed/via_app_data/via_app_data.py (100%)
• src/virtualenv/seed/wheels/bundle.py (100%)
• src/virtualenv/util/lock.py (100%)

[gaborbernat]