fix(update): preserve executable bit for new files

[gcomneno]

Fixes #2630.

When a template update introduces a new executable file in a destination repository with core.fileMode=false, Git ignores the on-disk executable bit. As a result, the user's later git add records the new file as 100644 instead of 100755.

This change handles new executable files in the same executable-bit sync path used for existing files:

• if the destination has core.fileMode=false;
• and the rendered file is executable;
• and the file is not tracked yet;

Copier first creates an empty intent-to-add index entry, then updates only that entry's mode via git update-index --cacheinfo. This prepares the executable bit without staging the rendered file contents.

Added regression coverage for a template update that introduces a new executable file, verifying that:

• the file is executable on disk after update;
• the intermediate index entry has mode 100755;
• the rendered file contents are not staged;
• a later user git add records the file as 100755.

Also added coverage for new non-executable files with core.fileMode=false, ensuring Copier leaves them untracked and does not create an unnecessary intent-to-add index entry.

Tests run:

• pytest -q tests/test_updatediff.py -k "new_files_with_filemode_false or new_non_executable_files" -rs
• LC_ALL=C pytest -q tests/test_updatediff.py -k "executable_bit or exec_bit or new_non_executable_files" -rs
• LC_ALL=C pytest -q tests/test_updatediff.py -rs
• LC_ALL=C pytest -q tests/test_updatediff.py tests/test_copy.py -rs
• ruff format --check copier/_main.py tests/test_updatediff.py
• ruff check copier/_main.py tests/test_updatediff.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.24%. Comparing base (6a0db30) to head (1ff0ae8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2683      +/-   ##
==========================================
+ Coverage   97.19%   97.24%   +0.05%     
==========================================
  Files          60       60              
  Lines        7237     7299      +62     
==========================================
+ Hits         7034     7098      +64     
+ Misses        203      201       -2     

Flag	Coverage Δ
unittests	97.24% <100.00%> (+0.05%)	⬆️

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[sisp]

Isn't this the same as #2640? 🤔 (I haven't made up my mind about the best path forward yet because #2376 will resolve the same problem more fundamentally.)

[gcomneno]

Thanks for pointing that out, @sisp.

Yes, after looking at #2640, this is essentially the same direction: create an intent-to-add entry for new executable files with core.fileMode=false, then preserve the executable bit through the later user git add.

I started from #2630 and missed the existing PR, sorry for the duplicate work. #2640 is older and more complete, so I’m happy to close this PR to avoid adding noise.

If useful, feel free to reuse anything from the additional non-executable-file regression test here, but otherwise I’ll consider this superseded by #2640 / the larger #2376 direction.

[willemkokke]

Haha, just checking in on my PR (#2640) and I got really confused for a minute ;) Great minds think alike and all that!

#2376 is definitely the better solution

[gcomneno]

Thanks for checking and confirming! Since #2376 is the better solution, I'm closing this PR to avoid duplicate work.