fix: keep absolute path when os.path.relpath raises ValueError on Windows cross-drive - #3739
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… on Windows On Windows, os.path.relpath raises ValueError when the path and the current working directory are on different drives (e.g. config on C:\ but the git repository root is on D:\). _adjust_args_and_chdir called os.path.relpath unconditionally after chdir-ing to the git root, so running pre-commit with --config pointing to a different drive crashed with a ValueError instead of falling back gracefully. Add a _relpath() helper that catches ValueError and returns the original (absolute) path. Replace all four os.path.relpath() call-sites in _adjust_args_and_chdir with _relpath() so that cross-drive paths are kept as absolute paths rather than raising an unhandled exception. Fixes pre-commit#2530 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Fixes #2530.
Problem
On Windows,
os.path.relpathraisesValueErrorwhen the start pathand the target path are on different drives — for example when
--configpoints toC:\configs\pre-commit-config.yamlbut the gitrepository root is on
D:\._adjust_args_and_chdircallsos.path.relpathunconditionally afteros.chdir(toplevel), so the combination of a cross-drive config (or--commit-msg-filename/try-reporepo path) and a git repo on adifferent drive crashed with an unhandled
ValueErrorinstead offalling back gracefully.
Fix
Add a
_relpath()helper that wrapsos.path.relpathand catchesValueError, returning the original path unchanged (keeping itabsolute). All four
os.path.relpathcall-sites in_adjust_args_and_chdirare replaced with_relpath().On same-drive paths the behaviour is identical to before. On
cross-drive paths the absolute path is preserved, which is valid since
absolute paths work regardless of the current directory.
Tests
test_relpath_falls_back_on_cross_drive_valueerror— unit test thatdirectly verifies
_relpathreturns the original path whenos.path.relpathraisesValueError.test_relpath_returns_relative_path_on_same_drive— verifies thenormal (non-Windows-cross-drive) code path still works.
All existing
main_test.pytests continue to pass (30 passed, 1skipped on non-Windows).