pre-commit · M001N · Aug 10, 2026 · Aug 10, 2026
diff --git a/pre_commit/main.py b/pre_commit/main.py
@@ -172,6 +172,16 @@ def _add_run_options(parser: argparse.ArgumentParser) -> None:
     )
 
 
+def _relpath_or_abspath(path: str) -> str:
+    # on windows, `os.path.relpath` raises `ValueError` when `path` and the
+    # current working directory are on different drives / mounts -- fall
+    # back to the (already absolute) path in that case
+    try:
+        return os.path.relpath(path)
+    except ValueError:
+        return os.path.abspath(path)
+
+
 def _adjust_args_and_chdir(args: argparse.Namespace) -> None:
     # `--config` was specified relative to the non-root working directory
     if os.path.exists(args.config):
@@ -188,15 +198,15 @@ def _adjust_args_and_chdir(args: argparse.Namespace) -> None:
     toplevel = git.get_root()
     os.chdir(toplevel)
 
-    args.config = os.path.relpath(args.config)
+    args.config = _relpath_or_abspath(args.config)
     if args.command in {'run', 'try-repo'}:
-        args.files = [os.path.relpath(filename) for filename in args.files]
+        args.files = [_relpath_or_abspath(filename) for filename in args.files]
         if args.commit_msg_filename is not None:
-            args.commit_msg_filename = os.path.relpath(
+            args.commit_msg_filename = _relpath_or_abspath(
                 args.commit_msg_filename,
             )
     if args.command == 'try-repo' and os.path.exists(args.repo):
-        args.repo = os.path.relpath(args.repo)
+        args.repo = _relpath_or_abspath(args.repo)
 
 
 def main(argv: Sequence[str] | None = None) -> int:

diff --git a/tests/main_test.py b/tests/main_test.py
@@ -37,6 +37,76 @@ def test_adjust_args_and_chdir_noop(in_git_dir):
     assert args.files == ['f1', 'f2']
 
 
+def test_adjust_args_and_chdir_cross_drive_config(in_git_dir):
+    # on windows, `os.path.relpath` raises `ValueError` when the two
+    # paths are on different drives/mounts (e.g. config on `C:`, repo on
+    # `D:`) -- simulate that here so the test doesn't require an actual
+    # second drive to exist
+    in_git_dir.join(C.CONFIG_FILE).ensure()
+    args = _args(command='run', files=[])
+    abs_config = os.path.abspath(args.config)
+
+    real_relpath = os.path.relpath
+
+    def relpath(path, *args, **kwargs):
+        if path == abs_config:
+            raise ValueError("path is on mount 'C:', start on mount 'D:'")
+        return real_relpath(path, *args, **kwargs)
+
+    with mock.patch.object(os.path, 'relpath', side_effect=relpath):
+        main._adjust_args_and_chdir(args)
+
+    assert os.getcwd() == in_git_dir
+    assert args.config == abs_config
+
+
+def test_adjust_args_and_chdir_cross_drive_files(in_git_dir):
+    # `args.files` and `args.commit_msg_filename` go through the same
+    # `os.path.relpath` call and share the same cross-drive failure mode
+    # as `args.config` -- make sure they fall back to the absolute path
+    # too (e.g. `pre-commit run --files <path-on-other-drive>`)
+    f1 = in_git_dir.join('f1').ensure()
+    args = _args(
+        command='run',
+        files=[str(f1)],
+        commit_msg_filename=str(f1),
+    )
+    abs_f1 = os.path.abspath(str(f1))
+
+    real_relpath = os.path.relpath
+
+    def relpath(path, *args, **kwargs):
+        if path == abs_f1:
+            raise ValueError("path is on mount 'C:', start on mount 'D:'")
+        return real_relpath(path, *args, **kwargs)
+
+    with mock.patch.object(os.path, 'relpath', side_effect=relpath):
+        main._adjust_args_and_chdir(args)
+
+    assert args.files == [abs_f1]
+    assert args.commit_msg_filename == abs_f1
+
+
+def test_adjust_args_try_repo_cross_drive_repo(in_git_dir):
+    # `args.repo` shares the same cross-drive failure mode too (e.g.
+    # `pre-commit try-repo` with a repo on another drive)
+    with in_git_dir.join('foo').ensure_dir().as_cwd():
+        args = _args(command='try-repo', repo='../foo', files=[])
+        abs_repo = os.path.abspath(args.repo)
+
+        real_relpath = os.path.relpath
+
+        def relpath(path, *args, **kwargs):
+            if path == abs_repo:
+                raise ValueError("path is on mount 'C:', start on mount 'D:'")
+            return real_relpath(path, *args, **kwargs)
+
+        with mock.patch.object(os.path, 'relpath', side_effect=relpath):
+            main._adjust_args_and_chdir(args)
+
+        assert args.repo == abs_repo
+
+
 def test_adjust_args_and_chdir_relative_things(in_git_dir):
     in_git_dir.join('foo/cfg.yaml').ensure()
     with in_git_dir.join('foo').as_cwd():