`os-path-expanduser` (PTH111) should be marked unsafe

[dscorbett]

Summary

The fix for os-path-expanduser (PTH111) should be marked unsafe because the replacement is not always equivalent. If os.path.expanduser can’t determine a home directory, it returns the input unchanged, whereas pathlib.Path.expanduser raises an error. One reason it might not be able to determine a home directory is if the indicated user does not exist, but that is not the only possible reason. Example:

$ cat >pth111.py <<'# EOF'
import os
try: print(os.path.expanduser("~pth111_nonexistent_user"))
except RuntimeError as e: print(e)
# EOF

$ python pth111.py
~pth111_nonexistent_user

$ ruff --isolated check pth111.py --select PTH111 --preview --fix
Found 1 error (1 fixed, 0 remaining).

$ cat pth111.py
import os
import pathlib
try: print(pathlib.Path("~pth111_nonexistent_user").expanduser())
except RuntimeError as e: print(e)

$ python pth111.py
Could not determine home directory.

Version

ruff 0.12.11 (c2bc15b 2025-08-28)