pathlib.Path.absolute() mishandles drive-relative Windows paths

[barneygale]

Windows has one current directory per drive, and supports drive-relative paths like 'X:' and 'X:foo.txt'. This makes a conversion from relative to absolute paths more complicated than simply prepending a (single) current directory.

It's correctly handled in ntpath.abspath() by calling NT's GetFullPathNameW() function. But in pathlib we simply prepend os.getcwd(), leading to incorrect results:

>>> import os, nt, pathlib
>>> os.chdir('Z:/build')
>>> os.chdir('C:/')
>>> os.path.abspath('Z:')
'Z:\\build'
>>> nt._getfullpathname('Z:')
'Z:\\build'
>>> pathlib.Path('Z:').absolute()
WindowsPath('Z:')

This bug is present in all versions of CPython pathlib. We can't fix it by calling abspath() because it will also normalize the path, eliding '..' parts.

Linked PRs

• gh-100809: Fix handling of drive-relative paths in pathlib.Path.absolute() #100812
• [3.11] gh-100809: Fix handling of drive-relative paths in pathlib.Path.absolute() (GH-100812) #101993

[barneygale]

Fixed in #100812 (3.12), not backported due to interactions with other recent pathlib work.