Result of os.path.realpath("") is incorrect if cwd is on letter-less drive (\\?\-prefixed)

Bug report

1. Create volume, dir on it, don't assign a drive letter
2. In Python:

>>> import os
>>> os.chdir("\\\\?\\Volume{<uuid>}\\<dir>")
>>> os.path.realpath("")
'\\\\?\\Volume{<uuid>}\\<dir>\\.'

The dot is invalid in \\?\-prefixed path.
Dots (. and ..) are normalized by Windows API (at least on NTFS). But \\?\ paths bypass normalization and so may not contain dots. See, for example, here.
All later WinAPI calls with this path fail.

As a simple test, dir \\?\Volume{<uuid>}\dir\. doesn't work whereas dir \\?\Volume{<uuid>}\dir works.

P.S. os.path.realpath(".") gives the same invalid result

Your environment

CPython 3.10.0
Windows 10

Context
The problem arises from pip.
sys.path contains empty string (meaning current dir I presume).
And legacy installation method resolves sys.path relatively to cwd.

Investigation
Here:
https://github.com/python/cpython/blob/4bed0db7c222f8df1b4e31107c0305214caf3f56/Lib/ntpath.py#L704
os.path.join still adds slash even if the second argument is empty. And if the path is ended with slash, dot is added somewhere below.

I fixed it to:

path = cwd if path == "." or path == "" else join(cwd, path)

Commencez dans Lib/ntpath.py autour de la ligne référencée 704 et reproduisez le comportement de Windows avec un chemin de volume \?-préfixé dont le répertoire courant n’a pas de lettre de lecteur. Vérifiez comment os.path.realpath("") et os.path.realpath(".") construisent leurs chemins, puis ajoutez une couverture de régression montrant qu’aucun des deux résultats ne se termine par un composant \. invalide et que le chemin obtenu fonctionne avec les appels WinAPI ultérieurs.