[kayaal34]

sanitize_win_longpath used path.lstrip("\\\\?\\"). str.lstrip takes a set of characters, not a prefix, so it removes every leading \ and ?:

input	before	after
\\?\C:\spack\opt	C:\spack\opt	C:\spack\opt
\\server\share\spack (UNC, no prefix)	server\share\spack	\\server\share\spack
\\?\UNC\server\share\spack	UNC\server\share\spack	\\server\share\spack
?dir\file	dir\file	?dir\file

It is used by _windows_readlink, so on Windows a symlink pointing to a network share came back as a relative-looking server\share\... (or UNC\server\... when os.readlink returns the extended form). The function now checks for the prefix, and maps \\?\UNC\ back to \\, the same way CPython's ntpath does.

Added a parametrized test_sanitize_win_longpath in lib/spack/spack/test/util/path.py (pure string checks, so it runs on any platform); three of the cases fail without the change. ruff check and ruff format --check pass on both files.

Note: I found this with a static check (ruff PLE1310) and used Claude (an AI assistant) to help write the fix and test; I reviewed and ran them.

[johnwparent]

Thanks for this! Looks pretty good and catches a bone-headed bug I added.
Just a couple of small things

[kayaal34]

Thanks for the review, @johnwparent. Updated (force-pushed, still one commit):

• main.obj is gone from the commit and the history (it was a build artifact from a local test run, sorry about that).
• Took your suggestion: the prefix is stripped only when what follows is UNC\ (case-insensitive, mapped back to \\) or a drive according to ntpath.splitdrive; otherwise the path is returned unchanged, so \\?\Volume{GUID}\... keeps its prefix.
• Added cases for lower-case unc, a drive-relative path (\\?\C:spack\opt), a Volume GUID path, a prefixed path with no drive, and plain relative / drive-relative paths without the prefix. The test is now only_windows.

All 12 cases pass; against the previous revision of this PR three of them fail (lower-case unc, Volume GUID, prefix with no drive).

[johnwparent]

Looks good now, thanks!

[johnwparent]

Thanks for the interest in Spack on Windows @kayaal34! Please don't hesitate to reach out on our Spack on Windows slack channel if you have any other questions.