[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

[johnwparent]

Please remove this object file in general, but also from the history of this PR

[johnwparent]

This is very close. I think the change we want to make though is to extract the long path prefix, and then make choices based on what follows it.

There are a few cases where we do want to return a path with the longpath prefix (because failing to do so would produce a broken path) like \\?\Volume{GUID}, we only want to strip the longpath if it precedes a path like a networked path or local absolute drive prefixed path.

UNC paths are also case insensitive.

Suggested change

	if path.startswith("\\\\?\\UNC\\"):
	return "\\\\" + path[len("\\\\?\\UNC\\") :]
	if path.startswith("\\\\?\\"):
	return path[len("\\\\?\\") :]
	return path
	prefix = "\\\\?\\"
	if not path.startswith(prefix):
	return path
	rest = path[len(prefix) :]
	if rest[:4].upper() == "UNC\\":
	return "\\\\" + rest[4:]
	if ntpath.splitdrive(rest)[0]:
	return rest
	return path

Note: this suggestion requires an ntpath import.

[johnwparent]

Let's add:

• drive relative paths,
• standard relative paths,
• \?\Volume{}\spack (GUID can be more or less whatever you want)

Let's also make this test Windows only pytest.mark.only_windows(...