Error when %TEMP% is a junction to a dir on a letter-less drive

[grv87]

Description

Error when %TEMP% is a junction to a dir on a letter-less drive.

The error looks similar to jazzband/pip-tools#1061, but in pip itself.

Expected behavior

Successful install/reinstall

pip version

21.3

Python version

3.10.0, 3.9.6, 3.8.2

OS

Windows 10 x64

How to Reproduce

1. Create a volume and don't assign a letter to it
2. Create dir on this volume
3. Create a junction on this dir:
   ln--junction junction ‪\\?\Volume{<new volume uuid>}\dir
4. set TEMP=%cd%\junction
5. Install some package: pip3 install CrossMap

Output

Traceback (most recent call last):
  File "<python_install_dir>\lib\site-packages\pip\_internal\cli\base_command.py", line 164, in exc_logging_wrapper
    status = run_func(*args)
  File "<python_install_dir>\lib\site-packages\pip\_internal\cli\req_command.py", line 204, in wrapper
    return func(self, options, args)
  File "<python_install_dir>\lib\site-packages\pip\_internal\commands\install.py", line 294, in run
    wheel_cache = WheelCache(options.cache_dir, options.format_control)
  File "<python_install_dir>\lib\site-packages\pip\_internal\cache.py", line 219, in __init__
    self._ephem_cache = EphemWheelCache(format_control)
  File "<python_install_dir>\lib\site-packages\pip\_internal\cache.py", line 196, in __init__
    super().__init__(self._temp_dir.path, format_control)
  File "<python_install_dir>\lib\site-packages\pip\_internal\cache.py", line 121, in __init__
    super().__init__(cache_dir, format_control, {"binary"})
  File "<python_install_dir>\lib\site-packages\pip\_internal\cache.py", line 44, in __init__
    assert not cache_dir or os.path.isabs(cache_dir)
AssertionError

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

What would the value of cache_dir be in this case? I wonder if this is can be simply fixed by switching to pathlib (which handles UNC paths better than os.path). Also, I wonder if the directory junction is actually relevant here; what happens if TEMP is set directly to the network drive?

[grv87]

cache_dir: Volume{<new volume uuid>}\dir\pip-ephem-wheel-cache-...

Note that \\?\ prefix is lost.

TEMP set to network UNC path works.
But my TEMP dir is not on a network drive. Junctions can't target network drives.

[pfmoore]

Following the chain of calls leads to os.path.realpath(tempfile.mkdtemp(prefix=f"pip-{kind}-")). Can you confirm what that call returns in your environment? (Clearly you can just use any old prefix for the call).

If it doesn't return a valid path, that would imply a Python bug (which we might be able to work around, but I'd also like to make sure the root issue is reported if that's what it is).

[grv87]

os.path.realpath returns Volume{uuid}\\dir\\pip-kind-.... Yes, the prefix is lost.

I've reported https://bugs.python.org/issue45597.

[uranusjr]

Does pathlib.Path.resolve() have the same issue? If not, we can just use that instead.

[grv87]

@uranusjr, yes, it has the same issue too.

If I'm the single user affected then I'm ready to wait for the fix in Python. I don't use pip very often, and there is the obvious workaround (set TEMP to local dir before a run). Feel free to close this issue.