Using a drive letter in a URI breaks (Windows)

[henryiii]

Description

If you use a URI on Windows for PIP_CONSTRAINTS, then pip breaks down with an error like this:

ERROR: Could not open requirements file: [Errno 22] Invalid argument: '/C:/Users/VssAdministrator/AppData/Local/Temp/pytest-of-VssAdministrator/pytest-1/test_dependency_constraints_fi1/constraints file.txt'

This was supposed to be a workaround for #10114. Seen in pypa/cibuildwheel#738 (comment)

Expected behavior

URIs from path lib should work on Windows.

pip version

21.1.3

Python version

All

OS

Windows and macOS, at least, probably all.

How to Reproduce

1. Get a URI, say from pathlib's Path.as_uri().
2. Set PIP_CONSTRAINTS with it and install something
3. An error occurs.

Output

ERROR: Could not open requirements file: [Errno 22] Invalid argument: '/C:/Users/VssAdministrator/AppData/Local/Temp/pytest-of-VssAdministrator/pytest-1/test_dependency_constraints_fi1/constraints file.txt'

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

Turns out this is a limitation to urllib.parse.urlsplit() (which pip uses to parse file:// URLs).

>>> from pathlib import Path
>>> from urllib.parse import urlsplit
>>> scheme, netloc, path, *_ = urlsplit(Path("C:/Users/VssAdministrator").as_posix())
# scheme == "file"
# netloc == ""
# path == "/C:/Users/VssAdministrator"

This leading slash unfortunately causes issues in functions like open(). Windows can take a UNC path, /Users/VssAdministrator (without the drive name, as long as you are on the same drive), or C:/Users/VssAdministrator (the one we all know), but not /C:/Users/VssAdministrator.

I’ll submit a hack to work around this.