Invalid requirement error with file URL and named project

[jaraco]

Description

It's possible to install using a git+file scheme:

$ pip install 'git+file:///Users/jaraco/m/pytest-perf'
...
Installed...

It's also possible to specify the distribution name and extras when installing from a remote git repo:

$ pip install 'pytest-perf@git+https://github.com/jaraco/m/pytest-perf'
...
Installed...

But if one tries to install using a git+file scheme and specify the distribution name, an Invalid requirement error occurs:

$ pip install 'pytest-perf@git+file:///Users/jaraco/m/pytest-perf'
ERROR: Invalid requirement: 'pytest-perf@git+file:///Users/jaraco/m/pytest-perf'
Hint: It looks like a path. File 'pytest-perf@git+file:///Users/jaraco/m/pytest-perf' does not exist.

And thus because of #10097, it's not possible to install a local git repo with extras.

I'd really like for there to be some way to install a package at a given revision with extras:

$ pip install '*[testing]@git+file:path/to/repo@rev'

I need this for pytest-perf in order to compare performance of a package against the main branch.

Expected behavior

Honor the combination of the two syntaxes.

pip version

21.1.2

Python version

3.9.2

OS

macOS 11.4

How to Reproduce

x

Output

No response

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[uranusjr]

Looks like a deficiency in packaging:

>>> packaging.requirements import Requirement
>>> Requirement('pytest-perf@git+file:///Users/jaraco/m/pytest-perf')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "packaging/requirements.py", line 130, in __init__
    raise InvalidRequirement("Invalid URL: {0}".format(req.url))
packaging.requirements.InvalidRequirement: Invalid URL: git+file:///Users/jaraco/m/pytest-perf

Specifically, packaging does not seem to allow non-file: URLs without a netloc. But pip’s VCS URLs aren’t file: (but git+file: in this case) and thus rejected by packaging. Personally I feel packaging’s rules are a bit too restrictive; PEP 508 does not specify what URLs are allowed, so instead of trying to decide it for the user, it should either just return whatever is passed in (and let the user perform additional checks), or allow some customisation on the validation logic.

I will open an issue on packaging linking here.