Resolver error message is misleading when requested extra is only available in incompatible versions

[ThiefMaster]

pip version

21.0.1

Python version

3.9.2

OS

Linux

Additional information

No response

Description

If I try to install a package with the requirements Authlib==1.0.0a1, Flask-Multipass>=0.3.1,<0.4-dev, Flask-Multipass-CERN pip is not able to install it because of Flask-Multipass-CERN requiring Flask-Multipass[authlib] which in turn
requires authlib[client]>=0.14.1,<1.0.

However, since Version('1.0.0a1') < Version('1.0') succeeds (with the Version class from packaging), I would expect the dependency resolution to succeed.

Expected behavior

The specified packages should be installed.

How to Reproduce

Create a setup.cfg containing this:

[metadata]
name = deptest
version = 1.0-dev

[options]
install_requires =
    Authlib==1.0.0a1
    Flask-Multipass>=0.3.1,<0.4-dev
    Flask-Multipass-CERN

and a setup.py with

from setuptools import setup
setup()

Run pip install -e .

Output

[adrian@claptrap:/tmp/deptest]> pip install -e .
Obtaining file:///tmp/deptest
Collecting Authlib==1.0.0a1
  Using cached Authlib-1.0.0a1-py2.py3-none-any.whl (207 kB)
Collecting Flask-Multipass<0.4-dev,>=0.3.1
  Using cached Flask_Multipass-0.3.3-py2.py3-none-any.whl (38 kB)
Collecting Flask-Multipass-CERN
  Using cached Flask_Multipass_CERN-1.0.dev4-py2.py3-none-any.whl (6.1 kB)
Collecting cryptography<4,>=3.2
  Using cached cryptography-3.4.6-cp36-abi3-manylinux2014_x86_64.whl (3.2 MB)
Collecting cffi>=1.12
  Using cached cffi-1.14.5-cp39-cp39-manylinux1_x86_64.whl (406 kB)
Collecting pycparser
  Using cached pycparser-2.20-py2.py3-none-any.whl (112 kB)
Collecting Flask>=0.10.1
  Using cached Flask-1.1.2-py2.py3-none-any.whl (94 kB)
Collecting blinker
  Using cached blinker-1.4.tar.gz (111 kB)
Collecting Jinja2>=2.10.1
  Using cached Jinja2-2.11.3-py2.py3-none-any.whl (125 kB)
Collecting click>=5.1
  Using cached click-7.1.2-py2.py3-none-any.whl (82 kB)
Collecting itsdangerous>=0.24
  Using cached itsdangerous-1.1.0-py2.py3-none-any.whl (16 kB)
Collecting Werkzeug>=0.15
  Using cached Werkzeug-1.0.1-py2.py3-none-any.whl (298 kB)
Collecting MarkupSafe>=0.23
  Using cached MarkupSafe-1.1.1-cp39-cp39-manylinux2010_x86_64.whl (32 kB)
Collecting authlib[client]<1.0,>=0.14.1
  Using cached Authlib-0.15.3-py2.py3-none-any.whl (203 kB)
  Using cached Authlib-0.15.2-py2.py3-none-any.whl (203 kB)
  Using cached Authlib-0.15.1-py2.py3-none-any.whl (203 kB)
  Using cached Authlib-0.15-py2.py3-none-any.whl (202 kB)
  Using cached Authlib-0.14.3-py2.py3-none-any.whl (215 kB)
  Using cached Authlib-0.14.2-py2.py3-none-any.whl (227 kB)
  Using cached Authlib-0.14.1-py2.py3-none-any.whl (227 kB)
INFO: pip is looking at multiple versions of flask-multipass[authlib] to determine which version is compatible with other requirements. This could take a while.
Collecting flask-multipass[authlib]>=0.3.dev5
  Using cached Flask_Multipass-0.3.2-py2.py3-none-any.whl (38 kB)
  Using cached Flask_Multipass-0.3.1-py2.py3-none-any.whl (38 kB)
  Using cached Flask_Multipass-0.3-py2.py3-none-any.whl (38 kB)
  Using cached Flask_Multipass-0.3.dev5-py2.py3-none-any.whl (38 kB)
INFO: pip is looking at multiple versions of flask-multipass to determine which version is compatible with other requirements. This could take a while.
INFO: pip is looking at multiple versions of flask-multipass-cern to determine which version is compatible with other requirements. This could take a while.
Collecting Flask-Multipass-CERN
  Using cached Flask_Multipass_CERN-1.0.dev3-py2.py3-none-any.whl (6.0 kB)
  Using cached Flask_Multipass_CERN-1.0.dev2-py2.py3-none-any.whl (5.8 kB)
  Using cached Flask_Multipass_CERN-1.0.dev1-py2.py3-none-any.whl (5.7 kB)
  Using cached Flask_Multipass_CERN-1.0.dev0-py2.py3-none-any.whl (5.8 kB)
INFO: pip is looking at multiple versions of flask-multipass[authlib] to determine which version is compatible with other requirements. This could take a while.
INFO: pip is looking at multiple versions of flask-multipass to determine which version is compatible with other requirements. This could take a while.
INFO: This is taking longer than usual. You might need to provide the dependency resolver with stricter constraints to reduce runtime. If you want to abort this run, you can press Ctrl + C to do so. To improve how pip performs, tell us what happened here: https://pip.pypa.io/surveys/backtracking
INFO: pip is looking at multiple versions of blinker to determine which version is compatible with other requirements. This could take a while.
Collecting blinker
  Using cached blinker-1.3.tar.gz (91 kB)
  Using cached blinker-1.2.tar.gz (66 kB)
  Using cached blinker-1.1.zip (79 kB)
  Using cached blinker-1.0.tar.gz (61 kB)
  Using cached blinker-0.9.tar.gz (60 kB)
  Using cached blinker-0.8.tar.gz (9.8 kB)
INFO: This is taking longer than usual. You might need to provide the dependency resolver with stricter constraints to reduce runtime. If you want to abort this run, you can press Ctrl + C to do so. To improve how pip performs, tell us what happened here: https://pip.pypa.io/surveys/backtracking
INFO: pip is looking at multiple versions of flask-multipass-cern to determine which version is compatible with other requirements. This could take a while.
INFO: This is taking longer than usual. You might need to provide the dependency resolver with stricter constraints to reduce runtime. If you want to abort this run, you can press Ctrl + C to do so. To improve how pip performs, tell us what happened here: https://pip.pypa.io/surveys/backtracking
^CERROR: Operation cancelled by user

Code of Conduct

• I agree to follow the PSF Code of Conduct

[uranusjr]

Can you try if installation would work if you add an additional requirement authlib[client]==1.0.0a1? I think I may know what’s going on.

[ThiefMaster]

While trying to do that I just realized that authlib==1.0.0a no longer has a [client] extra (lepture/authlib#327)... I guess that explains it...

[uranusjr]

Oof, that's unfortunate. I wonder how we can make the error message clearer. What would you expect the log to show in this situation?

[ThiefMaster]

With Authlib==1.0.0a1 being an exact requirement, where trying other authlib versions makes no sense, I think an error clearly indicating that there is no [client] extra (or whatever other reason prevents it from being installed) would help a lot.

[uranusjr]

Thanks, I’ll use this to track this enhancement.