pip 20.2b1/Py2.7: Cannot install pylint (environment marker conflicts)

[jamadden]

Working with the pip 20.2b1 unstable resolver in an existing virtual environment, I am unable to install gevent's dev-requirements.txt on Python 2.7 with the alpha resolver. Normal resolver works fine. The error happens with and without the -U option to pip.

$  pip --unstable-feature=resolver install  -r dev-requirements.txt
Requirement already satisfied: restview in //lib/python2.7/site-packages (from -r dev-requirements.txt (line 4)) (2.9.2)
Requirement already satisfied: pylint>=1.8.0 in //lib/python2.7/site-packages (from -r dev-requirements.txt (line 6)) (1.9.4)
ERROR: Could not find a version that satisfies the requirement pylint>=1.8.0
ERROR: Could not find a version that satisfies the requirement pylint>=2.5.0
ERROR: No matching distribution found for pylint, pylint

The relevant lines of dev-requirements.txt look like this:

restview

pylint>=1.8.0 ; python_version < "3.4"
# pylint 2 needs astroid 2; unfortunately, it uses `typed_ast`
# which has a C extension that doesn't build on PyPy
pylint >= 2.5.0 ; python_version >= "3.4"  and platform_python_implementation == "CPython"
astroid >= 2.4.0 ; python_version >= "3.4" and platform_python_implementation == "CPython"

I can provide the pipdeptree if desired, but it's quite large as this is an old virtual environment.

cc @ei8fdb @nlhkabu

[pradyunsg]

This is basically the same as #8363 as far as I can tell. Similar reasoning appiles -- could you try this against master?

[jamadden]

Fixed in master. Thanks!