requirements resolving fails with pip >= 20.3 and works with <20.3

[thrix]

After moving to pip >= 20.3 we are not able to install our requirements which installs just find with pip < 20.3

To reproduce:

$ virtualenv venv

$ source venv/bin/activate

(vent) $ cat > requirements.txt <<EOF
ansi2html==1.5.2
ansible-vault==1.2.0
black==19.10b0
flake8==3.7.9
gluetool
hypothesis==5.5.4
Jinja2==2.11.1
mypy==0.740
mypy-extensions==0.4.1
pre-commit==2.6.0
pytest==6.0.1
pytest-forked==1.1.3
pytest-html==2.0.1
pytest-localserver==0.4.1
pytest-metadata==1.8.0
pytest-mock==2.0.0
pytest-xdist==2.0.0
ruamel.yaml==0.15.51
ruamel.yaml.clib==0.2.0
tft-artemis
stackprinter==0.2.3
yamllint==1.20.0
EOF

(venv) $ python3 --version
Python 3.7.7

(venv) $ pip --version
pip 20.3.1 from /home/batman/venvs/pip/lib/python3.7/site-packages/pip (python 3.7)

(venv) $ pip install -r requirements.txt
Collecting ansi2html==1.5.2
  Using cached ansi2html-1.5.2-py3-none-any.whl
Collecting ansible-vault==1.2.0
  Using cached ansible_vault-1.2.0-py3-none-any.whl
Collecting black==19.10b0
  Using cached black-19.10b0-py36-none-any.whl (97 kB)
Collecting flake8==3.7.9
  Using cached flake8-3.7.9-py2.py3-none-any.whl (69 kB)
Collecting gluetool
  Using cached gluetool-1.25-py3-none-any.whl (302 kB)
  Using cached gluetool-1.24-py3-none-any.whl
  Using cached gluetool-1.23-py3-none-any.whl
  Downloading gluetool-1.22.tar.gz (300 kB)
     |████████████████████████████████| 300 kB 2.0 MB/s 
  Downloading gluetool-1.21.tar.gz (300 kB)
     |████████████████████████████████| 300 kB 2.1 MB/s 
  Downloading gluetool-1.20.tar.gz (300 kB)
     |████████████████████████████████| 300 kB 2.1 MB/s 
  Downloading gluetool-1.19.1.tar.gz (297 kB)
     |████████████████████████████████| 297 kB 4.7 MB/s 
  Downloading gluetool-1.19.tar.gz (297 kB)
     |████████████████████████████████| 297 kB 4.1 MB/s 
    ERROR: Command errored out with exit status 1:
     command: /home/mvadkert/temp/venv/bin/python3 -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-yfughhi9/gluetool_cf00d22ad59e43f395baf9987896ae1c/setup.py'"'"'; __file__='"'"'/tmp/pip-install-yfughhi9/gluetool_cf00d22ad59e43f395baf9987896ae1c/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-_8h4ho7l
         cwd: /tmp/pip-install-yfughhi9/gluetool_cf00d22ad59e43f395baf9987896ae1c/
    Complete output (6 lines):
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-install-yfughhi9/gluetool_cf00d22ad59e43f395baf9987896ae1c/setup.py", line 11
        print 'Failed to extract version tag: {}'.format(exc)
                                                ^
    SyntaxError: invalid syntax
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

[teddyward]

I have a LOT of new things that fail with pip >= 20.3. Most particularly:

1. having dependencies with >= or <= or * now install every available version that matches the text. e.g. having Django==2.2.* installs every patched version of django 2.2
2. dependency conflicts that previously succeeded like us==1.0.0 jellyfish==0.6.1 now fail

[uranusjr]

Duplicate to #9246.