Compatible versions of pip-tools and pip

[atugushev]

Since old pip versions are dropped (see #926) it would be useful to have a section in README which would help users find the version of pip-tools with support for a specific version of pip. It could be a table, for the instance:

• pip-tools<=4.5.* compatible with pip>=8.1.1,<=20.0.*
• pip-tools==5.0.* compatible with pip>=20.0,<=20.1.*
• pip-tools==5.1.* compatible with pip>=20.1,<=20.2.*
• pip-tools==5.2.* compatible with pip>=20.2.*
• etc ...

Originally posted by @atugushev in #926 (comment)

[adamchainz]

It would also be good to have a runtime check that the current version is compatible with the current pip. One gets odd errors otherwise.

[atugushev]

@adamchainz that makes sense. Actually, we had this check before. See 2a21f6e.

[adamchainz]

Cool. Any idea why it was removed?

[atugushev]

@adamchainz it was removed later because of pip vendoring.

[atugushev]

On the other hand, the default failure message is pretty informative.

$ pip install pip==19.3.1

$ pip-compile
Traceback (most recent call last):
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 584, in _build_master
    ws.require(__requires__)
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 901, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 792, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.ContextualVersionConflict: (pip 19.3.1 (/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages), Requirement.parse('pip>=20.0'), {'pip-tools'})

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/albert/Projects/pip-tools/.venv/bin/pip-compile", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3254, in <module>
    def _initialize_master_working_set():
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3237, in _call_aside
    f(*args, **kwargs)
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3266, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 586, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 599, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/Users/albert/Projects/pip-tools/.venv/lib/python3.8/site-packages/pkg_resources/__init__.py", line 787, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'pip>=20.0' distribution was not found and is required by pip-tools

[adamchainz]

Thanks @atugushev

Yes the error message is informative. I think the case I saw with odd runtime errors was with an old pip, python, or pip-tools version.