Urg, the Pip legacy resolver has regressed wrt constraints files. If the constraints file contains any requirements not in the resolved set (which will ~always be the case for Pants use) it raises an AssertionError. Using the 2020-resolver all is well. I did not want to mix the Pex upgrade with switching the resolver too.

Alright, I think the only thing to do here is file an issue / fix PR against Pip and then update the pantsbuild/pip fork with the same PR and have Pex use that for a bit 😕.

I have https://github.com/pypa/pip/pull/9301 away to fix this issue in Pip, but I'm pessimistically moving ahead with https://github.com/pantsbuild/pip/pull/8 to allow a release of Pex against a patched version of Pip 20.3.* until / if Pip resolves the issue.

does that help here?

They introduced a regression - works fine in new resolver.

🚢 for https://github.com/pantsbuild/pip/pull/8

let me know if there is anything i can do to help. will hold off on all releases right now.

https://github.com/pantsbuild/pants/pull/11317 is the last one for the 1.30.x branch. That was totally manual - not a cherry-pick.

And 1.30.x is almost surely going to bleed into tomorrow. I'm happy to deal with that release @witty-crayon-22786