First stab at implementing the resolver provider using pip internals

[uranusjr]

This is not intended to be merged, but posted to raise awareness and discussions.

I went through a few iterations on this, but couldn’t really figure out how to directly use InstallRequirement, so right now I am using Requirement from packaging, InstallationCandidate returned by the finder, and some custom PODs to do the job. I implemented the straightforward parts, but the most hairy one awaits: Read metadata from a random candidate (for version and dependencies).

cc @pfmoore

[pfmoore]

Nice. See my post on zulip for some code snippets that would help here. I'll see if I can integrate those into what you have.

[pfmoore]

Some further comments.

It would be nice to have a simple unit test that ensured this was callable somehow. I'll look at writing one. I don't know what the best way is to develop code based on someone else's PR, though. For now I'll develop locally on a branch based off your PR, but we should work out how to share that code, and how to merge any useful changes into your PR.

[pfmoore]

We're working in very close to the same areas of code at the moment, and it'll be easy for us to overlap (see my latest round of comments, which were partially outdated immediately after I posted them because I hadn't refreshed my browser!)

We should discuss how to avoid clashing at today's meeting. But for now I'll work on looking at how we can write some tests for these new classes. That should avoid me duplicating what you are doing too directly.

[pfmoore]

What's the best way to share my code? I don't know how to write a PR based on another PR... 😕

Edit: Just noticed the comment below, "Add more commits by pushing to the provider-integration branch on uranusjr/pip". I guess that answers my question - I can do PRs against your repo/branch. Does that seem OK?

[uranusjr]

I can do PRs against your repo/branch. Does that seem OK?

Yup definitely, go ahead 👍

[uranusjr]

And if you can’t, just push this branch to pypa/pip instead. I think I can commit to non-protected branches (i.e. other than master).

[pfmoore]

Hmm, I'm getting in a mess here :-(

Given that I have a clone of https://github.com/pfmoore/pip, with a remote called "upstream" pointing at https://github.com/pypa/pip, how do I:

1. Check out your PR? At the moment I have an alias (picked up from somewhere) that does git fetch upstream pull/${1}/head:pr_${1} && git checkout pr_${1}. That gives me a pr_7789 branch, but I don't know how to pull updates to the PR into it.
2. Make changes so that I can push them back somewhere, and still pull/merge your changes to the PR?

I suspect what I should do is create a new uranusjr remote, and pull your branch from there and branch off that. Is that right? git pull uranusjr provider-integration; git checkout uranusjr/provider-integration; git checkout -b my_fixes?

Sorry if this is all basic, I've never needed to do anything more complex than "create a PR" workflow with git before...

Also, unrelated, but I've created a couple of new test fixtures. To keep them separate, I put them in tests.lib.pip_api_helpers, but if I do that I need to import them in test files, and flake8 then complains about unused imports and shadowing redefinitions. If I import them in conftest.py, I get an unused import error there. If I don't import them, I can't use them 🙁 What's the best fix? A noqa marker? Or give up and implement them in conftest.py?

[pradyunsg]

1. git fetch upstream pull/${1}/head:pr_${1} && git checkout pr_${1}

One of the things with this is that GitHub's pull/ references are read only.

[uranusjr]

Let’s just push to pypa/pip instead, I believe all of us have permission to do that. (I hate permission stuff.)

[uranusjr]

Moving to #7799.