Resolver Dev Syncup (22 April 2020)

Participants: Paul, Pradyun, Tzu-ping

Agenda

- Goals

• When will we be "done"?
  • Paul: IMO, the first key milestone is when all the tests pass. After that, I think depends on user survey feedback.
  • Paul: Also, how does "when all the tests pass" link to Ilan's work? Do we expect him to deliver new tests for additional resolution scenarios? I thought he was going to...
  • Pradyun: I think we do, yea. There's a whole bunch of issues we've got in zazo's issue tracker, that really need to move into a YAML test.

- Remaining functionality (prioritization)

• (from last week)

  • user installs (may be solved by https://github.com/pypa/pip/pull/7997 )

  • upgrade strategy (need to emit a warning/error for this)

    • TP: I want to replace it with a new flag --strategy ( https://github.com/pypa/pip/issues/8085 )

    • Two existing, plus "install minimum possible version". Implement the mechanism, decide on how to expose it later.
      • "install minimum possible version" -- new feature, not on roadmap for resolver, may never happen :P
  • constraints (has error message)

  • wheel cache ( https://github.com/pypa/pip/pull/8066 )

  • error messages (see below)
  • circular dependency (has error message)

General principle, we should implement the mechanisms and leave UX for follow-up discussions.

"What are we allowed to upgrade":

• - Internal inconsistencies in what the user asks for - just reject (easy) - Request conflicts with what's installed, and no --upgrade flag - can just reject as well - When we can upgrade, --upgrade is too blunt a tool, we need to know *what* we are allowed to upgrade
  • - Initially, pass into the API a list of individual packages we're allowed to upgrade. Work out how to present that as a UI later

Everyone likes XPath we should do more of that! (NOT!!!!)

Talked about hypothesis for testing the resolver / resolvelib.

Talked about tests

• Slowness
  • Get to upgrade to virtualenv 20
• Caching wheels generated during tests -- for Windows antivirus!!!
• TODO: TP to write short summary on importlib-metadata thing and explain what he wants, maybe the GSoC student can help on the work.
• Windows CI boxes: do they allow symlinks?
  • TODO: Need to check this (Pradyun).

  • https://python.zulipchat.com/#narrow/stream/218659-pip-development/topic/Resolver.20and.20Testing/near/193347324

- Error messages

• Paul getting frustrated at the complexity of the problem.
• Need more points of contact / discussions with UX team would be good.

• Talked about https://pypistats.org/packages/pip, and how sharing it with the UX folks helped

- Visualizing graph exploration

• Pradyun spent some time on this -- got tied up in other work, so it's on the back burner

- Augumenting REQUESTED as a distributed MANIFEST

• Store some decomposed form of a requirement?
• Whatever we come up with in the [metadata] table discussion?

- PEP 610 + new resolver ( https://github.com/pypa/pip/pull/8005 )

- Broader discussions:

• pip inspect: bundle together all environment introspection functionality into a single command.

  • pip check, pip list, pip freeze, pip show
  • new feature requests we've seen: "tree view"
  • Pradyun: [describes the above]
  • Paul: Makes sense.
  • Tzu-Ping: Makes sense.
  • Paul: We can probably do something similar to this for pip's index interaction stuff.

    • Pradyun: That's TP's proposal for a 'pip discover' command! We can make something like pip index for that!

• Talked about pip wheel
  • Let Paul come up with a paragraph to redescribe what wheel does and fix the docs and the command description

• pip search: https://github.com/pypa/pip/issues/5216