PackagingWG/2020-02-17-pip

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Resolver meeting

17 Feb 2020

Participants: Paul, Pradyun, Tzu-Ping

Some initial thoughts:

  • Existing upgrade strategies may not map nicely to new resolver

    • Define new upgrade strategies that match new resolver ideas

    • For new resolver, map existing strategies to “best fit” new ones as aliases

    • Deprecate old strategies when used with new resolver (longer term)

  • Without --upgrade{.backtick}, we can just return installed versions as the only candidate in find_distributions{.backtick}

    • Will make the solve faster, but might make reporting more difficult

    • Cargo(?) does a two-pass resolution, the second pass only to collect errors. Could be a good idea?

  • Maybe possible to do similar for other options/upgrade strategies?

Two scenarios:

  • I want to upgrade this, do the minimal possible to make it work

    • This is usually what people want when they pip install -U{.backtick} globally

  • “Upgrade all” (which pip does not have right now)

    • This is usually what people want when they pip install -U{.backtick} in a virtualenv

  • pip install -U foo

    • Tells pip “Try what you need to make this work”

    • Implication: If this can’t work, error out

    • pip can suggest pip install -U foo bar{.backtick} when it errors out to help the user

    • don’t automatically upgrade going “up” the dependency graph.

* Add a new –upgrade-strategy that is even more conservative than only-if-needed that reports (instead of upgrade) if pip needs to upgrade

  • Probably doesn’t need to, it’s the user’s responsibility

iterating on upgrade strategies

–no-deps: for people doing resolution externally to pip

Environment metadata issues:

  • No information about “requested” extras

    REQUESTED (https://www.python.org/dev/peps/pep-0376/#requested)

    • Pradyun: I want to flip the file, to indicate “i was automatically installed”

      • Marking existing installed packages as “requested”.

      • Trimming installed-as-dependency packages.

    Pradyun: How about we combine them both? “REQUESTED” serves as our manifest