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