Returning a RequirementSet from Resolver.resolve

Description Currently, pip’s Resolver.resolve method is expected to mutate the RequirementSet provided to it; which results in a slightly difficult to follow control flow.

Desired behavior

Resolver.resolve(req_set: RequirementSet) -> RequirementSet

Known Challenges pip’s install, download and wheel commands, have a requirement_set.cleanup_files() call in a try-finally, which means that the existing requirement set is clearly assumed to be the only one that exists. We’d likely want to construct a new set in the new resolver, so figuring out how we’d handle cleanups is the main thing to do here.

[pfmoore]

I’ve unassigned myself from this because I’m struggling to understand what it actually means. I get the broader goal of improving the control flow, and decoupling “before the resolve” from “after the resolve”, but I’m not clear how this specific change would work in that context. So rather than block someone else from looking at it, I’ve unassigned myself.

[chrahunt]

why would the resolver result need to include a “force install” option?

It wouldn’t need to, you’re right. As long as we enrich the resolver result with information indicating that some of the things already installed will need to be force-reinstalled then I think that’s good enough. The resolver doesn’t need to know about a “force install” option. Above I was imagining it from the perspective of a function that would take a “resolver result” (and an install scheme) and do the required installations with no other input.

The resolver just returns a list of what resolvelib calls “Candidates” - essentially project name and version.

In my view the resolver will return Projects (or some wrapper around them), or objects that we use as an index into a lookup table of the Projects that have been used during the resolution process.

The rest of your statements sound reasonable to me.