Support pixi as an install tool

[jaimergp]

Checklist

• Added a news entry
• Regenerated schema JSON if schema altered (python conda_smithy/schema.py)

Only an experiment for now. Testing at conda-forge/dav1d-feedstock#21.

Will close conda-forge/conda-forge.github.io#2323.

[jaimergp]

This is mostly functional. See last runs at conda-forge/dav1d-feedstock#21.

It provisions the base environment in a similar way to what micromamba does, but the dependency list is coming from the pixi.toml file. Since we have to populate that anyway, I also rendered a few convenience tasks for local users, so they can just do pixi run build, pixi run rerender, etc. Not perfect or a 1:1 correspondence to CI (for that they have pixi run build-locally), but a first approach to see how it feels.

To note:

• The installation paths do not correspond 1:1 either, but the "spirit" is there; e.g. on Windows we respect the drives so we get all the performance gains from D:.
• There's an ugly hack to limit which platforms get solved in CI (we patch platforms in the TOML file), but hopefully that'll get added soon in Pixi so we just use a flag like --platforms=linux-64 for overrides.
• Pixi doesn't seem to offer PowerPC binaries? nvm: enable ppc64le pixi-feedstock#78

Anyway, fun stuff! The linux timings are impressive; around 10s thanks to the shared pkgs cache. macOS and Windows stay under a minute.

If this is considered for merge, I'd leave it as opt-in for now, so folks can experiment on their feedstocks and go back to micromamba if needed. Happy to add a warning or something to consider it "experimental" too.

conda-forge/staged-recipes#27754 is the equivalent PR in staged-recipes.

[beckermr]

The handling of local_ci_setup might be flawed right now IIUIC.

The current procedure on main installs the conda package, then force uninstalls it to leave the deps in the env, and then does the pip install without deps.

The code in this PR does a pip install on top of the conda package.

IDK if those two things are equivalent.

We should test this in the ci-setup feedstock.

[jaimergp]

Agreed, I haven't tested that, mostly left it there as a reminder of sorts. Worst case conda-forge-ci-setup can stay with conda_install_tool = "micromamba". Let me give it a try in the feedstock though.

[jaimergp]

See conda-forge/conda-forge-ci-setup-feedstock#361 for ci-setup tests.

[beckermr]

LGMT to me assuming all of the feedstock tests work. I've been merging a bit fast I think since I've seen a few comments on PRs after I have merged them here. So i'll bump @conda-forge/core to look at this one too.

[jaimergp]

No probs, thank you for the reviews! I'm in no rush here, was just following the momentum of the micromamba changes because I had all that mental model in the "hot cache" part of my brain :P

For those checking the PR now or later, this comment summarizes the changes: #2099 (comment).

[h-vetinari]

Haven't reviewed, but I think this is a great initiative and thanks a lot for pushing it forward. I checked out conda-forge/dav1d-feedstock#21 and I think it's really cool (aside from the speed gains) that with pixi tasks, we'll provide a much simplified interface for building things locally, e.g. pixi run build-linux_64_. 😎

[mfisher87]

we'll provide a much simplified interface for building things locally, e.g. pixi run build-linux_64_

Oooo... amazing! I love that re-rendering is now a task, too!

[beckermr]

@conda-forge/core it has been two weeks on this PR and there are no other reviews. Shall we merge?