PyPy compatibility

We are trying to use setup-miniconda to enable PyPy CI pipelines in https://github.com/openmm/openmm/pull/3086, but we are facing some issues with the python-version option. Seems that the action adds python=x.y to the environment, and that causes some issues if python_abi=pypy.

I am going to run some tests locally, but in the meantime I am wondering if people have run into the same issue.

I will document my progress here because setting pypy is not very straightforward right now and we might need to document it.

[bollwyvl]

docs sounds simple…

`python-version` may be either:
- a simple version number like `3.9`, which will have a `=` inserted, yielding `python=3.9`
- a full [conda spec][], e.g. `=3.7[build=*_pypy]`, which will be used as-is, yielding `python=3.7[build=*_pypy]`

[conda spec]: https://docs.conda.io/projects/conda-build/en/latest/resources/package-spec.html#package-match-specifications

[bollwyvl]

re: adding an “extra” python: i thought it would try to remove the original spec, but perhaps it does not.

re: conda-lock for patching, etc: it accepts a variable number of --file arguments: for example, this set of envs generates this set of locks, doing some permutations off task name, os, gpu/cpu, etc. I like to have them checked in for long-term analysis (and because the build takes for-frigging-ever already) and offline testing, but there’s nothing that requires that.

re: removing: If anything, getting a --not-file added to conda-lock might make it easier, but frankly i haven’t yet minded it being additive-only. I guess I had had the conda-lock behavior in mind when bringing this feature in, that it would be additive-only, as there is no conda spec for “but without this”… other than run_constrained, and that’s only available in meta.yaml.

I think once we get to this level of complexity, however, I’d pretty much not want to re-invent the wheel in typescript: if environment-files was an input, we’d just install conda-lock in the base env (much like conda-build-version), build the lockfile, and then re-use the explicit provider. the lockfile content/path could then become an output, which could drive caching, which would be quite nice.

I don’t know if either conda/mamba would want to make the first move on supporting multiple files or “but-not-this” specs… and we’re still learning what it really means on conda-lock.