recipe pins appear to be implemented incorrectly relative to conda-build

[beckermr]

It appears that for a bit of yaml like this

requirements
  run:
    - python ${{ python_min }}

with python_min=3.10, rattler produces a different spec than conda-build.

For rattler-build, I see

requirements:
  run:
    - python ==3.10

See this CI job (https://dev.azure.com/conda-forge/feedstock-builds/_build/results?buildId=1075636&view=logs&jobId=7b6f2c87-f3a7-5133-8d84-7c03a75d9dfc&j=7b6f2c87-f3a7-5133-8d84-7c03a75d9dfc&t=9eb77fd2-8ddd-5444-8fc0-71cb28dcb736)

conda-build adds an implicit .* like this

requirements:
  run:
    - python 3.10.*

For a pin like 3.10, the net effect of .* for conda-build is to pull the latest version that is less than the next minor version (i.e., 3.11.0). An equivalent syntax, I think, is python =3.10 (i.e., a single =). rattler-build could use a single = if it does not handle .*

[wolfv]

Can we just put "3.10.*" for the least ambiguous syntax?

[beckermr]

Sure! I just didn't know if rattler-build supported that.

[rgommers]

Rendering a recipe using python_min now seems to yield this complaint:

 26 │     - python ${{ python_min }}
    ·       ────────────┬───────────
    ·                   ╰── This match spec is ambiguous. Do you mean `python ==3.9` or `python 3.9.*`?

That is better than silently using 3.9.0, but still bad - the 3.9 is defined by conda-forge, and it shouldn't have to be overridden in every recipe.yaml. That would also defeat the purpose of the whole exercise, so unless conda-forge wants to update the 3.9.* now (does that work with conda-build?) there is an issue.

Either way it seem much better to make this work as expected in rattler-build; using a specifier like 3.9 is very common in both conda and python metadata file, and people always mean .* and never .0.

[beckermr]

Yep. There are a lot of strong opinions floating around on these specific issues. We're not going to resolve them until we write and vote on a CEP that defines the correct behavior.