Build fails with python_min is undefined in PRs with multiple packages

[Saransh-cpp]

Bug:

At the moment, you can skip specifying set python_min... at the top of the yaml file if your package is strictly not Python 3.10+, but the CI fails if -

1. you do not specify the value for python_min, and
2. your PR has multiple interdependent packages.

After some digging, I am confident that the failure does not depend on the presence or absence of noarch, instead, it happens with every PR having multiple packages. For instance, see the failures and discussions in #28405 and #28431.

cc: @conda-forge/staged-recipes

[d70-t]

I don't have a full explanation for this yet, but this might be a clue: if I understood this correctly, the metadata are rendered using this function:

staged-recipes/.ci_support/compute_build_graph.py

Line 221 in eba9275

def _get_or_render_metadata(meta_file_or_recipe_dir, worker, finalize, config=None):

Now _get_or_render_metadata can be called from two different sites, depending wether the rendering is triggered through an actual build, or just the check if it is buildable, e.g. in case there are two newly added packages packages A and B, where A depends on B. If A is attempted to be built first, the build script for A will try to determine if B could be built. In this case, it will render the metadata for B though the _buildable function.

Now remarkably when _get_or_render_metadata is called from _buildable, there's no config argument passed along:

staged-recipes/.ci_support/compute_build_graph.py

Line 455 in eba9275

for (m, _, _) in _get_or_render_metadata(os.path.join(recipes_dir,

whereas when _get_or_render_metadata is called from add_recipe_to_graph, there is a config argument:

staged-recipes/.ci_support/compute_build_graph.py

Line 238 in eba9275

rendered = _get_or_render_metadata(recipe_dir, worker, config=config, finalize=finalize)

I didn't yet figure out if this missing config argument is where python_min would have to be passed though...