osx_arm64: more detailed instructions

[MarDiehl]

Where should the content be added?

https://conda-forge.org/docs/maintainer/knowledge_base.html

What should be added?

I could not find detailed instructions for adding osx-arm64 support for an MPI package and succeeded only with the help of @isuruf. Some information is available on

• https://conda-forge.org/docs/maintainer/knowledge_base.html#cross-compilation
• https://conda-forge.org/blog/posts/2020-10-29-macos-arm64

An related issue is #1534, which also mentions a migrator (https://github.com/conda-forge/conda-forge-pinning-feedstock/blob/master/recipe/migrations/osx_arm64.txt).

There are two routes for an improved documentation: Either have add an extra section on (cross)-compiling for osx-arm64 or add content to https://conda-forge.org/docs/maintainer/knowledge_base.html#cross-compilation and https://conda-forge.org/docs/maintainer/knowledge_base.html#message-passing-interface-mpi. This should be consistent with the approach for other non-default architectures.

Additional information

Content of the documentation

• https://conda-forge.org/blog/posts/2020-10-29-macos-arm64 is a good starting point, most of it should become part of the official documentation to emphasize that this is the current state and not just an potentially outdated blog post.
• for https://github.com/conda-forge/libfyaml-feedstock (autotools) cp $BUILD_PREFIX/share/gnuconfig/config.* . was not required.
• build requirement for mpi: openmpi # [mpi == 'openmpi' and build_platform != target_platform] (with explicit explanation why openMPI and MPICH behave differently).

[jaimergp]

Excellent timing, @MarDiehl!

@FFY00 is currently documenting how different ecosystems approach cross-compilation in Python projects in PEP720 (draft) and I've been instructed to compile some info about how we do things over here.

As you can see, conda-forge's strategy is not fully documented so this is a good time to revisit and consolidate how we are doing things. I for one don't know too much about all the business concerning crossenv, even after reading the blog post or the PEP.

I'd like to ask folks to help me understand and collaborate in writing something we can refer to officially. I will do some more reading and start a PR soon.

Tagging @conda-forge/core for awareness.

[jaimergp]

Hi again! I started a PR at #1985. Hopefully we can all collaborate there to have better documentation around cross-compilation!