"universal2" and alternate deployment target on macOS

[ronaldoussoren]

Platform: macOS, in particular M1 systems.

These systems can run both arm64 (native) and x86_64 (in emulation) code, with per process selection using the "arch" command.

For C extensions it is possible to build both architectures on an M1 system (basically a form of cross compiling), including merging code for the two architectures in a fat binary ("Universal 2" in Apple-speak).

setuptools_rust will currently always build arm64 code only, even if python was started in x86_64 mode (e.g. arch -x86_64 python3.9 setup.py build_ext).

It would be nice if setuptools_rust were able to build "universal2" wheels.

An related to this: for C extensions Python by default builds extension that work on the deployment target used for the python binary. It might be necessary to enhance setuptools_rust to do something similar.

BTW. I hope to have some time to work on a PR in the near future.

[davidhewitt]

Thanks for reporting. If you are able to find the time, a PR to help with this would be very much appreciated.

I took a quick look just now and it looks like upstream support is possible; we'd probably need to build both targets separately and then invoke macOS sdk tools to build the final library. I'm inferring that from BurntSushi/ripgrep#1737

[davidhewitt]

Also see PyO3/maturin#405