Testdrive cargo-zig for cross-compilation

[sureshjoshi]

I’ve been messing around locally, and there are some PyO3 cross-compilation things to figure out, but this could de-couple us from needing to build natively per-platform in CI (though, we probably still would want to for testing purposes).

At the very least, we could decouple from ubuntu versions due to shipped libc

[jsirois]

I think you know you have this example, but that's what I do over in pexrc and its lovely. I found by experiment that the ubuntu-24.04-arm runners were fastest free GitHub hosted runners; so I just build for all 12 target platforms (8 Linux, 2 Mac, 2 Windows) from arm Linux. As you point out the ability to pick ~any glibc is freeing. I have some custom config here for that that the build.rs reads to create .{glibc_version} target extensions to pass to zigbuild: https://github.com/pex-tool/pexrc/blob/6f1d37d1bbcd33a88e4f82e8c73a1a60b440c789/Cargo.toml#L50-L63

[sureshjoshi]

Sweet, thanks John! And yeah, I was checking out pexrc by way of example earlier today.

[jsirois]

The pexrc build is complicated since each pexrc binary must embed a shared library per supported target platform (currently 8.so / 2 .dylib / 2 .dll) so I have a custom build.rs and then a custom package crate on top of that. You should just be able to cargo zigbuild --target aarch64-unknown-linux-gnu.2.17 (for example) in CI and be done with it mod the PyO3 weirdness - which is, I suspect, the need to have a native CPython (or its headers) to link against or some such.

[sureshjoshi]

I spent last night getting my linux box to compile to Mac, but then got steamrolled by this in the end. There are some quirks when building aws-lc-rs (aws/aws-lc-rs#512), but the more surprising part was running into this segfault a few times (https://codeberg.org/ziglang/zig/issues/31189), and the even more surprising part was having this happen in a container and take down my computer... That's not something you see everyday on Linux.

I put up a work-in-progress here: https://github.com/pantsbuild/pants/blob/cargo-zig/.github/workflows/release-zigged.yaml and will mess around with compiling from mac-arm instead, which should bypass some of these compilation issues.

This is very much the "does it compile" step, not the "does anything actually work" step.

[sureshjoshi]

Blah, still fails to compile MacOS when compiling with macos. Zig fails to link, without much in the way of errors - so it might be the seg fault.