Building crates that work only on some platforms

[Boddlnagg]

Crates such as https://docs.rs/crate/core-foundation/0.4.1/builds fail to build on platforms other than macOS. In this case, it fails with error: native frameworks are only available on macOS targets, but the crate would build correctly on macOS targets ... docs.rs doesn't seem to even try to build on macOS, however, after this error.

Could it be changed in such a way that docs.rs tries to build on all platforms and later only show the subset of platforms where it succeeded to build?

[onur]

This is a known limitation of docs.rs.

Docs.rs is only using a Linux host machine right now. I can implement building on OSX if someone donates an OSX server.

[Boddlnagg]

Huh? But I changed coremidi-sys in such a way that it would be cfg'ed out if the target is not macOS, so it would not result in the linking error, but instead just build an empty crate. This worked, I can see the documentation for macOS: https://docs.rs/coremidi-sys/2.0.2/x86_64-apple-darwin/coremidi_sys/. (Note that it did not work before the change: https://docs.rs/crate/coremidi-sys/2.0.0/builds)

So this means that somehow building for macOS target does work, and docs.rs should do that even if the build for other targets fails.

[onur]

Ahh I see, I thought OSX targeted crates requires an OSX host machine, but looks like they are like winapi crates and rust-std for OSX is enough to build this type of crates.

Yes, I agree docs.rs should try to build crates for all targets and decide default-target itself. This is a neat idea and thanks for suggestion. I'll see what I can do.

[Boddlnagg]

Thanks, that sounds great! 👍

[jrmuizel]

I've run into this as well. What would be the best way to implement this?

[quadrupleslap]

Can I do anything to help get this implemented? I haven't looked too closely, but it looks like src/docbuilder/chroot_builder.rs is the only file that needs to be changed.

Edit

I skimmed over the source, and it looks like there's a 'main' build in the way Docs.rs is implemented, and right now that build is the one for the current platform. It looks like the two ways to address this issue would be to:

1. Modify build_package_in_chroot to use the default-target from the metadata if it is provided, so that the user gets to choose which platform this 'main' build happens on. This looks easy to implement, and should be enough.
2. Get rid of the idea of a 'main' build, and just build it on all supported platforms, saying that there was a build error only if it failed on all platforms. Also, try to guess the default-target by looking at which platforms succeeded. This looks harder to implement, but I guess this is the more 'elegant' solution.

I think makes sense to implement (1) and then later implement (2).

Sorry if I said anything obviously stupid.

[jyn514]

I'm actually hoping to go the other way and only build one target unless requested otherwise, see #532.

Would setting default-target to x86_64-apple-darwin fix your problem? We no longer ignore this field, winapi for example uses it since their builds only work on Windows.

[jrmuizel]

Yes. I think that should work.