Docs not built on target platform, causing failures

[CamJN]

Crate name

getargv

Build failure link

https://docs.rs/crate/getargv/0.1.1/builds/701636

Additional details

This crate has a dep getargv-sys which requires an apple OS to build, I specify:

[package.metadata.docs.rs]
targets = ["x86_64-apple-darwin", "aarch64-apple-darwin"]

In both crates' Cargo.toml; but when docs.rs builds the getargv crate, the getargv-sys crate is built with an incompatible system/command.

[CamJN]

Actually I just checked and it fails to build getargv-sys directly too... I see in the log that the build command has the "--target" "x86_64-apple-darwin" flag, but does it actually do anything? the build script still seems to know it's not an apple OS.

[CamJN]

I can detect building in docs.rs and bypass the OS check, but the sys/types.h header will be wrong on a non-apple OS so the generated docs will probably be wrong.

[CamJN]

not mine but i noticed https://docs.rs/crate/mac-notification-sys/0.5.6 is broken too since docs.rs doesn't build macOS sys crates on macOS, and i imagine there are others too.

[syphar]

Thank you for the report!

Docs.rs currently only builds x86_64-unknown-linux-gnu natively and uses cross-compilation for all other targets (see here).

I see you fixed this (e.g. worked around the limitation) for getargv and getargv-sys already, does this mean this issue is solved for you?

Building on native targets is a bigger topic and not easily solveable right now.

[CamJN]

Yeah I made it build, but I had to shim in a header, and I was wondering what the current advice is for bindgen based crates on non-linux platforms?

I'm also still a bit confused why cfg!(not(target_vendor = "apple")) does not reflect the target triple set with the --target flag in the build command.

[Nemo157]

I'm also still a bit confused why cfg!(not(target_vendor = "apple")) does not reflect the target triple set with the --target flag in the build command.

The build script is always built for the host, which is what cfg! checks; if you want to know what target it is being run for you need to inspect the environment variable CARGO_CFG_TARGET_VENDOR while it is running.

[jyn514]

potential mis-compilation of docs

I think this bit is not true, the cfg was set correctly, the build script was just interpreting it wrong.

[CamJN]

@jyn514 it can very much cause miscompilation. If you run bindgen on the wrong platform it might pick up a header with a type defined for say x86 linux instead of aarch64 macOS, which would result in mistakes in the generated docs.

[jyn514]

@CamJN that sounds like a bug in bindgen, that would break when cross-compiling as well.

[CamJN]

Cross compiling anything that links to C requires you to have all of the C headers of the target installed. Bindgen supports this fine by allowing you to specify where to look for C stdlib headers, your environment does not provide these things, so cross compiling does not work properly.

[CamJN]

If you'd like some docs on how to get the headers this does a decent job of explaining what's required: https://github.com/tpoechtrager/osxcross#packaging-the-sdk