File a bug with Rust/Cargo requesting the ability to ship a target.json in a crate

[alex]

No description provided.

[geofft]

It looks like the ability to ship / install arbitrary resources in crates is rust-lang/cargo#2729 and rust-lang/rfcs#2376 (both still open). The latter is specifically about installing things; the former seems to also encompass resources used by the application. You can already include arbitrary files in your crate (via includes in Cargo.toml) but they only end up in the crate source package, i.e., they're only really useful for build scripts or include_str! or similar.

I looked a bit at whether it's possible to implement this in cargo via a new build script option, like cargo:rustc-target-json={"disable-redzone": true, ...}. But then I realized that if that's doable, it should be possible to implement this already by having the linux_kernel_module build script create the target.json file inside $OUT_DIR, and then print cargo:rustc-env=RUST_TARGET_PATH=....

That doesn't work, because cargo wants to have the target config already in place when it starts up, so that it can find out the names of output files (it runs rustc --print=file-names and appends a --target option if you specify one), even before it runs the build scripts. I'm not totally sure why it needs this, but there is probably a good reason and changing it is likely to be hard.

So, I think if this is going to work, it's going to need to pull the target specification out of the sources. I think this is reasonably easy: there's a cargo metadata command, and you can just go through dirname(i['manifest_path']) for i in metadata['packages'] and see if any of those have the target.json. cargo metadata doesn't even take a --target argument, so it definitely works.

This could happen either in cargo-xbuild or cargo itself ... it's probably an easy source-level change in cargo, but it's definitely doable from cargo-xbuild too.

[alex]

This is being obviated by simply upstreaming the target files.