TARGET in build.rs is invalid

[berkus]

When using a full path to json file as cargo-xbuild --target argument, the resulting TARGET is not a triple but instead a full file path. I believe it should be a triple.

According to cargo book:

TARGET - the target triple that is being compiled for. Native code should be compiled for this triple.

What I'm getting:

λ cargo xbuild --target=targets/aarch64-vesper-metta.json
   Compiling vesper v1.0.0 (/path/to/vesper)
error: failed to run custom build command for `vesper v1.0.0 (/path/to/vesper)`
process didn't exit successfully: `/path/to/vesper/target/debug/build/vesper-6432e1d623b2c988/build-script-build` (exit code: 101)
--- stderr
Target /path/to/vesper/targets/aarch64-vesper-metta.json
thread 'main' panicked at 'TARGET env variable is not set to one of supported values', build.rs:43:9

The line Target /path/to/vesper/targets/aarch64-vesper-metta.json is output by build.rs from the TARGET env var.

[phil-opp]

Seems like the cargo documentation is not specific enough or out of date. A target triple in rust can be either a triple string or a path to a JSON file: https://github.com/rust-lang/rust/blob/653da4fd006c97625247acd7e076d0782cdc149b/src/librustc_target/spec/mod.rs#L1275-L1278

[berkus]

Hmm, ok, still very inconvenient because my build.rs only need to look at the TRIPLE regardless of actual json file path.

Can this be added? Maybe even to cargo? (As TARGET_TRIPLE for example)

Basically this means I just need result of calling triple() on the triple, so I can probably construct it from the envvar and then call the triple() function, let me try that.

[berkus]

Probably it makes more sense to match on (CARGO_CFG_TARGET_ARCH, CARGO_CFG_TARGET_OS, CARGO_CFG_TARGET_FAMILY) triple instead.

[phil-opp]

You could use https://doc.rust-lang.org/std/path/struct.Path.html#method.file_stem to get the triple from a path.

[berkus]

I used direct match on the env vars and it worked excellently!

[phil-opp]

Cool!