`CARGO_CFG_TARGET_FEATURE` does not include default value of `crt-static`

[madsmtm]

Problem

The value of target_feature = "crt-static" can be controlled in rustc with -Ctarget-feature=+crt-static or -Ctarget-feature=-crt-static. Some targets have this enabled by default, but that doesn't seem to be propagated to CARGO_CFG_TARGET_FEATURE.

Steps

Create a build script with the following contents:

fn main() {
    println!("cargo::warning={:?}", std::env::var("CARGO_CFG_TARGET_FEATURE"));
}

Since running rustc --target=aarch64-unknown-linux-musl --print=cfg outputs target_feature="crt-static", one would expect it to also be output with cargo check --target=aarch64-unknown-linux-musl of the above program, but it does not, setting RUSTFLAGS="-Ctarget-features=+crt-static" is required.

Possible Solution(s)

Maybe this method in rustc needs to be tweaked?

Or maybe Cargo needs to avoid passing --crate-type proc-macro to rustc when determining target info? (somewhere around here)

Notes

This is somewhat affecting cc, as it is not guaranteed to pass the correct value for the ``/-static flag to compilers (though it shouldn't matter much since `cc` doesn't link anyhow).

Version

cargo 1.84.0-nightly (cf53cc5 2024-10-18)
release: 1.84.0-nightly
commit-hash: cf53cc5
commit-date: 2024-10-18
host: aarch64-apple-darwin
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.7.1 (sys:0.4.74+curl-8.9.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w 11 Sep 2023
os: Mac OS 14.7.0 [64-bit]

[ehuss]

Hm. We really need a better way to query rustc for information¹. In this particular case, I would lean towards finding a new way to get information from rustc about the supported crate types and the output file prefix/suffix without using --crate-type.

Footnotes

1. I would like to be able to run a single rustc invocation that will spit out a single JSON blob with all the information we need, instead of the text-based parsing system we have now. ↩