cargo build --benches also builds tests target for the crate

[GuillaumeLagrange]

Problem

Hello,

When running cargo build --benches, one might expect to only build the bench targets.
This is also the case for cargo bench command.

When building the

Steps

1. Create a hello world crate with some basic tests
2. Add a basic bench
3. Add a compilation error in a test
4. Run cargo build --benches, see compilation error

Possible Solution(s)

I have not deep dived into the cargo code, but bench targets should not build the test target, especially since benches are generally built in a release profile, it kind of makes no sense to build the targets in the release profile as well.

Notes

Sorry if this makes no sense or if it's a duplicate.

If instructions on how to reproduce are not clear enough I can provide a simple repository!

Version

cargo 1.85.0 (d73d2caf9 2024-12-31)
release: 1.85.0
commit-hash: d73d2caf9e41a39daf2a8d6ce60ec80bf354d2a7
commit-date: 2024-12-31
host: x86_64-unknown-linux-gnu
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.9.0-DEV (sys:0.4.74+curl-8.9.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: NixOS 25.5.0 [64-bit]

[ehuss]

Thanks for the report! I believe this is somewhat expected behavior (in some ways similar to #6454). Building benchmarks also sets cfg(test) and that is what #[test] annotated functions use to determine if they are compiled or not. I don't know what @rust-lang/testing-devex thinks, I'm not aware of any intentions to adding a separate cfg just for benchmarks (and would be difficult to removing cfg(test) without an edition).