Cargo bench can't find file where it does exist.

[hkBst]

Valid Cargo.toml that includes:

[[bench]]
name = "benches.rs"
harness = false

cause cargo bench to say:

error: failed to parse manifest at `Cargo.toml`

Caused by:
  can't find `benches.rs` bench at `benches/benches.rs` or `benches/benches.rs/main.rs`. Please specify bench.path if you want to use a non-default path.

But:

$ ls benches/
benches.rs

Fix is to use name = "benches", which would have been obvious if the error has used ".rs.rs", so better would probably have been:

error: failed to parse manifest at `Cargo.toml`

Caused by:
  can't find `benches.rs` bench at `benches/benches.rs.rs` or `benches/benches.rs/main.rs`. Please specify bench.path if you want to use a non-default path.

Tested on: cargo 1.90.0-nightly (84709f0 2025-06-22)

[epage]

The problem is that we set_ext on the file name, rather than appending an extension

cargo/src/cargo/util/toml/targets.rs

Lines 977 to 981 in 7388d86

	let target_path_file = {
	let mut path = target_path.clone();
	path.set_extension("rs");
	path
	};

This ended up mismatching because we don't do a name -> path lookup but instead we enumerate all inferred targets and then match a named target to one of the inferred targets.

Since we do enumerate all inferred targets

cargo/src/cargo/util/toml/targets.rs

Line 1026 in 7388d86

inferred: &[(String, PathBuf)],

we could also do a closest_msg

[hkBst]

path.set_extension("rs");

Does that also mean that filenames with internal dots would get the part after the last dot overwritten by this?

[epage]

Sorry, I forgot to clarify. This is specifically when generating the error message that we call set_ext.

[hkBst]

Yeah, I later realized that if this was also used for the path that is actually tried, then it would have worked! So the problem seems to be the discrepancy between what is tried and what is reported.