warning: unexpected `cfg` condition name: `test`

[smoelius]

Very recently, I started seeing the above warning running cargo +nightly udeps.

To reproduce, create a lib.rs file with the following contents:

#![allow(dead_code)]

#[cfg(test)]
fn foo() {}

Running cargo +nightly udeps, I see the following warning:

warning: unexpected `cfg` condition name: `test`
 --> src/lib.rs:3:7
  |
3 | #[cfg(test)]
  |       ^^^^
  |
  = help: expected names are: `clippy`, `debug_assertions`, `doc`, `docsrs`, `doctest`, `feature`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `target_abi`, `target_arch`, `target_endian`, `target_env`, `target_family`, `target_feature`, `target_has_atomic`, `target_has_atomic_equal_alignment`, `target_has_atomic_load_store`, `target_os`, `target_pointer_width`, `target_thread_local`, `target_vendor`, `ub_checks`, `unix`, and `windows`
  = help: consider using a Cargo feature instead
  = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
           [lints.rust]
           unexpected_cfgs = { level = "warn", check-cfg = ['cfg(test)'] }
  = help: or consider adding `println!("cargo::rustc-check-cfg=cfg(test)");` to the top of the `build.rs`
  = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
  = note: `#[warn(unexpected_cfgs)]` on by default

---

I don't know whether this is helpful, but here are the rustc commands I see used by cargo +nightly check and cargo +nightly udeps (respectively). Note the difference in the --check-cfg options.

path-to-rustc --crate-name a --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=149 --crate-type lib --emit=dep-info,metadata -C embed-bitcode=no -C debuginfo=2 -C split-debuginfo=unpacked --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=3460fd85e03fd244 -C extra-filename=-f8564086733bb9d3 --out-dir .../a/target/debug/deps -C incremental=.../a/target/debug/incremental -L dependency=.../a/target/debug/deps

path-to-rustc --crate-name a --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=149 --crate-type lib --emit=dep-info,metadata -C embed-bitcode=no -C debuginfo=2 -C split-debuginfo=unpacked --check-cfg 'cfg(docsrs)' --check-cfg 'cfg(feature, values())' -C metadata=8797eb2d44e088bf -C extra-filename=-8797eb2d44e088bf --out-dir .../a/target/debug/deps -C incremental=.../a/target/debug/incremental -L dependency=.../a/target/debug/deps -Z binary-dep-depinfo

[smoelius]

This PR's merger appears to be the problem: rust-lang/rust#131729

[est31]

As a workaround, I suppose one can pin the nightly to from before that PR merged (say +nightly-2025-01-01). The corresponding cargo PR seems to be rust-lang/cargo#14963 , but it will be 6 weeks until that arrives on stable.

Until then, I suppose we can just add the flag ourselves, there is infrastructure for that. Alternatively one can request from upstream to have the rustc changes reverted until it arrives in cargo stable.

[est31]

Fixed by 4a3d71a . Thanks for the report. I'll do a release in the coming day(s).

[smoelius]

Fixed by 4a3d71a . Thanks for the report. I'll do a release in the coming day(s).

Thanks, @est31!