New nightly feature "rustc-check-cfg" doesn't work as advertised by warning hint (cannot dismiss warning) about rust HOT 4 CLOSED

@Urgau

from rust.

It seems to me that since the file is included in both build.rs and the built program, even if rustc-check-cfg suppressed the warnings about the surplus exe config in the program I might still wind up facing warnings about exe in the build.rs, since the println has not run at the time the build.rs is built. However I don't think this is the problem above, because in that case I would have expected the number of warnings to halve on adding the suppression line, not stay the same.

Your analysis here is correct, I think you just missed this tiny note which is that cargo suppresses identical warnings 🙂

Before uncommenting the cargo:rustc-cfg-check line:

...
warning: `spritetest` (build script) generated 4 warnings
warning: `spritetest` (bin "spritetest") generated 4 warnings (4 duplicates)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 11.66s

After:

...
warning: `spritetest` (build script) generated 4 warnings
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.47s

@Urgau what's the right way to deal with check-cfg warnings originating in build.rs?

from rust.

Adding the check-cfg args directly in the lint config should do it¹².

Cargo.toml:

[lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(exe)'] }

from rust.

Adding the check-cfg args directly in the lint config should do it12.

Cargo.toml:

[lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(exe)'] }

Footnotes

1. Note that this was added very recently, around 2 nightly version ago, be sure to update to the latest nightly. ↩
2. Note that using the check-cfg lint config currently produce a warning on beta, we are working on fixing that. ↩

Thank you, I should have updated to NEWEST nightly before filing. I see that with 2024-05-20 nightly rustc the [lint] IS recommended in a hint, so this hint would have solved my problem if I had upgraded this morning before filing.

The lint works as expected and my problem is resolved (lint removes warnings where println does not).

I have a recommendation. If you are merging build.rs and executable warnings, then in principle you know that my "exe" cfg warnings are coming (in part) from build.rs. Currently, you display two recommendations*, the build.rs print and the [lint]. In the case of a cfg warning originating from a build.rs, the build.rs print! will not help and you know that ahead of time. Therefore for these warnings, I suggest you omit the build.rs print recommendation and show only the [lint] recommendation.

If that is impractical, then you may close this issue.

* with rustc 1.80.0-nightly (b92758a9a 2024-05-20) I get:

warning: unexpected `cfg` condition name: `exe`
 --> src/rkyv_types.rs:6:7
  |
6 | #[cfg(exe)]
  |       ^^^
  |
  = help: expected names are: `clippy`, `debug_assertions`, `doc`, `docsrs`, `doctest`, `feature`, `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`, `test`, `ub_checks`, `unix`, `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(exe)'] }
  = help: or consider adding `println!("cargo::rustc-check-cfg=cfg(exe)");` 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

from rust.