Problem

Hi, I recently encountered an inconsistent behavior of cargo check when I have a macro which expands to something with unexpected_cfgs.

In short, I have a macro definition that expand to something with #[cfg(feature = "my_feature")]. When my_feature is not declared in Cargo.toml of my crate, I expected unexpected_cfgs to be reported whenever I use this macro.
However, whenever I use this macro in a downstream project (which also doesn't declare my_feature), no warning reported.

I originally thought this was a rust-analyzer problem, but after the discussion in rust-lang/rust-analyzer#18461, it seems this is more relevant to cargo.

I would like to understand if this is the expected behavior, because it feels like a bug to me.

Steps

1. Say I have a library mylib, and mylib/lib.rs has

pub fn my_lib_func() {
    println!("my nice little library")
}

#[macro_export]
macro_rules! my_lib_macro {
    () => {
        #[cfg(feature = "my_feature")]
        $crate::my_lib_func()
    };
}

#[test]
fn my_unit_test() {
    // rust-analyzer warning here
    my_lib_macro!();
}

2. Now running cargo check --tests, I got the expected warning:

  --> mylib/src/lib.rs:8:15
   |
8  |         #[cfg(feature = "my_feature")]
   |               ^^^^^^^^^^^^^^^^^^^^^^ help: remove the condition
...
15 |     my_lib_macro!();
   |     --------------- in this macro invocation
   |
   = note: no expected values for `feature`
   = help: consider adding `my_feature` as a feature in `Cargo.toml`
   = 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
   = note: this warning originates in the macro `my_lib_macro` (in Nightly builds, run with -Z macro-backtrace for more info)

3. However, if I use mylib in other packages, say I have another crate, myapp, that depends on mylib.
   In myapp/main.rs, I have:

use mylib::my_lib_macro;

fn main() {
    my_lib_macro!();
}

4. Running cargo check on myapp reports nothing.

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.82.0 (8f40fc59f 2024-08-21)
release: 1.82.0
commit-hash: 8f40fc59fb0c8df91c97405785197f3c630304ea
commit-date: 2024-08-21
host: x86_64-apple-darwin
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.6.0 (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 14.5.0 [64-bit]