cfg diagnostic not applied correctly

[Noratrieb]

I tried this code:
cargo add rsa

fn main() {
    println!("Hello, world!");
    rsa::sha2::Sha256;
}

error[E0433]: failed to resolve: could not find `sha2` in `rsa`
 --> src/main.rs:5:10
  |
5 |     rsa::sha2::Sha256;
  |          ^^^^ could not find `sha2` in `rsa`

the cfg diagnostic is missing, although the code path for find_cfg_stripped seems to be hit.