cfg!(unsafe(foo)) and --check-cfg=unsafe(cfg(foo)) are erroneously accepted on beta

[Urgau]

cfg!(unsafe(foo)) and --check-cfg=unsafe(cfg(foo)) both are erroneously accepted on beta.

They should not be accepted, neither of them is in any way "unsafe".

Code

I tried this code:

fn main() {
    let _a = cfg!(unsafe(foo));
}

I expected to see this happen: an error saying that unsafe cannot be put here like for #[cfg]&#[cfg_attr].

Instead, this happened: the unsafe is silently accepted.

Version it worked on

It most recently worked on: 1.81

Version with regression

rustc --version --verbose:

rustc 1.82.0-beta.5 (6a3b69c6b 2024-09-27)
binary: rustc
commit-hash: 6a3b69c6b0529151da5fb4568961519a80adccf9
commit-date: 2024-09-27
host: x86_64-unknown-linux-gnu
release: 1.82.0-beta.5
LLVM version: 19.1.0

@rustbot modify labels: +regression-from-stable-to-beta -regression-untriaged

[Noratrieb]

unsafe { 1 } is also accepted, so I feel like it makes sense to accept it

[Urgau]

@Noratrieb except that neither #[cfg(unsafe(foo)] nor #[cfg_attr(unsafe(foo), ...)] is accepted.

error: expected identifier, found keyword `unsafe`
 --> src/main.rs:1:7
  |
1 | #[cfg(unsafe(foo))]
  |       ^^^^^^ expected identifier, found keyword
  |
help: escape `unsafe` to use it as an identifier
  |
1 | #[cfg(r#unsafe(foo))]
  |       ++

cfg! is also not on the list of unsafe attributes.

[Noratrieb]

makes sense

[Urgau]

Backported in #131423, closing.