Can't allow unsafe_attr_outside_unsafe in Rust 2015-2021

[PatchMixolydic]

I tried this code in Rust 2021 (playground):

#![deny(unsafe_attr_outside_unsafe)]

#[allow(unsafe_attr_outside_unsafe)]
mod generated {
    #[no_mangle]
    fn _generated_foo() {}
}

I expected to see this happen: compiles successfully

Instead, this happened:

error: unsafe attribute used without unsafe
 --> src/lib.rs:5:7
  |
5 |     #[no_mangle]
  |       ^^^^^^^^^ usage of unsafe attribute
  |
  = warning: this is accepted in the current edition (Rust 2021) but is a hard error in Rust 2024!
  = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/unsafe-attributes.html>
note: the lint level is defined here
 --> src/lib.rs:1:9
  |
1 | #![deny(unsafe_attr_outside_unsafe)]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
help: wrap the attribute in `unsafe(...)`
  |
5 |     #[unsafe(no_mangle)]
  |       +++++++         +

Meta

rustc --version --verbose:

rustc 1.85.0 (4d91de4e4 2025-02-17)
binary: rustc
commit-hash: 4d91de4e48198da2e33413efdcd9cd2cc0c46688
commit-date: 2025-02-17
host: x86_64-unknown-linux-gnu
release: 1.85.0
LLVM version: 19.1.7

Reproduces in 1.88.0-nightly (2025-05-01 3350c1eb3fd8fe1bee1e) on the Playground.

[PatchMixolydic]

@rustbot labels +A-lints +D-edition +L-unsafe_attr_outside_unsafe

[bjorn3]

Looks like the lint gets attached to the crate root rather than the item that has the #[no_mangle]:

rust/compiler/rustc_parse/src/validate_attr.rs

Line 188 in 2ad5f86

ast::CRATE_NODE_ID,