`unused_features` triggers on stable `lint_reasons` despite usage

[BennoLossin]

I tried this code:

#![deny(warnings)]
#![allow(stable_features)]
#![feature(lint_reasons)]

#[allow(unused_variables, reason = "my reason")]
fn main() {
    let x = ();
}

I expected to see this happen: no error emitted

Instead, this happened: Error:

error: feature `lint_reasons` is declared but not used
 --> src/main.rs:3:12
  |
3 | #![feature(lint_reasons)]
  |            ^^^^^^^^^^^^
  |
note: the lint level is defined here
 --> src/main.rs:1:9
  |
1 | #![deny(warnings)]
  |         ^^^^^^^^
  = note: `#[deny(unused_features)]` implied by `#[deny(warnings)]`

Meta

rustc --version --verbose:

rustc 1.96.0-nightly (80282b130 2026-03-06)
binary: rustc
commit-hash: 80282b130679a654eaa22f028a908c51be53d436
commit-date: 2026-03-06
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.0

[mu001999]

What will block removing this feature? This feature is unused in fact, the following will compile:

#![deny(warnings)]

#[allow(unused_variables, reason = "my reason")]
fn main() {
    let x = ();
}

[BennoLossin]

To me that counts as using the feature? It just is stable, so there is no need to enable it.

pin-init needs to support earlier (nightly) versions of Rust where the feature is unstable, so we enable the feature when a nightly compiler is detected. The kernel also has MSRV 1.78 and uses RUSTC_BOOTSTRAP=1 to enable the features there.