warning: `doc(primitive)` should never have been stable
  --> $DIR/feature-gate-doc_primitive.rs:2:7
   |
LL | #[doc(primitive = "usize")]
   |       ^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(invalid_doc_attributes)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #82730 <https://github.com/rust-lang/rust/issues/82730>

warning: 1 warning emitted