error[E0658]: use of an internal attribute
  --> $DIR/feature-gate-doc_primitive.rs:1:1
   |
LL | #[rustc_doc_primitive = "usize"]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
   = note: the `#[rustc_doc_primitive]` attribute is an internal implementation detail that will never be stable
   = note: the `#[rustc_doc_primitive]` attribute is used by the standard library to provide a way to generate documentation for primitive types

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0658`.