error: nonexistent builtin attribute `diagnostic::do_not_recommend` used in `#[doc(attribute = "...")]`
  --> $DIR/doc-attribute-unsupported.rs:5:19
   |
LL | #[doc(attribute = "diagnostic::do_not_recommend")]
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: only existing builtin attributes are allowed in core/std

error: aborting due to 1 previous error