error[E0658]: #[doc(include = "...")] is experimental (see issue #44732)
  --> $DIR/feature-gate-external_doc.rs:11:1
   |
LL | #[doc(include="asdf.md")] //~ ERROR: #[doc(include = "...")] is experimental
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(external_doc)] to the crate attributes to enable

error: aborting due to previous error

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