error[E0658]: `#[doc(alias)]` is experimental
  --> $DIR/feature-gate-doc_alias.rs:1:1
   |
LL | #[doc(alias = "foo")]
   | ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/50146
   = help: add `#![feature(doc_alias)]` to the crate attributes to enable

error: aborting due to previous error

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