error: #[doc(cfg(...))] is experimental (see issue #43781)
  --> $DIR/feature-gate-doc_cfg.rs:11:1
   |
11 | #[doc(cfg(unix))] //~ ERROR: #[doc(cfg(...))] is experimental
   | ^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(doc_cfg)] to the crate attributes to enable

error: aborting due to previous error