error[E0658]: the `#[do_not_recommend]` attribute is an experimental feature --> $DIR/unstable-feature.rs:4:1 | LL | #[do_not_recommend] | ^^^^^^^^^^^^^^^^^^^ | = note: see issue #51992 for more information = help: add `#![feature(do_not_recommend)]` to the crate attributes to enable error: aborting due to previous error For more information about this error, try `rustc --explain E0658`.