error[E0658]: unless otherwise specified, attributes with the prefix `rustc_` are reserved for internal compiler diagnostics (see issue #29642) --> $DIR/feature-gate-rustc-attrs.rs:15:3 | LL | #[rustc_foo] | ^^^^^^^^^ | = help: add #![feature(rustc_attrs)] to the crate attributes to enable error: aborting due to previous error For more information about this error, try `rustc --explain E0658`.