error[E0658]: language items are subject to change --> $DIR/feature-gate-lang-items.rs:1:1 | LL | #[lang = "foo"] | ^^^^^^^^^^^^^^^ | = help: add `#![feature(lang_items)]` to the crate attributes to enable error[E0522]: definition of an unknown language item: `foo` --> $DIR/feature-gate-lang-items.rs:1:1 | LL | #[lang = "foo"] | ^^^^^^^^^^^^^^^ definition of unknown language item `foo` error: aborting due to 2 previous errors Some errors have detailed explanations: E0522, E0658. For more information about an error, try `rustc --explain E0522`.