error[E0658]: use of unstable library feature 'derive_const' --> $DIR/derive-const-gate.rs:1:3 | LL | #[derive_const(Default)] | ^^^^^^^^^^^^ | = help: add `#![feature(derive_const)]` to the crate attributes to enable error: aborting due to previous error For more information about this error, try `rustc --explain E0658`.