error[E0658]: type ascription is experimental --> $DIR/feature-gate-type_ascription.rs:4:13 | LL | let a = 10: u8; | ^^^^^^ | = note: see issue #23416 for more information = help: add `#![feature(type_ascription)]` to the crate attributes to enable error: aborting due to previous error For more information about this error, try `rustc --explain E0658`.