error[E0658]: box expression syntax is experimental; you can call `Box::new` instead --> $DIR/feature-gate-box_syntax.rs:4:13 | LL | let x = box 3; | ^^^^^ | = note: see issue #49733 for more information = help: add `#![feature(box_syntax)]` to the crate attributes to enable error: aborting due to previous error For more information about this error, try `rustc --explain E0658`.