error[E0277]: `main` has invalid return type `impl Copy` --> $DIR/termination-trait-impl-trait.rs:2:14 | LL | fn main() -> impl Copy { } | ^^^^^^^^^ `main` can only return types that implement `Termination` | = help: consider using `()`, or a `Result` error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.