error[E0277]: `main` has invalid return type `i32` --> $DIR/termination-trait-main-i32.rs:1:14 | LL | fn main() -> i32 { | ^^^ `main` can only return types that implement `Termination` | = help: consider using `()`, or a `Result` error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0277`.