error[E0277]: `?` couldn't convert the error to `()` --> $DIR/issue-32709.rs:4:11 | LL | fn a() -> Result { | --------------- expected `()` because of this LL | Err(5)?; | ^ the trait `From<{integer}>` is not implemented for `()` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = help: the following other types implement trait `From`: <(T,) as From<[T; 1]>> <(T, T) as From<[T; 2]>> <(T, T, T) as From<[T; 3]>> <(T, T, T, T) as From<[T; 4]>> <(T, T, T, T, T) as From<[T; 5]>> <(T, T, T, T, T, T) as From<[T; 6]>> <(T, T, T, T, T, T, T) as From<[T; 7]>> <(T, T, T, T, T, T, T, T) as From<[T; 8]>> and 4 others = note: required for `Result` to implement `FromResidual>` error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.