error[E0107]: enum takes 2 generic arguments but 1 generic argument was supplied --> $DIR/issue-65159.rs:5:20 | LL | async fn copy() -> Result<()> | ^^^^^^ -- supplied 1 generic argument | | | expected 2 generic arguments | help: add missing generic argument | LL | async fn copy() -> Result<(), E> | +++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0107`.