error[E0046]: not all trait items implemented, missing: `foo` --> $DIR/missing-feature-flag.rs:12:1 | LL | async fn foo(_: T) -> &'static str; | ----------------------------------- `foo` from trait ... LL | impl MyTrait for MyStruct {} | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `foo` in implementation error[E0520]: `foo` specializes an item from a parent `impl`, but that item is not marked `default` --> $DIR/missing-feature-flag.rs:16:5 | LL | impl MyTrait for MyStruct {} | ------------------------------- parent `impl` is here ... LL | async fn foo(_: i32) -> &'static str {} | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot specialize default item `foo` | = note: to specialize, `foo` in the parent `impl` must be marked `default` error[E0308]: mismatched types --> $DIR/missing-feature-flag.rs:16:42 | LL | async fn foo(_: i32) -> &'static str {} | ^^ expected `&str`, found `()` error: aborting due to 3 previous errors Some errors have detailed explanations: E0046, E0308, E0520. For more information about an error, try `rustc --explain E0046`.