error[E0046]: not all trait items implemented, missing: `call` --> $DIR/location-insensitive-scopes-issue-116657.rs:18:1 | LL | fn call(x: Self) -> Self::Output; | --------------------------------- `call` from trait ... LL | impl Callable for T { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `call` in implementation error: unconstrained opaque type --> $DIR/location-insensitive-scopes-issue-116657.rs:22:19 | LL | type Output = impl PlusOne; | ^^^^^^^^^^^^ | = note: `Output` must be used in combination with a concrete type within the same impl error[E0700]: hidden type for `impl PlusOne` captures lifetime that does not appear in bounds --> $DIR/location-insensitive-scopes-issue-116657.rs:28:5 | LL | fn test<'a>(y: &'a mut i32) -> impl PlusOne { | -- ------------ opaque type defined here | | | hidden type `<&'a mut i32 as Callable>::Output` captures the lifetime `'a` as defined here LL | <&mut i32 as Callable>::call(y) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | help: add a `use<...>` bound to explicitly capture `'a` | LL | fn test<'a>(y: &'a mut i32) -> impl PlusOne + use<'a> { | +++++++++ error: aborting due to 3 previous errors Some errors have detailed explanations: E0046, E0700. For more information about an error, try `rustc --explain E0046`.