error[E0271]: type mismatch resolving `<Result<Result<(), Result<Result<(), Result<Result<(), Option<{integer}>>, ...>>, ...>>, ...> as Future>::Error == Foo`
   ╭▸ $DIR/E0271.rs:20:5
   │
LL │ ┏     Box::new(
LL │ ┃         Ok::<_, ()>(
LL │ ┃             Err::<(), _>(
LL │ ┃                 Ok::<_, ()>(
   ‡ ┃
LL │ ┃     )
   │ ┗━━━━━┛ type mismatch resolving `<Result<Result<(), Result<Result<(), ...>, ...>>, ...> as Future>::Error == Foo`
   ╰╴
note: expected this to be `Foo`
   ╭▸ $DIR/E0271.rs:10:18
   │
LL │     type Error = E;
   │                  ━
   ╰ note: required for the cast from `Box<Result<Result<(), Result<Result<(), Result<Result<(), Option<{integer}>>, ()>>, ()>>, ()>>` to `Box<(dyn Future<Error = Foo> + 'static)>`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0271`.