error[E0477]: the type `&mut ()` does not fulfill the required lifetime
  --> $DIR/issue-90014.rs:15:20
   |
LL |     type Fut<'a>
   |     ------------ definition of `Fut` from trait
...
LL |     type Fut<'a> = impl Future<Output = ()>;
   |                    ^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: type must outlive the lifetime `'a` as defined here
  --> $DIR/issue-90014.rs:15:14
   |
LL |     type Fut<'a> = impl Future<Output = ()>;
   |              ^^
help: copy the `where` clause predicates from the trait
   |
LL |     type Fut<'a> = impl Future<Output = ()> where Self: 'a;
   |                                             ++++++++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0477`.