error[E0271]: type mismatch resolving `<[closure@$DIR/issue-63279.rs:6:5: 6:28] as std::ops::FnOnce<()>>::Output == ()`
  --> $DIR/issue-63279.rs:3:1
   |
LL | type Closure = impl FnOnce();
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected opaque type, found ()
   |
   = note: expected type `Closure`
              found type `()`
   = note: the return type of a function must have a statically known size

error: aborting due to previous error

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