error[E0308]: mismatched types
  --> $DIR/issue-68648-2.rs:14:17
   |
LL | fn bug<'a, T: Fun<F<'a> = T>>(t: T) -> T::F<'a> {
   |            - this type parameter
LL |     T::identity(())
   |                 ^^ expected type parameter `T`, found `()`
   |
   = note: expected type parameter `T`
                   found unit type `()`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.