error[E0308]: mismatched types
  --> $DIR/issue-74282.rs:8:15
   |
LL |   type Closure = impl Fn() -> u64;
   |                  ---------------- the expected opaque type
...
LL |       Anonymous(|| {
   |  _____---------_^
   | |     |
   | |     arguments to this struct are incorrect
LL | |         3
LL | |     })
   | |_____^ expected closure, found a different closure
   |
   = note: expected opaque type `Closure`
                  found closure `[closure@$DIR/issue-74282.rs:8:15: 8:17]`
   = note: no two closures, even if identical, have the same type
   = help: consider boxing your closure and/or using it as a trait object
note: tuple struct defined here
  --> $DIR/issue-74282.rs:4:8
   |
LL | struct Anonymous(Closure);
   |        ^^^^^^^^^

error[E0308]: mismatched types
  --> $DIR/issue-74282.rs:8:5
   |
LL |   fn main() {
   |             - expected `()` because of default return type
LL |       let y = || -> Closure { || 3 };
LL | /     Anonymous(|| {
LL | |         3
LL | |     })
   | |      ^- help: consider using a semicolon here: `;`
   | |______|
   |        expected `()`, found struct `Anonymous`

error: aborting due to 2 previous errors

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