error[E0277]: expected a `FnOnce()` closure, found `()`
  --> $DIR/issue-63279.rs:6:11
   |
LL | fn c() -> Closure {
   |           ^^^^^^^ expected an `FnOnce()` closure, found `()`
   |
   = help: the trait `FnOnce()` is not implemented for `()`
   = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`

error[E0277]: expected a `FnOnce()` closure, found `()`
  --> $DIR/issue-63279.rs:8:11
   |
LL |     || -> Closure { || () }
   |           ^^^^^^^ expected an `FnOnce()` closure, found `()`
   |
   = help: the trait `FnOnce()` is not implemented for `()`
   = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`

error[E0308]: mismatched types
  --> $DIR/issue-63279.rs:8:21
   |
LL |     || -> Closure { || () }
   |                     ^^^^^ expected `()`, found closure
   |
   = note: expected unit type `()`
                found closure `{closure@$DIR/issue-63279.rs:8:21: 8:23}`
help: use parentheses to call this closure
   |
LL |     || -> Closure { (|| ())() }
   |                     +     +++

error[E0308]: mismatched types
  --> $DIR/issue-63279.rs:8:5
   |
LL |     || -> Closure { || () }
   |     ^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found closure
   |
   = note: expected unit type `()`
                found closure `{closure@$DIR/issue-63279.rs:8:5: 8:18}`
help: use parentheses to call this closure
   |
LL |     (|| -> Closure { || () })()
   |     +                       +++

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.