error[E0308]: mismatched types
  --> $DIR/issue-20862.rs:12:5
   |
LL | fn foo(x: i32) {
   |                - possibly return type missing here?
LL |     |y| x + y
   |     ^^^^^^^^^ expected (), found closure
   |
   = note: expected type `()`
              found type `[closure@$DIR/issue-20862.rs:12:5: 12:14 x:_]`

error[E0618]: expected function, found `()`
  --> $DIR/issue-20862.rs:17:13
   |
LL |     let x = foo(5)(2);
   |             ^^^^^^^^^ not a function

error: aborting due to 2 previous errors

Some errors occurred: E0308, E0618.
For more information about an error, try `rustc --explain E0308`.