error[E0308]: mismatched types
  --> $DIR/output-type-mismatch.rs:5:31
   |
LL | fn main() { let i: isize; i = f(); }
   |                               ^^^ expected isize, found ()
   |
   = note: expected type `isize`
              found type `()`

error: aborting due to previous error

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