error: missing `fn` or `struct` for function or struct definition
  --> $DIR/extern-no-fn.rs:2:5
   |
LL | extern "C" {
   |            - while parsing this item list starting here
LL |     f();
   |     ^
...
LL | }
   | - the item list ends here
   |
help: if you meant to call a macro, try
   |
LL |     f!();
   |     ~~

error: aborting due to 1 previous error