error[E0308]: mismatched types --> $DIR/issue-10764.rs:14:15 | LL | fn main() { f(bar) } | ^^^ expected "Rust" fn, found "C" fn | = note: expected type `fn()` found type `extern "C" fn() {bar}` error: aborting due to previous error For more information about this error, try `rustc --explain E0308`.