error[E0308]: mismatched types
  --> $DIR/issue-10764.rs:4:15
   |
LL | fn main() { f(bar) }
   |             - ^^^ expected "Rust" fn, found "C" fn
   |             |
   |             arguments to this function are incorrect
   |
   = note: expected fn pointer `fn()`
                 found fn item `extern "C" fn() {bar}`
   = note: when the arguments and return types match, functions can be coerced to function pointers
note: function defined here
  --> $DIR/issue-10764.rs:1:4
   |
LL | fn f(_: extern "Rust" fn()) {}
   |    ^ ---------------------

error: aborting due to previous error

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