error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
  --> $DIR/issue-66286.rs:8:22
   |
LL | pub extern fn foo(_: Vec(u32)) -> u32 {
   |                      ^^^^^^^^ only `Fn` traits may use parentheses
   |
help: use angle brackets instead
   |
LL | pub extern fn foo(_: Vec<u32>) -> u32 {
   |                         ~   ~

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0214`.