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: `Vec<u32>`

error: aborting due to previous error

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