src/test/ui/suggestions/call-on-unimplemented-fn-ptr.rs

struct Foo;

trait Bar {}

impl Bar for Foo {}

fn needs_bar<T: Bar>(_: T) {}

fn blah(f: fn() -> Foo) {
    needs_bar(f);
    //~^ ERROR the trait bound `fn() -> Foo: Bar` is not satisfied
    //~| HELP use parentheses to call this function pointer
}

fn main() {}