struct Foo{};

Foo foo1(Foo); // Fine

auto foo2(Foo) { return 3; }; // Fine
auto foo3(Foo) -> int { return 3; }; // Fine

auto foo6(Foo) -> int; // Fine
auto foo4(Foo) -> Foo { return Foo(); }; // Fine
auto foo5(Foo) -> Foo; // Ops, "Foo" in parameter list is highlighted as Function, not Type