template <class, class> constexpr bool is_same_v = false;
template <class T> constexpr bool is_same_v<T, T> = true;

template <class T> concept C = is_same_v<T, void>;

template <class T> requires C<T> using alias = T;

template <class T> struct S {
    void f() requires C<T> && is_same_v<alias<T>, void> {}
};

int main() { S<int>{}; }

<source>:9:41: error: constraints not satisfied for alias template 'alias' [with T = int]
    void f() requires C<T> && is_same_v<alias<T>, void> {}
                                        ^~~~~~~~
<source>:12:14: note: in instantiation of template class 'S<int>' requested here
int main() { S<int>{}; }
             ^
<source>:6:29: note: because 'int' does not satisfy 'C'
template <class T> requires C<T> using alias = T;
                            ^
<source>:4:32: note: because 'is_same_v<int, void>' evaluated to false
template <class T> concept C = is_same_v<T, void>;
                               ^