gcc/testsuite/g++.dg/cpp2a/concepts-decltype2.C

// { dg-do compile { target c++20 } }

template <class T> concept C = requires(T t) { t; };

template <class T> using A = decltype((T{}, int{}));

template <class T> concept D = C<A<T>>;

template <class T> void f() requires D<T>;

template <class, class>
void g() { f<int>(); }