gcc/testsuite/g++.dg/concepts/pr65854.C

// { dg-options "-std=c++17 -fconcepts" }

// Handle alias templates in type requirements.

template<typename T1, typename T2>
struct BTT { };

template<typename T>
struct BTT<T,T> { using type = int; };

template<typename T1, typename T2>
using Alias1 = typename BTT<T1, T2>::type;

template<typename T1, typename T2>
concept bool C()
{
  return requires() { typename Alias1<T1, T2>; };
}

template<typename T1, typename T2>
  requires C<T1, T2>()
int f();

auto i = f<char, int>(); // { dg-error "cannot call function" }