// { dg-do compile { target c++11 } }
template <typename... T> struct A // { dg-message "candidates|A" "" { target c++17_down } }
{
  A(T* p) {  // { dg-error "parameter packs|T" }
   (A<T...>*)(p); 
  }
};

A<int> a(0); // { dg-error "no matching|too many initializers" }