1// PR c++/67130
2// { dg-do compile { target c++14 } }
3
4namespace std {
5template <typename> struct __success_type;
6template <typename> void declval();
7template <typename> class decay {
8public:
9  typedef int type;
10};
11template <typename...> struct common_type;
12struct A {
13  template <typename, typename _Up>
14  static __success_type<typename decay<decltype(declval<_Up>)>::type> _S_test;
15};
16template <typename _Tp, typename _Up> struct __common_type_impl : A {
17  typedef decltype(_S_test<_Tp, _Up>) type;
18};
19template <typename _Tp, typename _Up>
20struct common_type<_Tp, _Up> : __common_type_impl<_Tp, _Up> {};
21}
22template <typename> struct B { struct _; };
23template <typename T> typename B<T>::_ type;
24template <template <typename...> class> struct C;
25template <template <typename...> class f> C<f> metafunction;
26template <typename T> struct B<T>::_ {};
27namespace detail {
28template <typename> struct _decltype;
29}
30template <template <typename...> class F> struct C {
31  template <typename... T>
32  auto operator()(T...)
33      -> decltype(type<typename F<detail::_decltype<T>...>::type>);
34};
35auto common_type = metafunction<std::common_type>(0, 0);
36