[Bug c++/69978] New: Invalid sizeof... value for variadic template arguments

[yanikibo at yandex dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69978

            Bug ID: 69978
           Summary: Invalid sizeof... value for variadic template
                    arguments
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yanikibo at yandex dot com
  Target Milestone: ---

#include <cstddef>
#include <cassert>

template < std::size_t N >
struct A {  enum : std::size_t {  value = N  };  };

template < class... TL >
using B = A< sizeof...(TL) >;

template < class T >
struct C {  using type = T;  };

template < class... TL >
using D = typename C< B<TL...> >::type;

template < class T, class U, class... TL >
void foo( T, U, TL... )
{
    assert( (B<T, U, TL...>::value) == (2 + sizeof...(TL)) );
    // failed(g++4.7) passed(g++4.8+)

    assert( (D<T, U, TL...>::value) == (2 + sizeof...(TL)) );
    // failed(g++4.7) passed(g++4.8+)

    assert( (C< B<T, U, TL...> >::type::value) == (2 + sizeof...(TL)) );
    // failed(g++4.7+)
}

int main()
{
    foo(10, 20, 30, 40, 50);
}