[Bug c++/52380] New: [C++11] Number of variadic template arguments wrongly interpreted in class template

[ai.azuma at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52380

             Bug #: 52380
           Summary: [C++11] Number of variadic template arguments wrongly
                    interpreted in class template
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: ai.az...@gmail.com


Created attachment 26752
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26752
Output of -v option and preprocessed file

Here is a reproducer;

///////////////////////////////////////////////
// An enclosing class template is necessary to
// reproduce the bug.
template<typename T>
struct S
{
  template<typename U>
  struct Unary                        // Line 5
  {};

  template<unsigned, typename... Args>
  struct Dispatch                     // Line 9
    : public Unary<Args...>
  {};

  template<typename... Args>
  struct Variadic
    : public Dispatch<sizeof...(Args), Args...>
  {};
};

int main()
{
  S<void>::Variadic<void> z;
}
///////////////////////////////////////////////

GCC 4.7.0 20120218 (experimental) with -std=c++11 complains about the above
code;

main.cpp: In instantiation of 'struct S<void>::Dispatch<1u, void>':
main.cpp:14:10:   required from 'struct S<void>::Variadic<void>'
main.cpp:21:27:   required from here
main.cpp:9:10: error: wrong number of template arguments (2, should be 1)
main.cpp:5:10: error: provided for 'template<class T> template<class U> struct
S<T>::Unary'

Obviously, just one template argument is passed to `Unary'. However, GCC
misinterprets the number of template arguments as two.