[Bug c++/56958] New: Spurious unused variable warning in empty pack expansion

["lucdanton at free dot fr" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56958

             Bug #: 56958
           Summary: Spurious unused variable warning in empty pack
                    expansion
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: lucdanton@free.fr


Created attachment 29872
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29872
Minimal testcase

Using:

g++-snapshot (Debian 20130330-1) 4.9.0 20130330 (experimental) [trunk revision
197260]

$ cat main.cpp 
template<typename... T>
int foo(T... t)
{
    int spurious = 0;
    return false ? foo(t + spurious...) : 0;
}

int main()
{
    return foo();
}

$ g++-snapshot -Wall -std=c++11 main.cpp 
main.cpp: In instantiation of 'int foo(T ...) [with T = {}]':
main.cpp:10:16:   required from here
main.cpp:4:9: warning: variable 'spurious' set but not used
[-Wunused-but-set-variable]
     int spurious = 0;
         ^

No such warning is produced when passing arguments to foo.