[Bug c++/85093] New: wrong number of template arguments does not trigger error when one argument is variadic

[spambox3 at fangwolg dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85093

            Bug ID: 85093
           Summary: wrong number of template arguments does not trigger
                    error when one argument is variadic
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: spambox3 at fangwolg dot de
  Target Milestone: ---

Created attachment 43769
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43769&action=edit
preprocessed example demonstrating the issue

The attached short example code passes two template arguments into a template
defined with one non-variadic template parameters. Although it should be
illegal code, it does not trigger an error with a recent gcc version. The
second (superfluous) template argument is given by a non-empty variadic
template parameter of another class. 

the commandline
g++ --std=c++11  --save-temps bla.cc

finishes without error with gcc 7.2.0. 

Using gcc 4.9.2 on the other hand aborts with the expected error
bla.cc:4:19: error: wrong number of template arguments (2, should be 1)
   typedef A<V,G...> AB;
                   ^
bla.cc:1:25: error: provided for 'template<class V> class A'
 template<class V> class A {};

clang 5.0.0 also reports an error.

here is the source code:

template<class V> class A {};

template<class V, class... G> class B {
  typedef A<V,G...> AB;
  AB ab;
};

int main() {
  B<int,double> b;  
}