[Bug c++/68487] New: [concepts] bad "invalid reference to variadic concept" error

[ryan.burn at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68487

            Bug ID: 68487
           Summary: [concepts] bad "invalid reference to variadic concept"
                    error
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ryan.burn at gmail dot com
  Target Milestone: ---

The below code should compile but it gives the error:

main.cpp:7:15: error: invalid reference to function concept ‘template<class X,
class ... Rest> constexpr bool C()’
     requires C<decltype(xs)...>();
               ^

////////////////////////////////////////////////////////////////
template <class X, class... Rest> concept bool C() {   
  return true;   
}   

template <class... Xs>   
  requires requires(const Xs&... xs) {   
    requires C<decltype(xs)...>();   
  }   
struct A {   
};   

int main() {   
  return 0;   
} 
////////////////////////////////////////////////////////////////