[Bug c++/66850] Adding a forward declaration of a template containing a template template parm causes ICE on valid code

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66850

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Related test cases:

template <typename T, template <typename U, U> class> struct Sort;

template <template <typename U, U> class Comparator>
struct Sort<int, Comparator>
{
  template <int I>
  struct less_than
  {
    Comparator<int, I> a;
  };
};


========== 

template <typename C, C> struct integral_constant {};

template <typename T, template <typename U, U> class> struct Sort;  

template <template <typename U, U> class Comparator>  
struct Sort<int, Comparator>
{  
    template <int I> struct less_than:
        integral_constant<bool, Comparator<int, I>::value> {};
};