[Bug c++/98939] [C++23] Implement P1787R6 "Declarations and where to find them"

[mpolacek at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98939

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I'm having trouble with "Default template arguments are now complete-class
contexts":

class C {
  template <typename...> struct _List;

  template <unsigned long, typename, bool B = value> struct S; // #1

  template <unsigned long _Sz, typename _Uint, typename... _UInts>
  struct S<_Sz, _List<_Uint, _UInts...>>; // #2

  static constexpr bool value = false;
};

#2 wants to lookup_template_class S, but S can contain a DEFERRED_PARSE, so
that's not going to work.  Perhaps we have to delay finish_template_type until
the end of class somehow...