[Bug c++/104295] New: ICE: tree check: expected template_decl, have error_mark in build_deduction_guide, at cp/pt.cc:29079

[hewillk at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104295

            Bug ID: 104295
           Summary: ICE: tree check: expected template_decl, have
                    error_mark in build_deduction_guide, at cp/pt.cc:29079
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

template<class>
struct B;

template <class R>
struct B<R()> {
  template<class T>
  struct C { C(T); };
};

int main() {
  B<void()>::C{0};
}

https://godbolt.org/z/5rxvbd3oe

Maybe dup of Bug 104294, but since their error message is different I opened
this one.