https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80830
--- Comment #1 from David Binderman <dcb314 at hotmail dot com> ---
Reduced code, although it doesn't look like legal C++ to me:
class a;
template < b > void operator<<(a , ;
class { friend operator<<(a , ;
template < int = 3 > class c {
friend operator<<<>(, c ;
c<> d({
