https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72104
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Romain Geissler from comment #0) > Is this a gcc bug ? Or is this invalid C++ ? GCC 6, Clang and EDG all reject it for the same reason, so it's probably invalid, and is now rejected due to G++ getting better at identifying invalid friend declarations.
