https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90047
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> --- template <int a> struct b { static constexpr int c = a; }; template <typename> struct aa; template <typename...> struct d; template <typename e, typename f, typename g, typename... h> struct d<e, f, g, h...> : aa<e>::i {}; template <typename> struct j; template <typename k, long l> struct j<k[l]> : b<true> {}; struct m { typedef b<0> i; }; template <typename> struct n : m::i {}; template <bool> struct o; template <typename p> struct aa { typedef p i; }; template <bool ab> using ac = typename o<ab>::i; class q { template <typename k, typename> using ad = ac<d<n<k>, int, int>::c>; template <typename k, typename = ad<k, void>> q(k &); }; template <typename r> struct s { s(r) { t; } template <ac<!j<r>::c> *> void t(); }; class I { friend char operator<<(char p1, I p2) { return p1 << p2; } q ag; }; int main() { s<char[10]> a = (char *)""; }