:
./common/pretty.h:59:11:   required from ‘PrettyOStream<S>& operator<<(PrettyOStream<S>&, const T&) [with S = std::__cxx11::basic_ostringstream<char>; T = Xapian::KeyMaker]’
./common/pretty.h:87:15:   required from ‘PrettyOStream<S>& operator<<(PrettyOStream<S>&, const T*) [with S = std::__cxx11::basic_ostringstream<char>; T = Xapian::KeyMaker]’
api/registry.cc:448:5:   required from here
/usr/include/c++/8/ostream:682:5: error: no type named ‘type’ in ‘struct std::enable_if<false, std::basic_ostream<char>&>’
make[2]: *** [Makefile:3259: api/registry.lo] Error 1