Currently formatted code (clang-format 21.1.8):

int main() {
  typename[:^^int:] i = 42;
  typename int i = 42;
}

Expected:

int main() {
  typename [:^^int:] i = 42;
  typename int i = 42;
}

Splicer [: :] is not recognized and no space is added after typename.
It seems reasonable to have the same formatting whether the type is spellt out explicitly or it comes from a splicer.