I had replaced the light switch in a bathroom with a GFCI combo
outlet /switch so that a hair dryer can be used. The feed comes from
the vanity light with a 12/3 wire into the switchbox, then continues
out from there with a 12/2 to the other circuits.
Because the feed comes from the vanity light, it cannot be protected
by the GFCI. Right? I don't know if the vanity light has to be
protected so it might not matter.