I notice that EmitWarningsOnPlaceholders produces its warning messages
at elog level INFO, which makes it nearly useless for bogus custom
variable settings for a preloaded module: the only place such a module
can warn is in the postmaster log, but INFO is too low to go into the
postmaster log by default.
Perhaps we should use WARNING instead?
(I'm actually kind of wondering what the INFO elog level is good for,
as this is just about the only use and it seems wrong.)
regards, tom lane