Re: range_agg with multirange inputs

The following review has been posted through the commitfest application:
make installcheck-world: tested, passed
Implements feature: tested, passed
Spec compliant: not tested
Documentation: not tested

This applies (with some fuzz) and passes installcheck-world, but a rebase
is needed, because 3 lines of context aren't enough to get the doc changes
in the right place in the aggregate function table. (I think generating
the patch with 4 lines of context would be enough to keep that from being
a recurring issue.)

One thing that seems a bit funny is this message in the new
multirange_agg_transfn:

+ if (!type_is_multirange(mltrngtypoid))
+ ereport(ERROR,
+ (errcode(ERRCODE_DATATYPE_MISMATCH),
+ errmsg("range_agg must be called with a multirange")));

It's clearly copied from the corresponding test and message in
range_agg_transfn. They both say "range_agg must be called ...", which
makes perfect sense, as from the user's perspective both messages come
from (different overloads of) a function named range_agg.

Still, it could be odd to have (again from the user's perspective)
a function named range_agg that sometimes says "range_agg must be
called with a range" and other times says "range_agg must be called
with a multirange".

I'm not sure how to tweak the wording (of either message or both) to
make that less weird, but there's probably a way.

I kind of wonder whether either message is really reachable, at least
through the aggregate machinery in the expected way. Won't that machinery
ensure that it is calling the right transfn with the right type of
argument? If that's the case, maybe the messages could only be seen
by someone calling the transfn directly ... which also seems ruled out
for these transfns because the state type is internal. Is this whole test
more of the nature of an assertion?

Regards,
-Chap

The new status of this patch is: Waiting on Author