Re: Allow a prosupport function to be attached to an aggregate

David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> I failed to realise that there was no way to set that for user-defined
> aggregates. Not good. While I do agree that lack of extensibility is
> not aligned with the spirit of the project, my current thoughts are
> that now is a bit late to add this to v19.
> Is delaying this until v20 fine for you?
> Or does anyone else feel this is a must-fix for v19?

That seems quite sad. The entire point of the support-function
mechanism is to allow extensibility, so if an extension cannot use
a support hook we have totally failed at implementing that hook.
(As you yourself remarked in a different context, it's unlikely
we would have implemented SupportRequestSimplifyAggref if the only
possible use-case was COUNT(any).)

So I think it's a must-fix. To put my money where my mouth is,
here's a draft patch. (I could not resist the temptation to
improve compute_common_attribute's existing error message,
which pretty well sucks: it's useless in a context that's not
showing you an accurate error pointer.)

regards, tom lane