Re: Typmod associated with multi-row VALUES constructs

Attached is a patch that fixes this by storing typmod info in the RTE.
This turned out to be straightforward, and I think it's definitely
what we should do in HEAD. I have mixed emotions about whether it's
worth doing anything about it in the back branches.

I chose to redefine the existing coltypes/coltypmods/colcollations
lists for CTE RTEs as also applying to VALUES RTEs. That saves a
little space in the RangeTblEntry nodes and allows sharing code
in a couple of places. It's tempting to consider making that apply
to all RTE types, which would permit collapsing expandRTE() and
get_rte_attribute_type() into a single case. But AFAICS there would
be no benefit elsewhere, so I'm not sure the extra code churn is
justified.

BTW, I noticed that the CTE case of expandRTE() fails to assign the
specified location to the generated Vars, which is clearly a bug
though a very minor one; it would result in failing to display a
parse error location in some cases where we would do so for Vars from
other RTE types. That part might be worth back-patching, not sure.

regards, tom lane