Re: EXPLAIN(VERBOSE) to CTE with SEARCH BREADTH FIRST fails

I wrote:
> I do not think that patch is a proper solution, but we do need to do
> something about this.

I poked into this and decided it's an ancient omission within ruleutils.c.
The reason we've not seen it before is probably that you can't get to the
case through the parser. The SEARCH stuff is generating a query structure
basically equivalent to

regression=# with recursive cte (x,r) as (
select 42 as x, row(i, 2.3) as r from generate_series(1,3) i
union all
select x, row((c.r).f1, 4.5) from cte c
)
select * from cte;
ERROR: record type has not been registered

and as you can see, expandRecordVariable fails to figure out what
the referent of "c.r" is. I think that could be fixed (by looking
into the non-recursive term), but given the lack of field demand,
I'm not feeling that it's urgent.

So the omission is pretty obvious from the misleading comment:
actually, Vars referencing RTE_CTE RTEs can also appear in WorkTableScan
nodes, and we're not doing anything to support that. But we only reach
this code when trying to resolve a field of a Var of RECORD type, which
is a case that it seems like the parser can't produce.

It doesn't look too hard to fix: we just have to find the RecursiveUnion
that goes with the WorkTableScan, and drill down into that, much as we
would do in the CteScan case. See attached draft patch. I'm too tired
to beat on this heavily or add a test case, but I have verified that it
passes check-world and handles the example presented in this thread.

regards, tom lane