Re: BUG #18536: Using WITH inside WITH RECURSIVE triggers a "shouldn't happen" error

I wrote:
> Hmm, that is probably too strong: it will break some queries we've
> historically accepted. What we need is just to forbid self-references
> within the WITH clause. The code actually does that already, it's
> just doing it too late; so we can fix this with a simple re-ordering
> of the error checks, as attached.

Oh ...

regression=# WITH RECURSIVE x(n) AS (
select 0 union select 1 order by (select n from x)) select * from x;
ERROR: missing recursive reference

We have to move *all* of those subsidiary-clause checks to before
the tests of the UNION proper.

regards, tom lane