Re: BUG #16801: Invalid memory access on WITH RECURSIVE with nested WITHs

On Wed, Feb 24, 2021 at 07:36:26PM -0500, Tom Lane wrote:
> Here's a patch that I think fixes it correctly, including a test
> case that doesn't work with your patch.

Yes, thanks. While looking at that this morning, I have been able to
get a crash with my previous patch once I used more nesting in those
CTEs and your test is much simpler. I also got a test case able to
break things the same way in checkWellFormedRecursionWalker():
WITH RECURSIVE outermost(x) AS (
SELECT 1
UNION (WITH innermost as (WITH innermost2 AS (SELECT 2) SELECT * FROM innermost2)
SELECT * FROM outermost
UNION SELECT * FROM innermost)
)
SELECT * FROM outermost ORDER BY 1;

Your patch does not have a test for that, but it fixes the list
handling. With more nested levels and some UNIONs, the patch I sent
previously would equally break, though I am not sure we need more than
what I am sending here. What do you think about this extra test?
--
Michael