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

On Thu, Feb 25, 2021 at 10:19:43AM -0500, Tom Lane wrote:
> For me, the example I gave fails in a non-debug build.  With the code as
> of HEAD, I get "ERROR: stack depth limit exceeded" or a segfault.  With
> your patch applied, it complains about w6 not having the correct form for
> a recursive CTE.

Yes, same here for the test stressing makeDependencyGraphWalker().

The second test I posted for checkWellFormedRecursionWalker() passes
on HEAD in a non-debug build, and triggers an assertion with debug
builds.  So the second test requires CLOBBER_FREED_MEMORY but not
DEBUG_LIST_MEMORY_USAGE.  That's not as good as the first one, but I
would vote for having this second test than none to stress more the
list handling when looking after invalid self-references in a CTE.
This gives me the attached.

I would rather have both tests in the version committed, but if you
think that this addition is not necessary I won't fight hard either :)
--
Michael