Re: BUG #19487: Error while executing SQL query involving XML parsing

вс, 30 авг. 2026 г. в 23:04, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Andrey Rachitskiy <pl0h0yp1(at)gmail(dot)com> writes:
> > I think you're right. Fixed it in v3.
>
> I spent some time looking at this, and felt that what we really
> ought to do is update clauses.c's handling of XmlExpr across the
> board. In particular, contain_mutable_functions really shouldn't
> allow XmlExpr in cases where we know it's not immutable. So more
> or less as attached, where I also spent more effort on the comments.
>
> I agree with handling XmlExpr more consistently. Using the
same xmlexpr_is_immutable check for both constant folding
and contain_mutable_functions looks right, including the estimate path.

LGTM

I've got mixed emotions about back-patching this. It's not really
> a bug fix, because we already disclaim the safety of relying on
> CASE for this purpose, cf [1]. I think it might still be reasonable
> to sneak into v19, but I'm unsure that putting it into 18 is a good
> idea.
>
> regards, tom lane
>
> [1]
> https://www.postgresql.org/docs/current/sql-expressions.html#SYNTAX-EXPRESS-EVAL
>
> On back-patching: I share the hesitation about 18. At the same time,
SQL-language functions with this pattern did work on earlier branches and
broke for some users after the plan-cache change in 18. I would be fine
with putting it into 19 and master. If we back-patch to 18, I would treat
it as a narrow regression fix rather than a semantic promise about CASE.
Either way works for me.

Thank you for your time and for all the work you've put into this.

--
Regards,
Rachitskiy Andrey