Re: BUG #18657: Using JSON_OBJECTAGG with volatile function leads to segfault

On Sat, Oct 19, 2024 at 2:22 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Amit Langote <amitlangote09(at)gmail(dot)com> writes:
> > Another version which expands the comment of JsonValueExpr a little further.

Thanks for the review.

> I still don't like this approach to eval_const_expressions one bit.
> It's undocumented and it pessimizes as many cases as it optimizes.
> Sure, in the case where we can fold formatted_expr to a constant,
> we avoid processing raw_expr at all --- but if we fail to do that,
> we end by recursively simplifying formatted_expr twice (and raw_expr
> once). That's not a win.

Ah, I hadn't considered that. Good point.

> I think it should look more like
>
> /*
> * If we can fold formatted_expr to a constant, we can elide
> * the JsonValueExpr altogether. Otherwise we must process
> * raw_expr too. But JsonFormat is a flat node and requires
> * no simplification, only copying.
> */
> formatted = eval_const_expressions_mutator((Node *) jve->formatted_expr,
> context);
> if (formatted && IsA(formatted, Const))
> return formatted;
> newnode = makeNode(JsonValueExpr);
> newnode->formatted_expr = formatted;
> newnode->raw_expr = eval_const_expressions_mutator((Node *) jve->raw_expr,
> context);
> newnode->format = copyObject(jve->format);
> return newnode;

I decided to use makeJsonValueExpr() here.

> Also, in primnodes.h, personally I'd write
>
> + Expr *raw_expr; /* user-specified expression */
>
> "raw" is a misnomer here, and even if we're not going to rename the
> field, we're not helping anyone by using that word in the comment.

Good point.

Updated patch attached.

--
Thanks, Amit Langote