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

Amit Langote <amitlangote09@gmail.com> writes:
> Another version which expands the comment of JsonValueExpr a little further.

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.

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;

(Untested, probably requires more casts than I wrote.)

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.

            regards, tom lane