Re: json_query conditional wrapper bug

Sorry for missing this report and thanks Andrew for the offlist heads up.

On Wed, Sep 4, 2024 at 7:16 PM Peter Eisentraut <peter@eisentraut.org> wrote:
> On 28.08.24 11:21, Peter Eisentraut wrote:
> > These are ok:
> >
> > select json_query('{"a": 1, "b": 42}'::jsonb, 'lax $.b' without wrapper);
> >   json_query
> > ------------
> >   42
> >
> > select json_query('{"a": 1, "b": 42}'::jsonb, 'lax $.b' with
> > unconditional wrapper);
> >   json_query
> > ------------
> >   [42]
> >
> > But this appears to be wrong:
> >
> > select json_query('{"a": 1, "b": 42}'::jsonb, 'lax $.b' with conditional
> > wrapper);
> >   json_query
> > ------------
> >   [42]
> >
> > This should return an unwrapped 42.
>
> If I make the code change illustrated in the attached patch, then I get
> the correct result here.  And various regression test results change,
> which, to me, all look more correct after this patch.  I don't know what
> the code I removed was supposed to accomplish, but it seems to be wrong
> somehow.  In the current implementation, the WITH CONDITIONAL WRAPPER
> clause doesn't appear to work correctly in any case I could identify.

Agreed that this looks wrong.

I've wondered why the condition was like that but left it as-is,
because I thought at one point that that's needed to ensure that the
returned single scalar SQL/JSON item is valid jsonb.

I've updated your patch to include updated test outputs and a nearby
code comment expanded.  Do you intend to commit it or do you prefer
that I do?

-- 
Thanks, Amit Langote