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From: jian he <jian.universality@gmail.com>
Date: Fri, 11 Jul 2025 13:53:52 +0800
Message-ID: 
 <CACJufxHAPT6Sh6JW-tU0imFbBkD9kU+2vba-yM44UTLx87ckqQ@mail.gmail.com>
Subject: Re: SQL:2023 JSON simplified accessor support
To: Alexandra Wang <alexandra.wang.oss@gmail.com>
Cc: Nikita Malakhov <hukutoc@gmail.com>,
 Vik Fearing <vik@postgresfriends.org>,
	Mark Dilger <mark.dilger@enterprisedb.com>,
 Matheus Alcantara <matheusssilv97@gmail.com>,
	Peter Eisentraut <peter@eisentraut.org>,
 Andrew Dunstan <andrew@dunslane.net>,
	Nikita Glukhov <glukhov.n.a@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
	"David E. Wheeler" <david@justatheory.com>
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On Thu, Jul 10, 2025 at 9:34=E2=80=AFPM jian he <jian.universality@gmail.co=
m> wrote:
>
> ------------------------------------------
> in jsonb_subscript_make_jsonpath we have
>     foreach(lc, *indirection)
> {
>         if (IsA(accessor, String))
>             ....
>         else if (IsA(accessor, A_Indices))
>         else
>             /*
>              * Unsupported node type for creating jsonpath. Instead of
>              * throwing an ERROR, break here so that we create a jsonpath=
 from
>              * as many indirection elements as we can and let
>              * transformIndirection() fallback to alternative logic to ha=
ndle
>              * the remaining indirection elements.
>              */
>               break;
> }
> the above ELSE branch comments look suspicious to me.
> transformIndirection->transformContainerSubscripts->jsonb_subscript_trans=
form->jsonb_subscript_make_jsonpath
> As you can see, transformIndirection have a long distance from
> jsonb_subscript_make_jsonpath,
> let transformIndirection handle remaining indirection elements seems not =
good.
>
context v12-0001 to v12-0006.
this ELSE branch comments is wrong, because
+ if (jsonb_check_jsonpath_needed(*indirection))
+ {
+ jsonb_subscript_make_jsonpath(pstate, indirection, sbsref);
+ if (sbsref->refjsonbpath)
+ return;
+ }
in jsonb_check_jsonpath_needed we already use Assert to confirm that
list "indirection"
is either String or A_Indices Node.

in transformContainerSubscripts we have
sbsroutines->transform(sbsref, indirection, pstate,
                           isSlice, isAssignment);
    /*
     * Error out, if datatype failed to consume any indirection elements.
     */
    if (list_length(*indirection) =3D=3D indirection_length)
    {
        Node       *ind =3D linitial(*indirection);
        if (noError)
            return NULL;
        if (IsA(ind, String))
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("type %s does not support dot notation",
                            format_type_be(containerType)),
                     parser_errposition(pstate, exprLocation(containerBase)=
)));
        else if (IsA(ind, A_Indices))
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("type %s does not support array subscripting",
                            format_type_be(containerType)),
                     parser_errposition(pstate, exprLocation(containerBase)=
)));
        else
            elog(ERROR, "invalid indirection operation: %d", nodeTag(ind));
    }
sbsroutines->transform currently will call
array_subscript_transform, hstore_subscript_transform, jsonb_subscript_tran=
sform

in jsonb_subscript_transform callee we unconditionally do:
    *indirection =3D list_delete_first_n(*indirection, pathlen);
   *indirection =3D list_delete_first_n(*indirection, list_length(upperInde=
xpr));
in array_subscript_transform, we do
*indirection =3D list_delete_first_n(*indirection, ndim);

That means, if sbsroutines->transform not error out and indirection is
not NIL (which is unlikely)
then sbsroutines->transform will consume some induction elements.
instead of the above verbose ereport(ERROR, error handling, we can use Asse=
rt
    Assert(indirection_length > list_length(*indirection));

for the above comments, i did a refactoring based on v12 (0001 to 0006).

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