Re: Extract numeric filed in JSONB more effectively

Interestingly, when I relabel both places, like this:

     Oid   targetOid = fexpr->funcresulttype;
     Const *target  = makeConst(
       OIDOID, -1, InvalidOid, sizeof(Oid),
       ObjectIdGetDatum(targetOid), false, true);
     RelabelType *rTarget = makeRelabelType((Expr *)target,
       INTERNALOID, -1, InvalidOid, COERCE_IMPLICIT_CAST);
     fexpr->funcid = new_func_id;
     fexpr->args = opexpr->args;
     fexpr->args = list_insert_nth(fexpr->args, 0, rTarget);
     expr = (Expr *)makeRelabelType((Expr *)fexpr,
       targetOid, -1, InvalidOid, COERCE_IMPLICIT_CAST);
   }
   PG_RETURN_POINTER(expr);

EXPLAIN looks like this:

  Seq Scan on pg_temp.test_jsonb
    Output: jsonb_array_element_type(('23'::oid)::internal, test_json,
0), (test_json -> 0)
    Filter: (test_jsonb.json_type = 'scalarint'::text)

With COERCE_IMPLICIT_CAST both places, the relabeling of the
function result is invisible, but the relabeling of the argument
is visible.