Re: SQL:2023 JSON simplified accessor support

hi.

I have applied for 0001 to 0006.

static void
jsonb_subscript_transform(SubscriptingRef *sbsref,
List **indirection,
ParseState *pstate,
bool isSlice,
bool isAssignment)
{
List *upperIndexpr = NIL;
ListCell *idx;
sbsref->refrestype = JSONBOID;
sbsref->reftypmod = -1;
if (jsonb_check_jsonpath_needed(*indirection))
{
sbsref->refjsonbpath =
jsonb_subscript_make_jsonpath(pstate, indirection,
&sbsref->refupperindexpr,
&sbsref->reflowerindexpr);
return;
}
foreach(idx, *indirection)
{
Node *i = lfirst(idx);
A_Indices *ai;
Node *subExpr;
Assert(IsA(i, A_Indices));
ai = castNode(A_Indices, i);
if (isSlice)
{
Node *expr = ai->uidx ? ai->uidx : ai->lidx;
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("jsonb subscript does not support slices"),
parser_errposition(pstate, exprLocation(expr))));
}

I am confused by the above error handling:
errmsg("jsonb subscript does not support slices").

we can do
select (jsonb '[1,2,3]')[0:1];
or
SELECT (jb).a[2:3].b FROM test_jsonb_dot_notation;

this is by definition, "slices"?
Anyway, I doubt this error handling will ever be reachable.

jsonb_check_jsonpath_needed checks whether the indirection contains is_slice,
but jsonb_subscript_transform already takes isSlice as an argument.
Maybe we can refactor it somehow.

T_String is a primitive node type with no subnodes.
typedef struct String
{
pg_node_attr(special_read_write)
NodeTag type;
char *sval;
} String;
then in src/backend/nodes/nodeFuncs.c:
if (expr && !IsA(expr, String) && WALK(expr))
return true;
we can change it to
if (WALK(expr))
return true;
but in function expression_tree_walker_impl
we have to change it as

case T_MergeSupportFunc:
case T_String:
/* primitive node types with no expression subnodes */
break;