Re: sql/json remaining issue

hi.
https://wiki.postgresql.org/wiki/PostgreSQL_17_Open_Items#Open_Issues
issue: Problems with deparsed SQL/JSON query function

original the bug report link:
https://postgr.es/m/CACJufxEqhqsfrg_p7EMyo5zak3d767iFDL8vz_4%3DZBHpOtrghw@mail.gmail.com

forgive me for putting it in the new email thread.
I made the following change, added several tests on it.

--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -4636,10 +4636,10 @@ transformJsonBehavior(ParseState *pstate,
JsonBehavior *behavior,
{
expr = transformExprRecurse(pstate, behavior->expr);
if (!IsA(expr, Const) && !IsA(expr, FuncExpr) &&
- !IsA(expr, OpExpr))
+ !IsA(expr, OpExpr) && !IsA(expr, CoerceViaIO) && !IsA(expr, CoerceToDomain))
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
- errmsg("can only specify a constant, non-aggregate function, or
operator expression for DEFAULT"),
+ errmsg("can only specify a constant, non-aggregate function, or
operator expression or cast expression for DEFAULT"),
parser_errposition(pstate, exprLocation(expr))));
if (contain_var_clause(expr))
ereport(ERROR,

these two expression node also looks like Const:
CoerceViaIO: "foo1"'::jsonb::text
CoerceToDomain: 'foo'::jsonb_test_domain

we need to deal with these two, otherwise we cannot use domain type in
DEFAULT expression.
also the following should not fail:
SELECT JSON_VALUE(jsonb '{"d1": "foo"}', '$.a2' returning text DEFAULT
'"foo1"'::text::json::text ON ERROR);

we have `if (contain_var_clause(expr))` further check it,
so it should be fine?