IS JSON predicate support for domain base type as JSON/JSONB/BYTEA/TEXT

hi.

src/backend/executor/execExpr.c

        case T_JsonIsPredicate:
            {
                JsonIsPredicate *pred = (JsonIsPredicate *) node;
                ExecInitExprRec((Expr *) pred->expr, state, resv, resnull);
                scratch.opcode = EEOP_IS_JSON;
                scratch.d.is_json.pred = pred;
                ExprEvalPushStep(state, &scratch);
                break;
            }

gram.y:
a_expr IS json_predicate_type_constraint

the above shows the a_expr will be transformed and then evaluated.
The exprType type of a_expr as domain should work just fine.
The attached patch implements this, and it seems to be quite straightforward.
(extensive regress tests added)

CREATE DOMAIN jd1 AS JSON CHECK ((VALUE ->'a')::text <> '3');
CREATE DOMAIN jd2 AS JSONB CHECK ((VALUE ->'a') = '1'::jsonb);
CREATE DOMAIN jd4 AS bytea CHECK (VALUE <> '\x61');
SELECT NULL::jd1 IS JSON;
SELECT NULL::jd2 IS JSON;
SELECT NULL::jd4 IS JSON;

in the master, the above 3 IS JSON would return error,
with the attached patch, it will return NULL.

I checked the discussion links [1], but couldn’t find the reason domains aren’t
supported. I guess at that time, we didn't think about this issue.

[1] https://git.postgresql.org/cgit/postgresql.git/commit/?id=6ee30209a6f161d0a267a33f090c70c579c87c00

--
jian
https://www.enterprisedb.com/