Fix error message wording

The originals are ambiguous and a bit out of style.

Reviewed-by: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/202412141243.efesjyyvzxsz@alvherre.pgsql

src/backend/parser/parse_expr.c

@@ -4115,8 +4115,9 @@ transformJsonReturning(ParseState *pstate, JsonOutput *output, const char *fname
 		if (returning->typid != JSONOID && returning->typid != JSONBOID)
 			ereport(ERROR,
 					(errcode(ERRCODE_DATATYPE_MISMATCH),
-					 errmsg("cannot use RETURNING type %s in %s",
+					 errmsg("cannot use type %s in RETURNING clause of %s",
 							format_type_be(returning->typid), fname),
+					 errhint("Try returning json or jsonb."),
 					 parser_errposition(pstate, output->typeName->location)));
 	}
 	else
@@ -4235,7 +4236,7 @@ transformJsonSerializeExpr(ParseState *pstate, JsonSerializeExpr *expr)
 			if (typcategory != TYPCATEGORY_STRING)
 				ereport(ERROR,
 						(errcode(ERRCODE_DATATYPE_MISMATCH),
-						 errmsg("cannot use RETURNING type %s in %s",
+						 errmsg("cannot use type %s in RETURNING clause of %s",
 								format_type_be(returning->typid),
 								"JSON_SERIALIZE()"),
 						 errhint("Try returning a string type or bytea.")));

src/interfaces/ecpg/test/expected/sql-sqljson.stderr

@@ -240,12 +240,12 @@ SQL error: null value without indicator on line 84
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_execute on line 99: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_check_PQresult on line 99: bad response - ERROR:  cannot use RETURNING type jsonb in JSON_SERIALIZE()
+[NO_PID]: ecpg_check_PQresult on line 99: bad response - ERROR:  cannot use type jsonb in RETURNING clause of JSON_SERIALIZE()
 HINT:  Try returning a string type or bytea.
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: raising sqlstate 42804 (sqlcode -400): cannot use RETURNING type jsonb in JSON_SERIALIZE() on line 99
+[NO_PID]: raising sqlstate 42804 (sqlcode -400): cannot use type jsonb in RETURNING clause of JSON_SERIALIZE() on line 99
 [NO_PID]: sqlca: code: -400, state: 42804
-SQL error: cannot use RETURNING type jsonb in JSON_SERIALIZE() on line 99
+SQL error: cannot use type jsonb in RETURNING clause of JSON_SERIALIZE() on line 99
 [NO_PID]: ecpg_execute on line 102: query: with val ( js ) as ( values ( '{ "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] }' ) ) select js is json "IS JSON" , js is not json "IS NOT JSON" , js is json value "IS VALUE" , js is json object "IS OBJECT" , js is json array "IS ARRAY" , js is json scalar "IS SCALAR" , js is json without unique keys "WITHOUT UNIQUE" , js is json with unique keys "WITH UNIQUE" from val; with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_execute on line 102: using PQexec

src/test/regress/expected/sqljson.out

@@ -272,7 +272,7 @@ SELECT pg_typeof(JSON_SERIALIZE(NULL));
 
 -- only string types or bytea allowed
 SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING jsonb);
-ERROR:  cannot use RETURNING type jsonb in JSON_SERIALIZE()
+ERROR:  cannot use type jsonb in RETURNING clause of JSON_SERIALIZE()
 HINT:  Try returning a string type or bytea.
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SERIALIZE('{}');
                      QUERY PLAN