Only allow returning string types or bytea from json_serialize

These are documented to be the allowed types for the RETURNING clause,
but the restriction was not being enforced, which caused a segfault if
another type was specified. Add some testing for this.

Per report from a.kozhemyakin

Backpatch to release 15.

2 files changed, 15 insertions, 0 deletions

diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index 0883261535d..be27bce9d32 100644
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -302,12 +302,22 @@ SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING bytea);
  \x7b20226122203a2031207d20
 (1 row)
 
+SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING varchar);
+ json_serialize 
+----------------
+ { "a" : 1 } 
+(1 row)
+
 SELECT pg_typeof(JSON_SERIALIZE(NULL));
  pg_typeof 
 -----------
  text
 (1 row)
 
+-- only string types or bytea allowed
+SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING jsonb);
+ERROR:  cannot use RETURNING type jsonb in JSON_SERIALIZE
+HINT:  Try returning a string type or bytea
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SERIALIZE('{}');
                      QUERY PLAN                      
 -----------------------------------------------------
diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index 3db81a7ba86..c2742b40f1d 100644
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -60,8 +60,13 @@ SELECT JSON_SERIALIZE('{ "a" : 1 } ');
 SELECT JSON_SERIALIZE('1');
 SELECT JSON_SERIALIZE('1' FORMAT JSON);
 SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING bytea);
+SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING varchar);
 SELECT pg_typeof(JSON_SERIALIZE(NULL));
 
+-- only string types or bytea allowed
+SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING jsonb);
+
+
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SERIALIZE('{}');
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SERIALIZE('{}' RETURNING bytea);