Bug#21383497: DBUG_ABORT() IN VAL_JSON

Item_func_rollup_const does not override val_json(), and attempts to
call it will end up using Item::val_json(), which always raises an
error.

This patch makes Item_func_rollup_const override val_json() and read
the JSON value from its nested item.

mysql-test/r/json.result

@@ -12740,3 +12740,49 @@ NULL
 SELECT JSON_ARRAY(CASE WHEN 1 THEN NULL ELSE NULL END);
 JSON_ARRAY(CASE WHEN 1 THEN NULL ELSE NULL END)
 [null]
+#
+# Bug#21383497 DBUG_ABORT() IN VAL_JSON
+#
+CREATE TABLE t(a INT PRIMARY KEY);
+INSERT INTO t VALUES (1), (2), (3), (4), (5);
+SELECT 1 FROM t GROUP BY ST_ASGEOJSON(POINT(1, 1)) WITH ROLLUP;
+1
+1
+1
+Warnings:
+Warning	1235	This version of MySQL doesn't yet support 'sorting of non-scalar JSON values'
+SELECT JSON_EXTRACT('{"a":1}', '$.a') AS je, COUNT(DISTINCT a)
+FROM t GROUP BY je WITH ROLLUP;
+je	COUNT(DISTINCT a)
+1	5
+NULL	5
+SELECT JSON_EXTRACT(NULL, '$.a') AS je, COUNT(DISTINCT a)
+FROM t GROUP BY je WITH ROLLUP;
+je	COUNT(DISTINCT a)
+NULL	5
+NULL	5
+SELECT JSON_EXTRACT('{"a":1}', '$.a') AS je, a, COUNT(DISTINCT a)
+FROM t GROUP BY je, a WITH ROLLUP;
+je	a	COUNT(DISTINCT a)
+1	1	1
+1	2	1
+1	3	1
+1	4	1
+1	5	1
+1	NULL	5
+NULL	NULL	5
+SELECT JSON_EXTRACT('{"a":1}', '$.a') AS je, a, COUNT(DISTINCT a)
+FROM t GROUP BY a, je WITH ROLLUP;
+je	a	COUNT(DISTINCT a)
+1	1	1
+NULL	1	1
+1	2	1
+NULL	2	1
+1	3	1
+NULL	3	1
+1	4	1
+NULL	4	1
+1	5	1
+NULL	5	1
+NULL	NULL	5
+DROP TABLE t;

mysql-test/t/json.test

@@ -5721,6 +5721,22 @@ SELECT JSON_SET(CASE WHEN 1 THEN NULL ELSE NULL END, '{}', '{}');
 SELECT JSON_VALID(CASE WHEN 1 THEN NULL ELSE NULL END);
 SELECT JSON_ARRAY(CASE WHEN 1 THEN NULL ELSE NULL END);
 
+--echo #
+--echo # Bug#21383497 DBUG_ABORT() IN VAL_JSON
+--echo #
+CREATE TABLE t(a INT PRIMARY KEY);
+INSERT INTO t VALUES (1), (2), (3), (4), (5);
+SELECT 1 FROM t GROUP BY ST_ASGEOJSON(POINT(1, 1)) WITH ROLLUP;
+SELECT JSON_EXTRACT('{"a":1}', '$.a') AS je, COUNT(DISTINCT a)
+FROM t GROUP BY je WITH ROLLUP;
+SELECT JSON_EXTRACT(NULL, '$.a') AS je, COUNT(DISTINCT a)
+FROM t GROUP BY je WITH ROLLUP;
+SELECT JSON_EXTRACT('{"a":1}', '$.a') AS je, a, COUNT(DISTINCT a)
+FROM t GROUP BY je, a WITH ROLLUP;
+SELECT JSON_EXTRACT('{"a":1}', '$.a') AS je, a, COUNT(DISTINCT a)
+FROM t GROUP BY a, je WITH ROLLUP;
+DROP TABLE t;
+
 # Local Variables:
 # mode: sql
 # sql-product: mysql

sql/item_func.cc

@@ -3880,6 +3880,16 @@ my_decimal *Item_func_rollup_const::val_decimal(my_decimal *dec)
   return res;
 }
 
+
+bool Item_func_rollup_const::val_json(Json_wrapper *result)
+{
+  DBUG_ASSERT(fixed == 1);
+  bool res= args[0]->val_json(result);
+  null_value= args[0]->null_value;
+  return res;
+}
+
+
 longlong Item_func_length::val_int()
 {
   DBUG_ASSERT(fixed == 1);

sql/item_func.h

@@ -1393,6 +1393,7 @@ class Item_func_rollup_const :public Item_func
   longlong val_int();
   String *val_str(String *str);
   my_decimal *val_decimal(my_decimal *dec);
+  bool val_json(Json_wrapper *result);
   bool get_date(MYSQL_TIME *ltime, my_time_flags_t fuzzydate)
   {
     return (null_value= args[0]->get_date(ltime, fuzzydate));