Bug#53933 crash when using uncacheable subquery in the having clause of outer query

The problem is in the Item_func_isnull::update_used_tables() function,
bracket is at the wrong place. Because of that isnull item erroneously
is treated as const item. The fix is to set brackets in the right place.

mysql-test/r/func_isnull.result

@@ -5,3 +5,17 @@ flush tables;
 select * from t1 where isnull(to_days(mydate));
 id	mydate
 drop table t1;
+#
+# Bug#53933 crash when using uncacheable subquery in the having clause of outer query
+#
+CREATE TABLE t1 (f1 INT);
+INSERT INTO t1 VALUES (0),(0);
+SELECT ISNULL((SELECT GET_LOCK('Bug#53933', 0) FROM t1 GROUP BY f1)) AS f2
+FROM t1 GROUP BY f1 HAVING f2 = f2;
+f2
+0
+SELECT RELEASE_LOCK('Bug#53933');
+RELEASE_LOCK('Bug#53933')
+1
+DROP TABLE t1;
+End of 5.0 tests

mysql-test/t/func_isnull.test

@@ -13,3 +13,18 @@ select * from t1 where isnull(to_days(mydate));
 drop table t1;
 
 # End of 4.1 tests
+
+--echo #
+--echo # Bug#53933 crash when using uncacheable subquery in the having clause of outer query
+--echo #
+
+CREATE TABLE t1 (f1 INT);
+INSERT INTO t1 VALUES (0),(0);
+
+SELECT ISNULL((SELECT GET_LOCK('Bug#53933', 0) FROM t1 GROUP BY f1)) AS f2
+FROM t1 GROUP BY f1 HAVING f2 = f2;
+SELECT RELEASE_LOCK('Bug#53933');
+
+DROP TABLE t1;
+
+--echo End of 5.0 tests

sql/item_cmpfunc.h

@@ -1209,8 +1209,8 @@ class Item_func_isnull :public Item_bool_func
     else
     {
       args[0]->update_used_tables();
-      if ((const_item_cache= !(used_tables_cache= args[0]->used_tables())) &&
-          !with_subselect)
+      if ((const_item_cache= !(used_tables_cache= args[0]->used_tables()) &&
+          !with_subselect))
       {
 	/* Remember if the value is always NULL or never NULL */
 	cached_value= (longlong) args[0]->is_null();