MDEV-16212 Memory leak with recursive CTE that uses global ORDER BY

           with recursive subquery

There were two problems:
1. The code did not report that usage of global ORDER BY / LIMIT clauses
was not supported yet.
2. The code just reset fake_select_lex of the the unit specifying
a recursive CTE to NULL and that caused memory leaks in some cases.

mysql-test/r/cte_recursive.result

@@ -3233,3 +3233,13 @@ Parent	Child	Path
 654	987	987,
 321	654	987,654,
 DROP TABLE t1;
+#
+# MDEV-16212: recursive CTE with global ORDER BY
+#
+set statement max_recursive_iterations = 2 for
+WITH RECURSIVE qn AS (
+SELECT 1 FROM dual UNION ALL
+SELECT 1 FROM qn
+ORDER BY (SELECT * FROM qn))
+SELECT count(*) FROM qn;
+ERROR 42000: This version of MariaDB doesn't yet support 'global ORDER_BY/LIMIT in recursive CTE spec'

mysql-test/t/cte_recursive.test

@@ -2246,3 +2246,15 @@ FROM cte
 ORDER BY Path;
 
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-16212: recursive CTE with global ORDER BY
+--echo #
+
+--error ER_NOT_SUPPORTED_YET
+set statement max_recursive_iterations = 2 for
+WITH RECURSIVE qn AS (
+SELECT 1 FROM dual UNION ALL
+SELECT 1 FROM qn
+ORDER BY (SELECT * FROM qn))
+SELECT count(*) FROM qn;

sql/sql_union.cc

@@ -521,7 +521,18 @@ bool st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
         with_element->rec_result=
           new (thd_arg->mem_root) select_union_recursive(thd_arg);
         union_result=  with_element->rec_result;
-        fake_select_lex= NULL;
+        if (fake_select_lex)
+	{
+          if (fake_select_lex->order_list.first ||
+              fake_select_lex->explicit_limit)
+          {
+	    my_error(ER_NOT_SUPPORTED_YET, MYF(0),
+                     "global ORDER_BY/LIMIT in recursive CTE spec");
+	    goto err;
+          }
+          fake_select_lex->cleanup();
+          fake_select_lex= NULL;
+        }
       }
       if (!(tmp_result= union_result))
         goto err; /* purecov: inspected */