MDEV-27408 DESC index on a Mroonga table causes wrong order of result set

disallow descending indexes in mroonga

storage/mroonga/ha_mroonga.cpp

@@ -3844,6 +3844,14 @@ int ha_mroonga::storage_create_validate_index(TABLE *table)
     KEY *key_info = &(table->s->key_info[i]);
     // must be single column key
     int key_parts = KEY_N_KEY_PARTS(key_info);
+    for (int j = 0; j < key_parts; j++) {
+      if (key_info->key_part[j].key_part_flag & HA_REVERSE_SORT) {
+        GRN_LOG(ctx, GRN_LOG_ERROR, "DESC indexes are not supported");
+        error = ER_CANT_CREATE_TABLE;
+        my_message(error, "DESC indexes are not supported", MYF(0));
+        DBUG_RETURN(error);
+      }
+    }
     if (key_parts != 1) {
       continue;
     }

storage/mroonga/mysql-test/mroonga/storage/r/index_desc.result

+#
+# MDEV-27408 DESC index on a Mroonga table causes wrong order of result set
+#
+create table t1 (a int, key(a desc));
+ERROR HY000: DESC indexes are not supported
+show warnings;
+Level	Code	Message
+Error	1005	DESC indexes are not supported
+Warning	1030	Got error 1005 "Unknown error 1005" from storage engine Mroonga

storage/mroonga/mysql-test/mroonga/storage/t/index_desc.test

+--source ../../include/mroonga/have_mroonga.inc
+
+--echo #
+--echo # MDEV-27408 DESC index on a Mroonga table causes wrong order of result set
+--echo #
+
+--error ER_CANT_CREATE_TABLE
+create table t1 (a int, key(a desc));
+show warnings;
+#show create table t1;
+#insert into t1 values (1),(3),(2);
+#select * from t1 order by a;
+#drop table t1;
+
+--source ../../include/mroonga/have_mroonga_deinit.inc