MDEV-15970 Crash when doing truncate on locked sequence

Problem was that we used table->s->db_type() for accessing
handlerton of opened file instead of table->file->ht

Other bug fixed:
- Ensure that we set error if reopen_tables() fails
  (This was the cause of assert)

mysql-test/suite/sql_sequence/lock.result

@@ -32,3 +32,8 @@ CREATE SEQUENCE seq2;
 LOCK TABLE seq1 WRITE, seq2 WRITE;
 INSERT INTO seq1 VALUES (1, 1, 100000, 1, 1, 100, 1, 1);
 DROP SEQUENCE seq1, seq2;
+CREATE OR REPLACE SEQUENCE s1 ENGINE=MyISAM;
+LOCK TABLE s1 WRITE;
+TRUNCATE TABLE s1;
+ERROR HY000: Storage engine SEQUENCE of the table `test`.`s1` doesn't have this option
+DROP SEQUENCE s1;

mysql-test/suite/sql_sequence/lock.test

@@ -39,7 +39,6 @@ DROP SEQUENCE s1;
 unlock tables;
 DROP SEQUENCE s1;
 
-
 #
 # MDEV-15106 Unexpected ER_WRONG_INSERT_INTO_SEQUENCE upon INSERT with
 # multiple locks on sequences
@@ -51,3 +50,15 @@ LOCK TABLE seq1 WRITE, seq2 WRITE;
 INSERT INTO seq1 VALUES (1, 1, 100000, 1, 1, 100, 1, 1);
 DROP SEQUENCE seq1, seq2;
 
+#
+# MDEV-15970
+# Assertion `!is_set() || (m_status == DA_OK_BULK && is_bulk_op())' failure and/or
+# ER_KEY_NOT_FOUND upon TRUNCATE sequence under lock
+#
+
+CREATE OR REPLACE SEQUENCE s1 ENGINE=MyISAM;
+LOCK TABLE s1 WRITE;
+--error ER_ILLEGAL_HA
+TRUNCATE TABLE s1;
+# Cleanup
+DROP SEQUENCE s1;

sql/sql_truncate.cc

@@ -302,7 +302,7 @@ bool Sql_cmd_truncate_table::lock_table(THD *thd, TABLE_LIST *table_ref,
                                             table_ref->table_name.str, FALSE)))
       DBUG_RETURN(TRUE);
 
-    *hton_can_recreate= ha_check_storage_engine_flag(table->s->db_type(),
+    *hton_can_recreate= ha_check_storage_engine_flag(table->file->ht,
                                                      HTON_CAN_RECREATE);
     table_ref->mdl_request.ticket= table->mdl_ticket;
   }
@@ -428,7 +428,10 @@ bool Sql_cmd_truncate_table::truncate_table(THD *thd, TABLE_LIST *table_ref)
       error= dd_recreate_table(thd, table_ref->db.str, table_ref->table_name.str);
 
       if (thd->locked_tables_mode && thd->locked_tables_list.reopen_tables(thd, false))
-          thd->locked_tables_list.unlink_all_closed_tables(thd, NULL, 0);
+      {
+        thd->locked_tables_list.unlink_all_closed_tables(thd, NULL, 0);
+        error=1;
+      }
 
       /* No need to binlog a failed truncate-by-recreate. */
       binlog_stmt= !error;