MDEV-8554: Server crashes in base_list_iterator::next_fast ...

THD::>save_prep_leaf_list was set to true by multi-table update
statements with mergeable selects and never reset.

Make every statement reset it at start.

mysql-test/r/view.result

@@ -5427,6 +5427,21 @@ View	Create View	character_set_client	collation_connection
 v2	CREATE ALGORITHM=MERGE DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v2` AS select (`t1`.`b` + 1) AS `c` from `t1`	latin1	latin1_swedish_ci
 drop view v2;
 drop table t1;
+#
+# MDEV-8554: Server crashes in base_list_iterator::next_fast on 1st execution of PS with a multi-table update
+#
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (b INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3),(4);
+CREATE TABLE t3 (c INT) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (5),(6);
+CREATE OR REPLACE ALGORITHM=MERGE VIEW v3 AS SELECT * FROM t3;
+PREPARE stmt FROM 'UPDATE t1, t2 SET a = 1 WHERE a IN ( SELECT 0 FROM t3 )';
+UPDATE t1, t2 SET a = 1 WHERE a IN ( SELECT 0 FROM v3 );
+EXECUTE stmt;
+DROP TABLE t1, t2, t3;
+DROP VIEW v3;
 # -----------------------------------------------------------------
 # -- End of 5.5 tests.
 # -----------------------------------------------------------------

mysql-test/t/view.test

@@ -5380,6 +5380,27 @@ show create view v2;
 drop view v2;
 drop table t1;
 
+--echo #
+--echo # MDEV-8554: Server crashes in base_list_iterator::next_fast on 1st execution of PS with a multi-table update
+--echo #
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1),(2); # Not necessary, the table can be empty
+
+CREATE TABLE t2 (b INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3),(4); # Not necessary, the table can be empty
+
+CREATE TABLE t3 (c INT) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (5),(6); # Not necessary, the table can be empty
+
+CREATE OR REPLACE ALGORITHM=MERGE VIEW v3 AS SELECT * FROM t3;
+
+PREPARE stmt FROM 'UPDATE t1, t2 SET a = 1 WHERE a IN ( SELECT 0 FROM t3 )';
+UPDATE t1, t2 SET a = 1 WHERE a IN ( SELECT 0 FROM v3 );
+EXECUTE stmt;
+
+DROP TABLE t1, t2, t3;
+DROP VIEW v3;
+
 --echo # -----------------------------------------------------------------
 --echo # -- End of 5.5 tests.
 --echo # -----------------------------------------------------------------

sql/sql_parse.cc

@@ -6269,6 +6269,8 @@ void THD::reset_for_next_command()
   thd->reset_current_stmt_binlog_format_row();
   thd->binlog_unsafe_warning_flags= 0;
 
+  thd->save_prep_leaf_list= false;
+
   DBUG_PRINT("debug",
              ("is_current_stmt_binlog_format_row(): %d",
               thd->is_current_stmt_binlog_format_row()));