Fixed bug #55421 - Protocol::end_statement(): Assertion `0' on

multi-table UPDATE IGNORE.
The problem was that if there was an active SELECT statement
during trigger execution, an error risen during the execution
may cause a crash. The fix is to temporary reset LEX::current_select
before trigger execution and restore it afterwards. This way
errors risen during the trigger execution are processed as
if there was no active SELECT.

mysql-test/r/trigger_notembedded.result:
  added test case result for bug #55421.
mysql-test/t/trigger_notembedded.test:
  added test case for bug #55421.
sql/sql_trigger.cc:
  Reset thd->lex->current_select before start trigger execution
  and restore its original value after execution is finished.
  This is neccessery in order to set error status in 
  diagnostic_area in case of trigger execution failure.

1 files changed, 21 insertions, 0 deletions

diff --git a/mysql-test/r/trigger_notembedded.result b/mysql-test/r/trigger_notembedded.result
index d66308a9bd7..cba41660ced 100644
--- a/mysql-test/r/trigger_notembedded.result
+++ b/mysql-test/r/trigger_notembedded.result
@@ -474,4 +474,25 @@ SHOW CREATE TRIGGER db1.trg;
 ERROR 42000: Access denied; you need the TRIGGER privilege for this operation
 DROP USER 'no_rights'@'localhost';
 DROP DATABASE db1;
+DROP DATABASE IF EXISTS mysqltest_db1;
+CREATE DATABASE mysqltest_db1;
+USE mysqltest_db1;
+GRANT ALL ON mysqltest_db1.* TO mysqltest_u1@localhost;
+CREATE TABLE t1 (
+a1 int,
+a2 int
+);
+INSERT INTO t1 VALUES (1, 20);
+CREATE TRIGGER mysqltest_db1.upd_t1
+BEFORE UPDATE ON t1 FOR EACH ROW SET new.a2 = 200;
+CREATE TABLE t2 (
+a1 int
+);
+INSERT INTO t2 VALUES (2);
+REVOKE ALL PRIVILEGES, GRANT OPTION FROM mysqltest_u1@localhost;
+UPDATE IGNORE t1, t2 SET t1.a1 = 2, t2.a1 = 3 WHERE t1.a1 = 1 AND t2.a1 = 2;
+ERROR 42000: TRIGGER command denied to user 'mysqltest_u1'@'localhost' for table 't1'
+DROP DATABASE mysqltest_db1;
+DROP USER mysqltest_u1@localhost;
+USE test;
 End of 5.1 tests.