MDEV-4829 BEFORE INSERT triggers dont issue 1406 error.

  Turn the 'abort_on_warning' on for assigning value to fields.

mysql-test/r/trigger.result

@@ -2273,3 +2273,18 @@ SET optimizer_switch=@save_optimizer_switch;
 DROP TRIGGER tr;
 DROP TABLE t1, t2;
 End of 5.3 tests.
+SET @@session.sql_mode = 'STRICT_ALL_TABLES,STRICT_TRANS_TABLES';
+CREATE TABLE t1 (c CHAR(1) NOT NULL);
+CREATE TRIGGER t1_bi
+BEFORE INSERT
+ON t1
+FOR EACH ROW
+BEGIN
+SET NEW.c = 'www';
+END;
+|
+SET @@session.sql_mode = default;
+INSERT INTO t1 VALUES ('a');
+ERROR 22001: Data too long for column 'c' at row 1
+DROP TRIGGER t1_bi;
+DROP TABLE t1;

mysql-test/t/trigger.test

@@ -2613,3 +2613,25 @@ DROP TABLE t1, t2;
 
 --echo End of 5.3 tests.
 
+#
+# MDEV-4829 BEFORE INSERT triggers dont issue 1406 error
+#
+
+SET @@session.sql_mode = 'STRICT_ALL_TABLES,STRICT_TRANS_TABLES';
+CREATE TABLE t1 (c CHAR(1) NOT NULL);
+DELIMITER |;
+CREATE TRIGGER t1_bi
+  BEFORE INSERT
+  ON t1
+  FOR EACH ROW
+ BEGIN
+  SET NEW.c = 'www';
+ END;
+|
+DELIMITER ;|
+SET @@session.sql_mode = default;
+--error ER_DATA_TOO_LONG
+INSERT INTO t1 VALUES ('a');
+DROP TRIGGER t1_bi;
+DROP TABLE t1;
+

sql/sp_head.cc

@@ -3229,7 +3229,10 @@ sp_instr_set_trigger_field::execute(THD *thd, uint *nextp)
 int
 sp_instr_set_trigger_field::exec_core(THD *thd, uint *nextp)
 {
+  bool sav_abort_on_warning= thd->abort_on_warning;
+  thd->abort_on_warning= thd->is_strict_mode() && !thd->lex->ignore;
   const int res= (trigger_field->set_value(thd, &value) ? -1 : 0);
+  thd->abort_on_warning= sav_abort_on_warning;
   *nextp = m_ip+1;
   return res;
 }