MDEV-15754 Server crashes in fill_record_n_invoke_before_triggers upon ...

insert into table with TIMESTAMP INVISIBLE

Problem:- The segfault occurs because value is null but since timestamp field
is VISIBLE it expects a value , and it tries to call value->save_in_field(..
Timestamp field should not be visible this is the problem.

Solution:- While we clone field for record0_field we don't honor the field
_visibility , this patch changes that.

mysql-test/main/invisible_field.result

@@ -551,3 +551,8 @@ select * from t1 natural join t2;
 b	c	a	d
 2	3	1	4
 drop table t1, t2;
+CREATE TABLE t1 (c CHAR(3), t TIMESTAMP invisible);
+INSERT INTO t1 (c,t) VALUES ('foo','2000-01-01 00:00:00');
+CREATE TRIGGER tr BEFORE INSERT ON t1 FOR EACH ROW SET @a= 1;
+INSERT INTO t1 SELECT * FROM t1;
+DROP TABLE t1;

mysql-test/main/invisible_field.test

@@ -238,3 +238,11 @@ insert t2 (a,b,d) values (1,2,4), (10, 30, 40);
 select * from t1 join t2 using (a);
 select * from t1 natural join t2;
 drop table t1, t2;
+## Triggers  MDEV-15754
+CREATE TABLE t1 (c CHAR(3), t TIMESTAMP invisible);
+INSERT INTO t1 (c,t) VALUES ('foo','2000-01-01 00:00:00');
+
+CREATE TRIGGER tr BEFORE INSERT ON t1 FOR EACH ROW SET @a= 1;
+INSERT INTO t1 SELECT * FROM t1;
+# Cleanup
+DROP TABLE t1;

sql/sql_trigger.cc

@@ -1240,6 +1240,7 @@ bool Table_triggers_list::prepare_record_accessors(TABLE *table)
           return 1;
 
         f->flags= (*fld)->flags;
+        f->invisible= (*fld)->invisible;
         f->null_ptr= null_ptr;
         f->null_bit= null_bit;
         if (null_bit == 128)