MDEV-28959 Online alter ignores strict table mode

* don't disable warnings when catching up
* do propagate warnings up like copy_data_between_tables() does

mysql-test/main/alter_table_online_debug.result

@@ -582,3 +582,33 @@ set debug_sync= 'reset';
 drop table t1;
 drop table t2;
 drop table t3;
+#
+# MDEV-28959 Online alter ignores strict table mode
+#
+create table t1 (a int);
+insert into t1 values (1),(2),(3);
+set debug_sync= 'now wait_for downgraded';
+connection con2;
+set sql_mode='STRICT_TRANS_TABLES,STRICT_ALL_TABLES';
+set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';
+alter table t1 modify a int not null, algorithm=copy, lock=none;
+connection default;
+insert into t1 values (null),(null);
+set debug_sync= 'now signal goforit';
+connection con2;
+ERROR 01000: Data truncated for column 'a' at row 4
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+select * from t1;
+a
+1
+2
+3
+NULL
+NULL
+connection default;
+drop table t1;
+set debug_sync= reset;

mysql-test/main/alter_table_online_debug.test

@@ -720,3 +720,29 @@ set debug_sync= 'reset';
 drop table t1;
 drop table t2;
 drop table t3;
+
+--echo #
+--echo # MDEV-28959 Online alter ignores strict table mode
+--echo #
+create table t1 (a int);
+insert into t1 values (1),(2),(3);
+--send set debug_sync= 'now wait_for downgraded'
+
+--connection con2
+set sql_mode='STRICT_TRANS_TABLES,STRICT_ALL_TABLES';
+set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';
+--send alter table t1 modify a int not null, algorithm=copy, lock=none
+
+--connection default
+--reap
+insert into t1 values (null),(null);
+set debug_sync= 'now signal goforit';
+
+--connection con2
+--error WARN_DATA_TRUNCATED
+--reap
+show create table t1;
+select * from t1;
+--connection default
+drop table t1;
+set debug_sync= reset;

sql/sql_table.cc

@@ -11566,7 +11566,6 @@ static int online_alter_read_from_binlog(THD *thd, rpl_group_info *rgi,
 
   thd_progress_report(thd, 0, my_b_write_tell(log_file));
 
-  Abort_on_warning_instant_set old_abort_on_warning(thd, 0);
   Has_default_error_handler hdeh;
   thd->push_internal_handler(&hdeh);
   do
@@ -11580,7 +11579,8 @@ static int online_alter_read_from_binlog(THD *thd, rpl_group_info *rgi,
     thd->set_n_backup_active_arena(&event_arena, &backup_arena);
     error= ev->apply_event(rgi);
     thd->restore_active_arena(&event_arena, &backup_arena);
-
+    if (thd->is_error())
+      error= 1;
     event_arena.free_items();
     free_root(&event_mem_root, MYF(MY_KEEP_PREALLOC));
     if (ev != rgi->rli->relay_log.description_event_for_exec)