MDEV-9868 Altering a partitioned table comment does a full copy

let handler::check_if_supported_inplace_alter()
(that detects frm-only changes) to work for partitioned
tables too.

mysql-test/r/alter_table_online.result

-drop table if exists t1,t2,t3;
 create table t1 (a int not null primary key, b int, c varchar(80), e enum('a','b'));
 insert into t1 (a) values (1),(2),(3);
 alter online table t1 modify b int default 5;
@@ -62,3 +61,6 @@ create table t3 (a int not null primary key, b int, c varchar(80)) engine=merge
 alter online table t3 union=(t1,t2);
 ERROR 0A000: LOCK=NONE/SHARED is not supported for this operation. Try LOCK=EXCLUSIVE.
 drop table t1,t2,t3;
+create table t1 (i int) partition by hash(i) partitions 2;
+alter online table t1 comment 'test';
+drop table t1;

mysql-test/t/alter_table_online.test

@@ -3,9 +3,7 @@
 #
 
 --source include/have_innodb.inc
---disable_warnings
-drop table if exists t1,t2,t3;
---enable_warnings
+--source include/have_partition.inc
 #
 # Test of things that can be done online
 #
@@ -101,3 +99,10 @@ create table t3 (a int not null primary key, b int, c varchar(80)) engine=merge
 --error ER_ALTER_OPERATION_NOT_SUPPORTED
 alter online table t3 union=(t1,t2);
 drop table t1,t2,t3;
+
+#
+# MDEV-9868 Altering a partitioned table comment does a full copy
+#
+create table t1 (i int) partition by hash(i) partitions 2;
+alter online table t1 comment 'test';
+drop table t1;

sql/handler.cc

@@ -4209,6 +4209,7 @@ handler::check_if_supported_inplace_alter(TABLE *altered_table,
     Alter_inplace_info::ALTER_COLUMN_DEFAULT |
     Alter_inplace_info::ALTER_COLUMN_OPTION |
     Alter_inplace_info::CHANGE_CREATE_OPTION |
+    Alter_inplace_info::ALTER_PARTITIONED |
     Alter_inplace_info::ALTER_RENAME;
 
   /* Is there at least one operation that requires copy algorithm? */