Bug #72033 No warning when setting KEY_BLOCK_SIZE on a MyISAM index, value silently ignored

Description:
With InnoDB I'm getting a warning when using key_block_size=... in a situation where it isn't supported:

  mysql> create table t1 (id int primary key, i int, key(i)) 
           engine=innodb   key_block_size=4;
  Query OK, 0 rows affected, 2 warnings (0.85 sec)

  mysql> show warnings;
  | Warning | 1478 | InnoDB: KEY_BLOCK_SIZE requires innodb_file_format > Antelope. |
  | Warning | 1478 | InnoDB: ignoring 

With MyISAM (or actually any non-InnoDB engine?) there is no such warning:

  mysql> create table t2 (id int primary key, i int, key(i)) engine=myisam key_block_size=4;
  Query OK, 0 rows affected (0.05 sec)

  mysql> create table t3 (id int primary key, i int, key(i)) engine=memory key_block_size=4;
  Query OK, 0 rows affected (0.62 sec)

With engine=memory the table default and per-index values are preserved, but probably not used in any meaningful way.

With engine=MyISAM the per-index value defaults to 1024 (1MB?) instead:

  mysql> show create table t2\G
  *************************** 1. row ***************************
         Table: t2
  Create Table: CREATE TABLE `t2` (
    `id` int(11) NOT NULL,
    `i` int(11) DEFAULT NULL,
    PRIMARY KEY (`id`) KEY_BLOCK_SIZE=1024,
    KEY `i` (`i`) KEY_BLOCK_SIZE=1024
  ) ENGINE=MyISAM DEFAULT CHARSET=latin1 KEY_BLOCK_SIZE=4
  1 row in set (0.00 sec)

And even when trying to explicitly set a different value key_block_size will stay as 1024, without any error or warning:

  mysql> alter table t2 add column j int, add key (j) key_block_size=4;
  Query OK, 0 rows affected (0.05 sec)
  Records: 0  Duplicates: 0  Warnings: 0

  mysql> show create table t2\G
  *************************** 1. row ***************************
         Table: t2
  Create Table: CREATE TABLE `t2` (
    `id` int(11) NOT NULL,
    `i` int(11) DEFAULT NULL,
    `j` int(11) DEFAULT NULL,
    PRIMARY KEY (`id`) KEY_BLOCK_SIZE=1024,
    KEY `i` (`i`) KEY_BLOCK_SIZE=1024,
    KEY `j` (`j`) KEY_BLOCK_SIZE=1024
  ) ENGINE=MyISAM DEFAULT CHARSET=latin1 KEY_BLOCK_SIZE=4 
  1 row in set (0.00 sec)

How to repeat:
See embedded statements and results above

Suggested fix:
Raise "key_block_size ignored" warnings when used with engines that don't actually support it ...

Hello Hartmut,

Thank you for the bug report and test case.
Verified as described.

Thanks,
Umesh