Problem was that in ALTER TABLE execution variables were set to 1 even when wsrep_auto_increment_control is OFF. We should set them only when wsrep_auto_increment_control is ON.
mysql_prepare_create_table() does my_qsort(sort_keys) on key info. This sorting is indeterministic: a table is created with one order and inplace alter may overwrite frm with another order. Since inplace alter does nothing about key info for MyISAM/Aria storage engines this results in discrepancy between frm and storage engine key definitions. The fix avoids the sorting of keys when no new keys added by ALTER (and this is ok for MyISAM/Aria since it cannot add new keys inplace). There is a case when implicit primary key may be changed when removing NOT NULL from the part of unique key. In that case we update modified_primary_key which is then used to not skip key sorting. According to is_candidate_key() there is no other cases when primary key may be changed implicitly. Notes: mi_keydef_write()/mi_keyseg_write() are used only in mi_create(). They should be used in ha_inplace_alter_table() as well. Aria corruption detection is unimplemented: maria_check_definition() is never used! MySQL 8.0 has this bug as well as of 8.0.26.
There is a case when implicit primary key may be changed when removing NOT NULL from the part of unique key. In that case we update modified_primary_key which is then used to not skip key sorting. According to is_candidate_key() there is no other cases when primary kay may be changed implicitly.
This is a backport of commit fd9ca2a742abe2e91b2b77e70915dec7bd3cd7e1 (MDEV-23295) and commit 9a156e1a23046ba3e37bdb1e4e1ad887d3f5829b (MDEV-23345) to 10.3. An instant ADD/DROP/reorder column could create a dummy table object with the wrong ROW_FORMAT when innodb_default_row_format was changed between CREATE TABLE and ALTER TABLE. prepare_inplace_alter_table_dict(): If we had promised that ALGORITHM=INPLACE is supported, we must preserve the ROW_FORMAT. The rest of the changes are related to adding Alter_inplace_info::inplace_supported to cache the return value of handler::check_if_supported_inplace_alter().