MDEV-30112 ASAN errors in Item_ident::print / generate_partition_syntax

Like in MDEV-16110 we must release items allocated on thd->mem_root by
reopening the table.

MDEV-16290 relocated MDEV-16110 fix in 10.5 so it works for MDEV-28576
as well. 10.3 without MDEV-16290 now duplicates this fix.

mysql-test/main/partition_alter.result

@@ -211,4 +211,17 @@ Table	Op	Msg_type	Msg_text
 test.t	check	status	OK
 delete from t order by b limit 1;
 drop table t;
+#
+# MDEV-30112 ASAN errors in Item_ident::print / generate_partition_syntax
+#
+create table t (a int) partition by hash(a);
+alter table t change a b int, drop a;
+ERROR 42S22: Unknown column 'a' in 't'
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+ PARTITION BY HASH (`a`)
+drop table t;
 # End of 10.3 tests

mysql-test/main/partition_alter.test

@@ -196,4 +196,14 @@ delete from t order by b limit 1;
 # cleanup
 drop table t;
 
+--echo #
+--echo # MDEV-30112 ASAN errors in Item_ident::print / generate_partition_syntax
+--echo #
+create table t (a int) partition by hash(a);
+--error ER_BAD_FIELD_ERROR
+alter table t change a b int, drop a;
+show create table t;
+# Cleanup
+drop table t;
+
 --echo # End of 10.3 tests

sql/sql_table.cc

@@ -8328,6 +8328,8 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
           } /* if (def->change.str) */
         } /* while (def) */
       } /* if (part_field_list || subpart_field_list) */
+      // Force reopen because new column name is on thd->mem_root
+      table->mark_table_for_reopen();
     } /* if (part_info) */
   }
 #endif