MDEV-28127 EXCHANGE PARTITION with non-matching vcol expression segfault

mysql_compare_tables() treated all columns non-virtual. Now it
properly checks if the columns are virtual and matches expressions.

mysql-test/suite/vcol/r/partition.result

@@ -101,3 +101,25 @@ partition pn values less than (maxvalue));
 insert into t1 (x, b) values (1, ''), (2, ''), (3, 'a'), (4, 'b');
 update t1 set b= 'bar' where x > 0 order by v limit 2;
 drop table t1;
+#
+# MDEV-28127 EXCHANGE PARTITION with non-matching vcol expression segfault
+#
+set @old_mode= @@sql_mode;
+set sql_mode='';
+create table t1 (a int, key(a)) partition by range (a) (partition p values less than (1));
+create table t (a int generated always as (1) virtual, key(a));
+alter table t1 exchange partition p with table t;
+ERROR HY000: Tables have different definitions
+create or replace table t (a int, key(a));
+alter table t1 exchange partition p with table t;
+create or replace table t1 (a int generated always as (1) virtual, key(a)) partition by range (a) (partition p values less than (1));
+create or replace table t (a int generated always as (1) virtual, key(a));
+alter table t1 exchange partition p with table t;
+create or replace table t (a int generated always as (1) stored, key(a));
+alter table t1 exchange partition p with table t;
+ERROR HY000: Tables have different definitions
+insert into t values (1);
+Warnings:
+Warning	1906	The value specified for generated column 'a' in table 't' has been ignored
+drop tables t1, t;
+set sql_mode= @old_mode;

mysql-test/suite/vcol/t/partition.test

@@ -78,3 +78,24 @@ partition by range columns (x) (
 insert into t1 (x, b) values (1, ''), (2, ''), (3, 'a'), (4, 'b');
 update t1 set b= 'bar' where x > 0 order by v limit 2;
 drop table t1;
+
+--echo #
+--echo # MDEV-28127 EXCHANGE PARTITION with non-matching vcol expression segfault
+--echo #
+set @old_mode= @@sql_mode;
+set sql_mode='';
+create table t1 (a int, key(a)) partition by range (a) (partition p values less than (1));
+create table t (a int generated always as (1) virtual, key(a));
+--error ER_TABLES_DIFFERENT_METADATA
+alter table t1 exchange partition p with table t;
+create or replace table t (a int, key(a));
+alter table t1 exchange partition p with table t;
+create or replace table t1 (a int generated always as (1) virtual, key(a)) partition by range (a) (partition p values less than (1));
+create or replace table t (a int generated always as (1) virtual, key(a));
+alter table t1 exchange partition p with table t;
+create or replace table t (a int generated always as (1) stored, key(a));
+--error ER_TABLES_DIFFERENT_METADATA
+alter table t1 exchange partition p with table t;
+insert into t values (1);
+drop tables t1, t;
+set sql_mode= @old_mode;

sql/sql_table.cc

@@ -7538,6 +7538,14 @@ bool mysql_compare_tables(TABLE *table,
 	(uint) (field->flags & NOT_NULL_FLAG))
       DBUG_RETURN(false);
 
+    if (field->vcol_info)
+    {
+      if (!tmp_new_field->field->vcol_info)
+        DBUG_RETURN(false);
+      if (!field->vcol_info->is_equal(tmp_new_field->field->vcol_info))
+        DBUG_RETURN(false);
+    }
+
     /*
       mysql_prepare_alter_table() clears HA_OPTION_PACK_RECORD bit when
       preparing description of existing table. In ALTER TABLE it is later