MDEV-24713 Assertion `dict_table_is_comp(index->table)' failed in row_merge_buf_add()

- During online alter conversion from compact to redundant,
virtual column field length already set during
innobase_get_computed_value(). Skip the char(n) check for
virtual column in row_merge_buf_add()

mysql-test/suite/gcol/r/innodb_virtual_index.result

@@ -286,3 +286,17 @@ Warning	1264	Out of range value for column 'va' at row 1
 ALTER TABLE t1 FORCE;
 ERROR 22003: Out of range value for column 'va' at row 1
 DROP TABLE t1;
+#
+# MDEV-24713 Assertion `dict_table_is_comp(index->table)' failed
+#		in row_merge_buf_add()
+#
+CREATE TABLE t1 (id INT PRIMARY KEY, a CHAR(3),
+b CHAR(8) AS (a) VIRTUAL, KEY(b))
+ROW_FORMAT=REDUNDANT ENGINE=InnoDB
+CHARACTER SET utf8;
+INSERT INTO t1 (id,a) VALUES (1,'foo');
+OPTIMIZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	optimize	note	Table does not support optimize, doing recreate + analyze instead
+test.t1	optimize	status	OK
+DROP TABLE t1;

mysql-test/suite/gcol/t/innodb_virtual_index.test

@@ -302,3 +302,15 @@ INSERT IGNORE INTO t1 (id, a) VALUES (NULL, -1);
 --error ER_WARN_DATA_OUT_OF_RANGE
 ALTER TABLE t1 FORCE;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-24713 Assertion `dict_table_is_comp(index->table)' failed
+--echo #		in row_merge_buf_add()
+--echo #
+CREATE TABLE t1 (id INT PRIMARY KEY, a CHAR(3),
+		 b CHAR(8) AS (a) VIRTUAL, KEY(b))
+		 ROW_FORMAT=REDUNDANT ENGINE=InnoDB
+		 CHARACTER SET utf8;
+INSERT INTO t1 (id,a) VALUES (1,'foo');
+OPTIMIZE TABLE t1;
+DROP TABLE t1;

storage/innobase/row/row0merge.cc

@@ -691,7 +691,10 @@ row_merge_buf_add(
 				continue;
 			}
 
-			if (field->len != UNIV_SQL_NULL
+			/* innobase_get_computed_value() sets the
+			length of the virtual column field. */
+			if (v_col == NULL
+			    && field->len != UNIV_SQL_NULL
 			    && col->mtype == DATA_MYSQL
 			    && col->len != field->len) {
 				if (conv_heap != NULL) {