Fixed bug mdev-5611.

The method Item_field::update_table_bitmaps() should not try
to mark the bit for a self-referencing virtual column.

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

@@ -316,4 +316,9 @@ ERROR HY000: The value specified for computed column 'd' in table 't1' ignored
 INSERT INTO `test`.`t1`(`a`,`b`,`c`,`d`) VALUES ( '1','a',NULL,'a');
 ERROR HY000: The value specified for computed column 'd' in table 't1' ignored
 drop table t1;
+#
+# MDEV-5611: self-referencing virtual column
+#
+create table t1 (a int, b int as (b is null) virtual);
+ERROR HY000: A computed column cannot be based on a computed column
 # end of 5.3 tests

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

@@ -275,4 +275,11 @@ UPDATE `test`.`t1` SET `d`='b' WHERE `a`='1' AND `b`='a' AND `c`='1' AND  `d`='a
 INSERT INTO `test`.`t1`(`a`,`b`,`c`,`d`) VALUES ( '1','a',NULL,'a');
 drop table t1;
 
+--echo #
+--echo # MDEV-5611: self-referencing virtual column
+--echo #
+
+--error ER_VCOL_BASED_ON_VCOL
+create table t1 (a int, b int as (b is null) virtual);
+
 --echo # end of 5.3 tests

sql/item.h

@@ -1877,7 +1877,11 @@ class Item_field :public Item_ident
       tab->merge_keys.merge(field->part_of_key);
       if (tab->read_set)
         bitmap_fast_test_and_set(tab->read_set, field->field_index);
-      if (field->vcol_info)
+      /* 
+        Do not mark a self-referecing virtual column.
+        Such virtual columns are reported as invalid.
+      */
+      if (field->vcol_info && tab->vcol_set)
         tab->mark_virtual_col(field);
     }
   }