MDEV-31112 vcol circular references lead to stack overflow

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

@@ -569,3 +569,14 @@ drop table t1;
 #
 # End of 10.3 tests
 #
+#
+# MDEV-31112 vcol circular references lead to stack overflow
+#
+create table t (a int, c int as (a));
+alter table t alter column c drop default;
+alter table t modify column a int as (c) stored;
+ERROR 01000: Expression for field `a` is referring to uninitialized field `c`
+drop table t;
+#
+# End of 10.4 tests
+#

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

@@ -536,3 +536,16 @@ drop table t1;
 --echo #
 --echo # End of 10.3 tests
 --echo #
+
+--echo #
+--echo # MDEV-31112 vcol circular references lead to stack overflow
+--echo #
+create table t (a int, c int as (a));
+alter table t alter column c drop default;
+--error ER_EXPRESSION_REFERS_TO_UNINIT_FIELD
+alter table t modify column a int as (c) stored;
+drop table t;
+
+--echo #
+--echo # End of 10.4 tests
+--echo #

sql/item.cc

@@ -908,14 +908,15 @@ bool Item_field::register_field_in_write_map(void *arg)
 
   This is used by fix_vcol_expr() when a table is opened
 
-  We don't have to check fields that are marked as NO_DEFAULT_VALUE
-  as the upper level will ensure that all these will be given a value.
+  We don't have to check non-virtual fields that are marked as
+  NO_DEFAULT_VALUE as the upper level will ensure that all these
+  will be given a value.
 */
 
 bool Item_field::check_field_expression_processor(void *arg)
 {
   Field *org_field= (Field*) arg;
-  if (field->flags & NO_DEFAULT_VALUE_FLAG)
+  if (field->flags & NO_DEFAULT_VALUE_FLAG && !field->vcol_info)
     return 0;
   if ((field->default_value && field->default_value->flags) || field->vcol_info)
   {