MDEV-22579 No error when inserting DEFAULT(non_virtual_column) into a virtual column

The code erroneously allowed both:
INSERT INTO t1 (vcol) VALUES (DEFAULT);
INSERT INTO t1 (vcol) VALUES (DEFAULT(non_virtual_column));

The former is OK, but the latter is not.
Adding a new virtual method in Item:

virtual bool vcol_assignment_allowed_value() const { return false; }

Item_null, Item_param and Item_default_value override it.

Item_default_value overrides it in the way to:
- allow DEFAULT
- disallow DEFAULT(col)

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

@@ -409,5 +409,25 @@ aaa
 Warnings:
 Warning	1918	Encountered illegal value '\xF0\xF1\xF2\xF3\xF4\xF5\xF6\xF7' when converting to DOUBLE
 #
+# MDEV-22579 No error when inserting DEFAULT(non_virtual_column) into a virtual column
+#
+SET sql_mode=STRICT_ALL_TABLES;
+CREATE OR REPLACE TABLE t1 (
+a INT NOT NULL DEFAULT 10,
+b INT AS (a+1) VIRTUAL
+) ENGINE=MyISAM;
+INSERT INTO t1 (b) VALUES (10);
+ERROR HY000: The value specified for computed column 'b' in table 't1' has been ignored
+INSERT INTO t1 (b) VALUES (DEFAULT(a));
+ERROR HY000: The value specified for computed column 'b' in table 't1' has been ignored
+INSERT INTO t1 (b) VALUES (DEFAULT);
+INSERT INTO t1 VALUES (10,10);
+ERROR HY000: The value specified for computed column 'b' in table 't1' has been ignored
+INSERT INTO t1 VALUES (10,DEFAULT(a));
+ERROR HY000: The value specified for computed column 'b' in table 't1' has been ignored
+INSERT INTO t1 VALUES (10, DEFAULT);
+DROP TABLE t1;
+SET sql_mode=DEFAULT;
+#
 # End of 10.1 tests
 #

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

@@ -365,6 +365,36 @@ SELECT COLUMN_GET(@aaa, 'price' AS DECIMAL) aaa;
 SELECT COLUMN_GET(@aaa, 'price' AS INT) aaa;
 SELECT COLUMN_GET(@aaa, 'price' AS DOUBLE) aaa;
 
+
+--echo #
+--echo # MDEV-22579 No error when inserting DEFAULT(non_virtual_column) into a virtual column
+--echo #
+
+SET sql_mode=STRICT_ALL_TABLES;
+CREATE OR REPLACE TABLE t1 (
+ a INT NOT NULL DEFAULT 10,
+ b INT AS (a+1) VIRTUAL
+) ENGINE=MyISAM;
+
+# Testing with a column list
+
+--error ER_WARNING_NON_DEFAULT_VALUE_FOR_VIRTUAL_COLUMN
+INSERT INTO t1 (b) VALUES (10);
+--error ER_WARNING_NON_DEFAULT_VALUE_FOR_VIRTUAL_COLUMN
+INSERT INTO t1 (b) VALUES (DEFAULT(a));
+INSERT INTO t1 (b) VALUES (DEFAULT);
+
+# Testing without a column list
+--error ER_WARNING_NON_DEFAULT_VALUE_FOR_VIRTUAL_COLUMN
+INSERT INTO t1 VALUES (10,10);
+--error ER_WARNING_NON_DEFAULT_VALUE_FOR_VIRTUAL_COLUMN
+INSERT INTO t1 VALUES (10,DEFAULT(a));
+INSERT INTO t1 VALUES (10, DEFAULT);
+
+DROP TABLE t1;
+SET sql_mode=DEFAULT;
+
+
 --echo #
 --echo # End of 10.1 tests
 --echo #

sql/item.h

@@ -1128,6 +1128,13 @@ class Item: public Value_source,
     a constant expression. Used in the optimizer to propagate basic constants.
   */
   virtual bool basic_const_item() const { return 0; }
+  /*
+    Determines if the expression is allowed as
+    a virtual column assignment source:
+      INSERT INTO t1 (vcol) VALUES (10)    -> error
+      INSERT INTO t1 (vcol) VALUES (NULL)  -> ok
+  */
+  virtual bool vcol_assignment_allowed_value() const { return false; }
   /* cloning of constant items (0 if it is not const) */
   virtual Item *clone_item(THD *thd) { return 0; }
   virtual cond_result eq_cmp_result() const { return COND_OK; }
@@ -2626,6 +2633,7 @@ class Item_null :public Item_basic_constant
     collation.set(cs, DERIVATION_IGNORABLE, MY_REPERTOIRE_ASCII);
   }
   enum Type type() const { return NULL_ITEM; }
+  bool vcol_assignment_allowed_value() const { return true; }
   bool eq(const Item *item, bool binary_cmp) const { return null_eq(item); }
   double val_real();
   longlong val_int();
@@ -2699,6 +2707,8 @@ class Item_param :public Item_basic_value,
     DECIMAL_VALUE
   } state;
 
+  bool vcol_assignment_allowed_value() const { return state == NULL_VALUE; }
+
   /*
     A buffer for string and long data values. Historically all allocated
     values returned from val_str() were treated as eligible to
@@ -4837,6 +4847,7 @@ class Item_default_value : public Item_field
                 (const char *)NULL),
      arg(a) {}
   enum Type type() const { return DEFAULT_VALUE_ITEM; }
+  bool vcol_assignment_allowed_value() const { return arg == NULL; }
   bool eq(const Item *item, bool binary_cmp) const;
   bool fix_fields(THD *, Item **);
   virtual void print(String *str, enum_query_type query_type);

sql/sql_base.cc

@@ -8889,8 +8889,7 @@ fill_record(THD *thd, TABLE *table_arg, List<Item> &fields, List<Item> &values,
         rfield->field_index ==  table->next_number_field->field_index)
       table->auto_increment_field_not_null= TRUE;
     if (rfield->vcol_info && 
-        value->type() != Item::DEFAULT_VALUE_ITEM && 
-        value->type() != Item::NULL_ITEM &&
+        !value->vcol_assignment_allowed_value() &&
         table->s->table_category != TABLE_CATEGORY_TEMPORARY)
     {
       push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
@@ -9098,8 +9097,7 @@ fill_record(THD *thd, TABLE *table, Field **ptr, List<Item> &values,
     if (field->field_index == autoinc_index)
       table->auto_increment_field_not_null= TRUE;
     if (field->vcol_info && 
-        value->type() != Item::DEFAULT_VALUE_ITEM && 
-        value->type() != Item::NULL_ITEM &&
+        !value->vcol_assignment_allowed_value() &&
         table->s->table_category != TABLE_CATEGORY_TEMPORARY)
     {
       push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,