MDEV-34025 Virtual columns do not check assignment cast validity

It was possible to create virtual columns with incompatible
GENERATED ALWAYS expression data types:

  CREATE TABLE t1 (a INT, b POINT GENERATED ALWAYS AS (a));
  CREATE TABLE t1 (a POINT, b INT GENERATED ALWAYS AS (a));

These data type combinations are not allowed in other cases,
e.g. INSERT, UPDATE, SP variable assignment.

Fix:

Disallowing bad combinations of the column data type and its
GENERATED ALWAYS expression data type.

mysql-test/main/gis.result

@@ -5501,5 +5501,12 @@ DROP TABLE t2,t3,t4,t5,t6,t7,t8,t9;
 DROP VIEW v2,v3,v4,v5,v6,v7,v8,v9;
 DROP TABLE t1;
 #
+# MDEV-34025 Virtual columns do not check assignment cast validity
+#
+CREATE TABLE t1 (a INT, b POINT GENERATED ALWAYS AS (a));
+ERROR HY000: Cannot cast 'int' as 'point' in assignment of `test`.`t1`.`b`
+CREATE TABLE t1 (a POINT, b INT GENERATED ALWAYS AS (a));
+ERROR HY000: Cannot cast 'point' as 'int' in assignment of `test`.`t1`.`b`
+#
 # End of 11.5 tests
 #

mysql-test/main/gis.test

@@ -3499,6 +3499,18 @@ DROP TABLE t2,t3,t4,t5,t6,t7,t8,t9;
 DROP VIEW v2,v3,v4,v5,v6,v7,v8,v9;
 DROP TABLE t1;
 
+
+--echo #
+--echo # MDEV-34025 Virtual columns do not check assignment cast validity
+--echo #
+
+--error ER_ILLEGAL_PARAMETER_DATA_TYPES2_FOR_OPERATION
+CREATE TABLE t1 (a INT, b POINT GENERATED ALWAYS AS (a));
+
+--error ER_ILLEGAL_PARAMETER_DATA_TYPES2_FOR_OPERATION
+CREATE TABLE t1 (a POINT, b INT GENERATED ALWAYS AS (a));
+
+
 --echo #
 --echo # End of 11.5 tests
 --echo #

sql/table.cc

@@ -1237,7 +1237,9 @@ bool parse_vcol_defs(THD *thd, MEM_ROOT *mem_root, TABLE *table,
  Set table->map to non-zero temporarily.
  */
  table->map= 1;
- if (vcol && field_ptr[0]->check_vcol_sql_mode_dependency(thd, mode))
+ if (vcol &&
+ (field_ptr[0]->check_vcol_sql_mode_dependency(thd, mode) ||
+ vcol->expr->check_assignability_to(field_ptr[0], false)))
  {
  DBUG_ASSERT(thd->is_error());
  *error_reported= true;