MDEV-20808 CAST from INET6 to FLOAT does not produce an error

plugin/type_inet/mysql-test/type_inet/type_inet6.result

@@ -698,6 +698,8 @@ DROP TABLE t1,t2;
 #
 SELECT CAST(CAST('::' AS INET6) AS DOUBLE);
 ERROR HY000: Illegal parameter data type inet6 for operation 'double_typecast'
+SELECT CAST(CAST('::' AS INET6) AS FLOAT);
+ERROR HY000: Illegal parameter data type inet6 for operation 'float_typecast'
 SELECT CAST(CAST('::' AS INET6) AS DECIMAL);
 ERROR HY000: Illegal parameter data type inet6 for operation 'decimal_typecast'
 SELECT CAST(CAST('::' AS INET6) AS SIGNED);
@@ -1621,3 +1623,11 @@ SELECT HEX(CAST(a AS BINARY(16))) FROM t1;
 HEX(CAST(a AS BINARY(16)))
 20010DB8000000000000FF0000428329
 DROP TABLE t1;
+#
+# MDEV-20808 CAST from INET6 to FLOAT does not produce an error
+#
+CREATE TABLE t1 (a INET6);
+INSERT INTO t1 VALUES ('::');
+SELECT CAST(a AS FLOAT) FROM t1;
+ERROR HY000: Illegal parameter data type inet6 for operation 'float_typecast'
+DROP TABLE t1;

plugin/type_inet/mysql-test/type_inet/type_inet6.test

@@ -360,6 +360,9 @@ DROP TABLE t1,t2;
 --error ER_ILLEGAL_PARAMETER_DATA_TYPE_FOR_OPERATION
 SELECT CAST(CAST('::' AS INET6) AS DOUBLE);
 
+--error ER_ILLEGAL_PARAMETER_DATA_TYPE_FOR_OPERATION
+SELECT CAST(CAST('::' AS INET6) AS FLOAT);
+
 --error ER_ILLEGAL_PARAMETER_DATA_TYPE_FOR_OPERATION
 SELECT CAST(CAST('::' AS INET6) AS DECIMAL);
 
@@ -1114,3 +1117,13 @@ INSERT INTO t1 VALUES ('2001:db8::ff00:42:8329');
 SELECT HEX(CAST(a AS BINARY)) FROM t1;
 SELECT HEX(CAST(a AS BINARY(16))) FROM t1;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-20808 CAST from INET6 to FLOAT does not produce an error
+--echo #
+
+CREATE TABLE t1 (a INET6);
+INSERT INTO t1 VALUES ('::');
+--error ER_ILLEGAL_PARAMETER_DATA_TYPE_FOR_OPERATION
+SELECT CAST(a AS FLOAT) FROM t1;
+DROP TABLE t1;

plugin/type_inet/sql_type_inet.h

@@ -923,6 +923,12 @@ class Type_handler_inet6: public Type_handler
     return Item_func_or_sum_illegal_param(item);
   }
   bool
+  Item_float_typecast_fix_length_and_dec(Item_float_typecast *item)
+                                         const override
+  {
+    return Item_func_or_sum_illegal_param(item);
+  }
+  bool
   Item_decimal_typecast_fix_length_and_dec(Item_decimal_typecast *item)
                                            const override
   {