MDEV-20818 ER_CRASHED_ON_USAGE or Assertion `length <= column->length' failed in write_block_record on temporary table

The patch for `MDEV-20795 CAST(inet6 AS BINARY) returns wrong result`
unintentionally changed what Item_char_typecast::type_handler()
returns. This broke UNIONs with the BINARY() function, as the Aria
engine started to get columns of unexpected data types.

Restoring previous behaviour, to return
  Type_handler::string_type_handler(max_length).

The prototype for Item_handed_func::return_type_handler() has changed
from:
  const Type_handler *return_type_handler() const
to:
  const Type_handler *return_type_handler(const Item_handled_func *) const

2 files changed, 62 insertions, 0 deletions

diff --git a/plugin/type_inet/mysql-test/type_inet/type_inet6.result b/plugin/type_inet/mysql-test/type_inet/type_inet6.result
index 9e3601e414b..4cc1ac370a0 100644
--- a/plugin/type_inet/mysql-test/type_inet/type_inet6.result
+++ b/plugin/type_inet/mysql-test/type_inet/type_inet6.result
@@ -1931,3 +1931,40 @@ INSERT INTO t1 (a) VALUES ('::');
 ALTER TABLE t1 MODIFY a DATE;
 ERROR 22007: Incorrect date value: '::' for column `test`.`t1`.`a` at row 1
 DROP TABLE t1;
+#
+# MDEV-20818 ER_CRASHED_ON_USAGE or Assertion `length <= column->length' failed in write_block_record on temporary table
+#
+CREATE TABLE t1 (a INET6);
+SELECT
+CAST(a AS BINARY(0)),
+CAST(a AS BINARY(1)),
+CAST(a AS BINARY(16)),
+CAST(a AS BINARY(255)),
+CAST(a AS BINARY(256)),
+CAST(a AS BINARY(512)),
+CAST(a AS BINARY(513)),
+CAST(a AS BINARY(65532)),
+CAST(a AS BINARY(65533)),
+CAST(a AS BINARY(65534)),
+CAST(a AS BINARY(65535)),
+CAST(a AS BINARY(65536)),
+CAST(a AS BINARY(16777215)),
+CAST(a AS BINARY(16777216))
+FROM t1;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					CAST(a AS BINARY(0))	254	0	0	Y	128	0	63
+def					CAST(a AS BINARY(1))	254	1	0	Y	128	0	63
+def					CAST(a AS BINARY(16))	254	16	0	Y	128	0	63
+def					CAST(a AS BINARY(255))	254	255	0	Y	128	0	63
+def					CAST(a AS BINARY(256))	253	256	0	Y	128	0	63
+def					CAST(a AS BINARY(512))	253	512	0	Y	128	0	63
+def					CAST(a AS BINARY(513))	253	513	0	Y	128	0	63
+def					CAST(a AS BINARY(65532))	253	65532	0	Y	128	0	63
+def					CAST(a AS BINARY(65533))	252	65533	0	Y	128	0	63
+def					CAST(a AS BINARY(65534))	252	65534	0	Y	128	0	63
+def					CAST(a AS BINARY(65535))	252	65535	0	Y	128	0	63
+def					CAST(a AS BINARY(65536))	250	65536	0	Y	128	0	63
+def					CAST(a AS BINARY(16777215))	250	16777215	0	Y	128	0	63
+def					CAST(a AS BINARY(16777216))	251	16777216	0	Y	128	0	63
+CAST(a AS BINARY(0))	CAST(a AS BINARY(1))	CAST(a AS BINARY(16))	CAST(a AS BINARY(255))	CAST(a AS BINARY(256))	CAST(a AS BINARY(512))	CAST(a AS BINARY(513))	CAST(a AS BINARY(65532))	CAST(a AS BINARY(65533))	CAST(a AS BINARY(65534))	CAST(a AS BINARY(65535))	CAST(a AS BINARY(65536))	CAST(a AS BINARY(16777215))	CAST(a AS BINARY(16777216))
+DROP TABLE t1;
diff --git a/plugin/type_inet/mysql-test/type_inet/type_inet6.test b/plugin/type_inet/mysql-test/type_inet/type_inet6.test
index a17f5dd69f7..875aaa0b7e9 100644
--- a/plugin/type_inet/mysql-test/type_inet/type_inet6.test
+++ b/plugin/type_inet/mysql-test/type_inet/type_inet6.test
@@ -1411,3 +1411,28 @@ INSERT INTO t1 (a) VALUES ('::');
 --error ER_TRUNCATED_WRONG_VALUE
 ALTER TABLE t1 MODIFY a DATE;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-20818 ER_CRASHED_ON_USAGE or Assertion `length <= column->length' failed in write_block_record on temporary table
+--echo #
+
+CREATE TABLE t1 (a INET6);
+--enable_metadata
+SELECT
+  CAST(a AS BINARY(0)),
+  CAST(a AS BINARY(1)),
+  CAST(a AS BINARY(16)),
+  CAST(a AS BINARY(255)),
+  CAST(a AS BINARY(256)),
+  CAST(a AS BINARY(512)),
+  CAST(a AS BINARY(513)),
+  CAST(a AS BINARY(65532)),
+  CAST(a AS BINARY(65533)),
+  CAST(a AS BINARY(65534)),
+  CAST(a AS BINARY(65535)),
+  CAST(a AS BINARY(65536)),
+  CAST(a AS BINARY(16777215)),
+  CAST(a AS BINARY(16777216))
+FROM t1;
+--disable_metadata
+DROP TABLE t1;