MDEV-21693 ALGORITHM=INSTANT does not work for partitioned tables

- Flag ALTER_STORED_COLUMN_TYPE set while doing varchar extension
for partition table. Basically all partition supports
can_be_converted_by_engine() then it should be set to
ALTER_COLUMN_TYPE_CHANGE_BY_ENGINE.

mysql-test/suite/parts/r/partition_special_innodb.result

@@ -327,3 +327,11 @@ disconnect con3;
 disconnect con2;
 disconnect con1;
 connection default;
+CREATE TABLE t1(
+f1 INT, f2 VARCHAR(10) CHARSET ascii,
+f3 CHAR(150) CHARSET ascii,
+f4 TEXT CHARSET ascii)ENGINE=InnoDB
+PARTITION BY RANGE(f1) (PARTITION p1 VALUES LESS THAN(10),
+PARTITION p2 VALUES LESS THAN (100));
+ALTER TABLE t1 convert to charset ascii collate ascii_bin, ALGORITHM=INSTANT;
+DROP TABLE t1;

mysql-test/suite/parts/t/partition_special_innodb.test

@@ -205,3 +205,13 @@ DROP TABLE t4;
 --disconnect con1
 --connection default
 # End of Test #3
+
+# MDEV-21693 ALGORITHM=INSTANT does not work for partitioned tables
+CREATE TABLE t1(
+	f1 INT, f2 VARCHAR(10) CHARSET ascii,
+	f3 CHAR(150) CHARSET ascii,
+	f4 TEXT CHARSET ascii)ENGINE=InnoDB
+	PARTITION BY RANGE(f1) (PARTITION p1 VALUES LESS THAN(10),
+				PARTITION p2 VALUES LESS THAN (100));
+ALTER TABLE t1 convert to charset ascii collate ascii_bin, ALGORITHM=INSTANT;
+DROP TABLE t1;

sql/ha_partition.cc

 /*
   Copyright (c) 2005, 2019, Oracle and/or its affiliates.
-  Copyright (c) 2009, 2019, MariaDB
+  Copyright (c) 2009, 2020, MariaDB
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -11799,6 +11799,40 @@ void ha_partition::clear_top_table_fields()
   DBUG_VOID_RETURN;
 }
 
+bool
+ha_partition::can_convert_string(const Field_string* field,
+		                 const Column_definition& new_type) const
+{
+  for (uint index= 0; index < m_tot_parts; index++)
+  {
+    if (!m_file[index]->can_convert_string(field, new_type))
+      return false;
+  }
+  return true;
+}
+
+bool
+ha_partition::can_convert_varstring(const Field_varstring* field,
+		                    const Column_definition& new_type) const{
+  for (uint index= 0; index < m_tot_parts; index++)
+  {
+    if (!m_file[index]->can_convert_varstring(field, new_type))
+      return false;
+  }
+  return true;
+}
+
+bool
+ha_partition::can_convert_blob(const Field_blob* field,
+		               const Column_definition& new_type) const
+{
+  for (uint index= 0; index < m_tot_parts; index++)
+  {
+    if (!m_file[index]->can_convert_blob(field, new_type))
+      return false;
+  }
+  return true;
+}
 
 struct st_mysql_storage_engine partition_storage_engine=
 { MYSQL_HANDLERTON_INTERFACE_VERSION };

sql/ha_partition.h

@@ -1640,5 +1640,16 @@ class ha_partition :public handler
 
   friend int cmp_key_rowid_part_id(void *ptr, uchar *ref1, uchar *ref2);
   friend int cmp_key_part_id(void *key_p, uchar *ref1, uchar *ref2);
+  bool can_convert_string(
+      const Field_string* field,
+      const Column_definition& new_field) const override;
+
+  bool can_convert_varstring(
+      const Field_varstring* field,
+      const Column_definition& new_field) const override;
+
+  bool can_convert_blob(
+      const Field_blob* field,
+      const Column_definition& new_field) const override;
 };
 #endif /* HA_PARTITION_INCLUDED */