A cleanup for the contributed patch for

MDEV-7816 ALTER with DROP INDEX and ADD INDEX .. COMMENT='comment2' ignores the new comment

mysql-test/r/alter_table.result

@@ -2007,6 +2007,12 @@ INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8);
 INSERT INTO t1 SELECT a.* FROM t1 a, t1 b, t1 c, t1 d, t1 e;
 ALTER TABLE t1 MODIFY i FLOAT;
 DROP TABLE t1;
+#
+# Start of 10.1 tests
+#
+#
+# MDEV-7816 ALTER with DROP INDEX and ADD INDEX .. COMMENT='comment2' ignores the new comment
+#
 CREATE TABLE t1(a INT);
 CREATE INDEX i1 ON t1(a) COMMENT 'comment1';
 ALTER TABLE t1 DROP INDEX i1, ADD INDEX i1(a) COMMENT 'comment2';
@@ -2017,3 +2023,6 @@ t1	CREATE TABLE `t1` (
   KEY `i1` (`a`) COMMENT 'comment2'
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1;
+#
+# Start of 10.1 tests
+#

mysql-test/t/alter_table.test

@@ -1697,11 +1697,19 @@ INSERT INTO t1 SELECT a.* FROM t1 a, t1 b, t1 c, t1 d, t1 e;
 ALTER TABLE t1 MODIFY i FLOAT;
 DROP TABLE t1;
 
-#
-# MDEV-7816 ALTER with DROP INDEX and ADD INDEX .. COMMENT='comment2' ignores the new comment
-#
+--echo #
+--echo # Start of 10.1 tests
+--echo #
+
+--echo #
+--echo # MDEV-7816 ALTER with DROP INDEX and ADD INDEX .. COMMENT='comment2' ignores the new comment
+--echo #
 CREATE TABLE t1(a INT);
 CREATE INDEX i1 ON t1(a) COMMENT 'comment1';
 ALTER TABLE t1 DROP INDEX i1, ADD INDEX i1(a) COMMENT 'comment2';
 SHOW CREATE TABLE t1;
 DROP TABLE t1;
+
+--echo #
+--echo # Start of 10.1 tests
+--echo #

sql/sql_table.cc

@@ -6387,8 +6387,9 @@ static bool fill_alter_inplace_info(THD *thd,
     /* Check that key comment is not changed. */
     if (table_key->comment.length != new_key->comment.length ||
         (table_key->comment.length &&
-         strcmp(table_key->comment.str, new_key->comment.str) != 0))
-        goto index_changed;
+         memcmp(table_key->comment.str, new_key->comment.str,
+                table_key->comment.length) != 0))
+      goto index_changed;
 
     continue;