MDEV-31768: Alias MASTER_DEMOTE_TO_REPLICA for MASTER_DEMOTE_TO_SLAVE

Per MDEV-20601, REPLICA should be an alias for SLAVE in SQL
statements.

Reviewed By:
============
Kristian Nielsen <knielsen@knielsen-hq.org>
Andrei Elkin <andrei.elkin@mariadb.com>

mysql-test/suite/rpl/r/rpl_change_master_demote.result

@@ -683,6 +683,23 @@ connection master;
 CHANGE MASTER TO master_host='127.0.0.1', master_port=SLAVE_PORT, master_user='root', master_use_gtid=Slave_Pos, master_demote_to_slave=invalid;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'invalid' at line 1
 #
+# MDEV-31768
+# Ensure MASTER_DEMOTE_TO_REPLICA aliases MASTER_DEMOTE_TO_SLAVE
+#
+connection slave;
+RESET MASTER;
+include/reset_slave.inc
+CREATE TABLE t_mdev_31768 (a int);
+CHANGE MASTER TO master_use_gtid=Replica_Pos, master_demote_to_replica=1;
+# Validating alias MASTER_DEMOTE_TO_REPLICA provides intended behavior..
+# ..success
+DROP TABLE t_mdev_31768;
+RESET MASTER;
+include/reset_slave.inc
+# Clear primary binlog state to match replica
+connection master;
+RESET MASTER;
+#
 # Cleanup
 #
 connection master;

mysql-test/suite/rpl/t/rpl_change_master_demote.test

@@ -73,6 +73,9 @@
 #   non-boolean value.
 #
 #
+#  Additionally ensure MASTER_DEMOTE_TO_REPLICA aliases MASTER_DEMOTE_TO_SLAVE
+#
+#
 # References:
 #   MDEV-19801: Change defaults for CHANGE MASTER TO so that GTID-based
 #               replication is used by default if master supports it
@@ -454,6 +457,37 @@ EOF
 --eval CHANGE MASTER TO master_host='127.0.0.1', master_port=$SLAVE_MYPORT, master_user='root', master_use_gtid=Slave_Pos, master_demote_to_slave=invalid
 
 
+--echo #
+--echo # MDEV-31768
+--echo # Ensure MASTER_DEMOTE_TO_REPLICA aliases MASTER_DEMOTE_TO_SLAVE
+--echo #
+--connection slave
+RESET MASTER;
+--source include/reset_slave.inc
+CREATE TABLE t_mdev_31768 (a int);
+--let $gtid_binlog_pos= `SELECT @@GLOBAL.gtid_binlog_pos`
+CHANGE MASTER TO master_use_gtid=Replica_Pos, master_demote_to_replica=1;
+--let $gtid_slave_pos=  `SELECT @@GLOBAL.gtid_slave_pos`
+
+--echo # Validating alias MASTER_DEMOTE_TO_REPLICA provides intended behavior..
+if (`SELECT strcmp("$gtid_binlog_pos","$gtid_slave_pos") != 0`)
+{
+    --echo # ..failed
+    --echo # Binlog pos: $gtid_binlog_pos
+    --echo # Replica pos: $gtid_slave_pos
+    die MASTER_DEMOTE_TO_REPLICA does not alias MASTER_DEMOTE_TO_SLAVE correctly;
+}
+--echo # ..success
+
+DROP TABLE t_mdev_31768;
+RESET MASTER;
+--source include/reset_slave.inc
+
+--echo # Clear primary binlog state to match replica
+--connection master
+RESET MASTER;
+
+
 --echo #
 --echo # Cleanup
 --echo #

sql/lex.h

@@ -385,6 +385,7 @@ SYMBOL symbols[] = {
   { "MASTER_SSL_VERIFY_SERVER_CERT", SYM(MASTER_SSL_VERIFY_SERVER_CERT_SYM)},
   { "MASTER_USER",           SYM(MASTER_USER_SYM)},
   { "MASTER_USE_GTID",  SYM(MASTER_USE_GTID_SYM)},
+  { "MASTER_DEMOTE_TO_REPLICA",  SYM(MASTER_DEMOTE_TO_SLAVE_SYM)},
   { "MASTER_DEMOTE_TO_SLAVE",  SYM(MASTER_DEMOTE_TO_SLAVE_SYM)},
   { "MASTER_HEARTBEAT_PERIOD", SYM(MASTER_HEARTBEAT_PERIOD_SYM)},
   { "MATCH",		SYM(MATCH)},