Bug#29915479 RUNNING COM_REGISTER_SLAVE WITHOUT COM_BINLOG_DUMP CAN RESULTS IN SERVER EXIT

in fact, in MariaDB it cannot, but it can show spurious slaves
in SHOW SLAVE HOSTS.

slave was registered in COM_REGISTER_SLAVE and un-registered after
COM_BINLOG_DUMP. If there was no COM_BINLOG_DUMP, it would never
unregister.

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

+include/master-slave.inc
+[connection master]
+set @old_dbug=@@global.debug_dbug;
+set global debug_dbug='d,fail_com_register_slave';
+stop slave;
+reset slave;
+include/wait_for_slave_to_stop.inc
+start slave;
+stop slave;
+include/wait_for_slave_to_stop.inc
+set global debug_dbug=@old_dbug;
+kill DUMP_THREAD;
+show slave hosts;
+Server_id	Host	Port	Master_id
+start slave;
+include/rpl_end.inc

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

+source include/have_debug.inc;
+source include/have_binlog_format_mixed.inc;
+source include/master-slave.inc;
+
+connection slave;
+
+set @old_dbug=@@global.debug_dbug;
+set global debug_dbug='d,fail_com_register_slave';
+
+stop slave;
+reset slave;
+source include/wait_for_slave_to_stop.inc;
+start slave;
+stop slave;
+source include/wait_for_slave_to_stop.inc;
+set global debug_dbug=@old_dbug;
+
+connection master;
+
+### why is that needed?
+let $id=`SELECT id from information_schema.processlist where command='Binlog Dump'`;
+if ($id) {
+  replace_result $id DUMP_THREAD;
+  eval kill $id;
+  let $wait_condition= SELECT count(*)=0 from information_schema.processlist where command='Binlog Dump';
+  source include/wait_condition.inc;
+}
+
+show slave hosts;
+
+connection slave;
+start slave;
+source include/rpl_end.inc;

sql/slave.cc

@@ -3179,6 +3179,7 @@ pthread_handler_t handle_slave_io(void *arg)
         goto err;
       goto connected;
     }
+    DBUG_EXECUTE_IF("fail_com_register_slave", goto err;);
   }
 
   DBUG_PRINT("info",("Starting reading binary log from master"));

sql/sql_class.cc

@@ -63,6 +63,7 @@
 #include "sql_parse.h"                          // is_update_query
 #include "sql_callback.h"
 #include "sql_connect.h"
+#include "repl_failsafe.h"
 
 /*
   The following is used to initialise Table_ident with a internal
@@ -1496,6 +1497,7 @@ THD::~THD()
   if (rli_slave)
     rli_slave->cleanup_after_session();
   my_free(semisync_info);
+  unregister_slave(this, true, true);
 #endif
 
   free_root(&main_mem_root, MYF(0));

sql/sql_parse.cc

@@ -1269,7 +1269,6 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
       general_log_print(thd, command, "Log: '%s'  Pos: %lu", name, pos);
       if (nlen < FN_REFLEN)
         mysql_binlog_send(thd, thd->strmake(name, nlen), (my_off_t)pos, flags);
-      unregister_slave(thd,1,1);
       /*  fake COM_QUIT -- if we get here, the thread needs to terminate */
       error = TRUE;
       break;