BUG#51426: overflow for auto_increment column causes slave to stop

In BUG#49562 we fixed the case where numeric user var events
would not serialize the flag stating whether the value was signed
or unsigned (unsigned_flag). This fixed the case that the slave
would get an overflow while treating the unsigned values as
signed.
      
In this bug, we find that the unsigned_flag can sometimes change
between the moment that the user value is recorded for binlogging
purposes and the actual binlogging time. Since we take the
unsigned_flag from the runtime variable data, at binlogging time,
and the variable value is comes from the copy taken earlier in
the execution, there may be inconsistency in the
User_var_log_event between the variable value and its
unsigned_flag.
      
We fix this by also copying the unsigned_flag of the
user_var_entry when its value is copied, for binlogging
purposes. Later, at binlogging time, we use the copied
unsigned_flag and not the one in the runtime user_var_entry
instance.

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

@@ -206,3 +206,19 @@ Comparing tables master:test.t1 and slave:test.t1
 TRUNCATE t1;
 ## check: contents of both tables master's and slave's
 DROP TABLE t1;
+stop slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+start slave;
+CREATE TABLE t1 ( c INT, PRIMARY KEY (c)) Engine=MyISAM;
+CREATE TRIGGER tr1 AFTER INSERT ON t1 FOR EACH ROW SET @aux = -1 ;
+SET @aux = 10294947273192243200;
+SET @aux1= @aux;
+INSERT INTO t1 VALUES (@aux) , (@aux1);
+ERROR 23000: Duplicate entry '2147483647' for key 'PRIMARY'
+## assertion: master and slave tables are in sync
+Comparing tables master:test.t1 and slave:test.t1
+DROP TRIGGER tr1;
+DROP TABLE t1;

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

@@ -139,3 +139,36 @@ TRUNCATE t1;
 -- connection master
 DROP TABLE t1;
 -- sync_slave_with_master
+
+#####################################################################
+#
+# BUG#51426
+#
+#####################################################################
+-- source include/master-slave-reset.inc
+-- connection master
+
+CREATE TABLE t1 ( c INT, PRIMARY KEY (c)) Engine=MyISAM;
+
+# offending trigger that would reset the unsigned flag for aux before
+# binlogging of User_var_log_event would take place.
+CREATE TRIGGER tr1 AFTER INSERT ON t1 FOR EACH ROW SET @aux = -1 ;
+
+SET @aux = 10294947273192243200;
+SET @aux1= @aux;
+-- error ER_DUP_ENTRY
+INSERT INTO t1 VALUES (@aux) , (@aux1);
+
+-- sync_slave_with_master
+
+-- echo ## assertion: master and slave tables are in sync
+-- let $diff_table_1=master:test.t1
+-- let $diff_table_2=slave:test.t1
+-- source include/diff_tables.inc
+
+--connection master
+DROP TRIGGER tr1;
+DROP TABLE t1;
+
+-- sync_slave_with_master
+

sql/item_func.cc

@@ -4766,6 +4766,7 @@ int get_var_with_binlog(THD *thd, enum_sql_command sql_command,
   user_var_event->user_var_event= var_entry;
   user_var_event->type= var_entry->type;
   user_var_event->charset_number= var_entry->collation.collation->number;
+  user_var_event->unsigned_flag= var_entry->unsigned_flag;
   if (!var_entry->value)
   {
     /* NULL value*/

sql/log.cc

@@ -4671,7 +4671,7 @@ bool MYSQL_BIN_LOG::write(Log_event *event_info)
 
             /* setting flags for user var log event */
             uchar flags= User_var_log_event::UNDEF_F;
-            if (user_var_event->user_var_event->unsigned_flag)
+            if (user_var_event->unsigned_flag)
               flags|= User_var_log_event::UNSIGNED_F;
 
             User_var_log_event e(thd, user_var_event->user_var_event->name.str,

sql/sql_class.h

@@ -75,6 +75,7 @@ typedef struct st_user_var_events
   ulong length;
   Item_result type;
   uint charset_number;
+  bool unsigned_flag;
 } BINLOG_USER_VAR_EVENT;
 
 #define RP_LOCK_LOG_IS_ALREADY_LOCKED 1