MDEV-6435: Assertion `m_status == DA_ERROR' failed in Diagnostics_area::sql_errno() with parallel replication

When a MyISAM query is killed midway, the query is logged to the binlog marked
with the error.

The slave does not attempt to run the query, but aborts with a suitable error
message in the error log for the DBA to act on.

In this case, the parallel replication code would check the sql_errno() code,
even no my_error() had been set. In debug builds, this causes an assertion.

Fixed the code to check that we actually have an error set before querying for
an error code.

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

@@ -819,11 +819,37 @@ test_check
 OK
 test_check
 OK
+*** MDEV_6435: Incorrect error handling when query binlogged partially on master with "killed" error ***
+CREATE TABLE t6 (a INT) ENGINE=MyISAM;
+CREATE TRIGGER tr AFTER INSERT ON t6 FOR EACH ROW SET @a = 1;
+SET @old_format= @@binlog_format;
+SET binlog_format= statement;
+SET debug_sync='sp_head_execute_before_loop SIGNAL ready WAIT_FOR cont';
+INSERT INTO t6 VALUES (1), (2), (3);
+SET debug_sync='now WAIT_FOR ready';
+KILL QUERY CONID;
+SET debug_sync='now SIGNAL cont';
+ERROR 70100: Query execution was interrupted
+SET binlog_format= @old_format;
+SET debug_sync='RESET';
+SET debug_sync='RESET';
+include/wait_for_slave_sql_error.inc [errno=1317]
+STOP SLAVE IO_THREAD;
+SET GLOBAL gtid_slave_pos= 'AFTER_ERROR_GTID_POS';
+include/start_slave.inc
+INSERT INTO t6 VALUES (4);
+SELECT * FROM t6 ORDER BY a;
+a
+1
+4
+SELECT * FROM t6 ORDER BY a;
+a
+4
 include/stop_slave.inc
 SET GLOBAL slave_parallel_threads=@old_parallel_threads;
 include/start_slave.inc
 SET DEBUG_SYNC= 'RESET';
 DROP function foo;
-DROP TABLE t1,t2,t3,t4,t5;
+DROP TABLE t1,t2,t3,t4,t5,t6;
 SET DEBUG_SYNC= 'RESET';
 include/rpl_end.inc

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

@@ -1292,6 +1292,54 @@ eval SELECT IF('$io_pos' = '$sql_pos', "OK", "Not ok, $io_pos <> $sql_pos") AS t
 --enable_query_log
 
 
+--echo *** MDEV_6435: Incorrect error handling when query binlogged partially on master with "killed" error ***
+
+--connection server_1
+CREATE TABLE t6 (a INT) ENGINE=MyISAM;
+CREATE TRIGGER tr AFTER INSERT ON t6 FOR EACH ROW SET @a = 1;
+
+--connection con1
+SET @old_format= @@binlog_format;
+SET binlog_format= statement;
+--let $conid = `SELECT CONNECTION_ID()`
+SET debug_sync='sp_head_execute_before_loop SIGNAL ready WAIT_FOR cont';
+send INSERT INTO t6 VALUES (1), (2), (3);
+
+--connection server_1
+SET debug_sync='now WAIT_FOR ready';
+--replace_result $conid CONID
+eval KILL QUERY $conid;
+SET debug_sync='now SIGNAL cont';
+
+--connection con1
+--error ER_QUERY_INTERRUPTED
+--reap
+SET binlog_format= @old_format;
+SET debug_sync='RESET';
+--let $after_error_gtid_pos= `SELECT @@gtid_binlog_pos`
+
+--connection server_1
+SET debug_sync='RESET';
+
+
+--connection server_2
+--let $slave_sql_errno= 1317
+--source include/wait_for_slave_sql_error.inc
+STOP SLAVE IO_THREAD;
+--replace_result $after_error_gtid_pos AFTER_ERROR_GTID_POS
+eval SET GLOBAL gtid_slave_pos= '$after_error_gtid_pos';
+--source include/start_slave.inc
+
+--connection server_1
+INSERT INTO t6 VALUES (4);
+SELECT * FROM t6 ORDER BY a;
+--save_master_pos
+
+--connection server_2
+--sync_with_master
+SELECT * FROM t6 ORDER BY a;
+
+
 --connection server_2
 --source include/stop_slave.inc
 SET GLOBAL slave_parallel_threads=@old_parallel_threads;
@@ -1300,7 +1348,7 @@ SET DEBUG_SYNC= 'RESET';
 
 --connection server_1
 DROP function foo;
-DROP TABLE t1,t2,t3,t4,t5;
+DROP TABLE t1,t2,t3,t4,t5,t6;
 SET DEBUG_SYNC= 'RESET';
 
 --source include/rpl_end.inc

sql/rpl_parallel.cc

@@ -234,8 +234,11 @@ static void
 convert_kill_to_deadlock_error(rpl_group_info *rgi)
 {
   THD *thd= rgi->thd;
-  int err_code= thd->get_stmt_da()->sql_errno();
+  int err_code;
 
+  if (!thd->get_stmt_da()->is_error())
+    return;
+  err_code= thd->get_stmt_da()->sql_errno();
   if ((err_code == ER_QUERY_INTERRUPTED || err_code == ER_CONNECTION_KILLED) &&
       rgi->killed_for_retry)
   {

sql/sp_head.cc

@@ -43,6 +43,7 @@
 #include "sql_base.h"                           // close_thread_tables
 #include "transaction.h"       // trans_commit_stmt
 #include "sql_audit.h"
+#include "debug_sync.h"
 
 /*
   Sufficient max length of printed destinations and frame offsets (all uints).
@@ -1309,6 +1310,7 @@ sp_head::execute(THD *thd, bool merge_da_on_success)
   /* Discard the initial part of executing routines. */
   thd->profiling.discard_current_query();
 #endif
+  DEBUG_SYNC(thd, "sp_head_execute_before_loop");
   do
   {
     sp_instr *i;