Bug#43835: SHOW VARIABLES does not include 0 for slave_skip_errors

We didn't expect "error: no error", although this is
in fact a legitimate state (if something is erroneous
on the master, but not on the slave, e.g. INSERT fails
on master due to UNIQUE constraint which does not exist
on slave).

We now list the ignore for "0: no error" the same way
as any other ignore; moreover, if no or an empty
--slave-skip-errors is passed at start-up, we show
"OFF" instead of empty list, as intended. (The code
for that was there, but was only run for the empty-
argument case, even if it subsequently tested for
both conditions.) 

mysql-test/r/not_embedded_server.result:
  Show that passing no --slave-skip-errors results
  in "OFF" being shown as the variable's value. This
  test's "twin" (also not embedded, but setting
  --slave-skip-errors in its -opt file) lives in
  variables-notembbeded.test.
mysql-test/r/variables-notembedded.result:
  Show that error-ignore 0 is handled just like any other
  ignore. This test's "twin" (also not embedded, but not
  setting --slave-skip-errors in its -opt file) lives in
  not_embbeded_server.test.
mysql-test/t/not_embedded_server.test:
  Show that passing no --slave-skip-errors results
  in "OFF" being shown as the variable's value.
mysql-test/t/variables-notembedded-master.opt:
  Show that error-ignore 0 is handled just like any other
  ignore.
sql/slave.cc:
  - set up error-ignore-info even if --slave-skip-errors
    was not passed at start-up.
  
  - handle error 0 just like any other error.

mysql-test/r/not_embedded_server.result

 select 1;
 1
 1
+SHOW VARIABLES like 'slave_skip_errors';
+Variable_name	Value
+slave_skip_errors	OFF

mysql-test/r/variables-notembedded.result

@@ -11,7 +11,7 @@ Variable_name	Value
 slave_load_tmpdir	SLAVE_LOAD_TMPDIR
 show variables like 'slave_skip_errors';
 Variable_name	Value
-slave_skip_errors	3,100,137,643,1752
+slave_skip_errors	0,3,100,137,643,1752
 ---- Clean Up ----
 set global slave_net_timeout=default;
 set global sql_slave_skip_counter= 0;
@@ -98,12 +98,12 @@ ERROR HY000: Variable 'slave_load_tmpdir' is a read only variable
 #
 SHOW VARIABLES like 'slave_skip_errors';
 Variable_name	Value
-slave_skip_errors	3,100,137,643,1752
+slave_skip_errors	0,3,100,137,643,1752
 SELECT @@session.slave_skip_errors;
 ERROR HY000: Variable 'slave_skip_errors' is a GLOBAL variable
 SELECT @@global.slave_skip_errors;
 @@global.slave_skip_errors
-3,100,137,643,1752
+0,3,100,137,643,1752
 SET @@session.slave_skip_errors= 7;
 ERROR HY000: Variable 'slave_skip_errors' is a read only variable
 SET @@global.slave_skip_errors= 7;

mysql-test/t/not_embedded_server.test

@@ -36,4 +36,10 @@ select 1;
 #execute stmt1;
 #deallocate prepare stmt1;
 
+#
+# Bug#43835: SHOW VARIABLES does not include 0 for slave_skip_errors
+#
+
+SHOW VARIABLES like 'slave_skip_errors';
+
 # End of 5.1 tests

mysql-test/t/variables-notembedded-master.opt

---loose-slave-skip-errors=3,100,137,643,1752
+--loose-slave-skip-errors=3,100,137,0,643,1752

sql/slave.cc

@@ -128,6 +128,7 @@ static bool wait_for_relay_log_space(Relay_log_info* rli);
 static inline bool io_slave_killed(THD* thd,Master_info* mi);
 static inline bool sql_slave_killed(THD* thd,Relay_log_info* rli);
 static int init_slave_thread(THD* thd, SLAVE_THD_TYPE thd_type);
+static void print_slave_skip_errors(void);
 static int safe_connect(THD* thd, MYSQL* mysql, Master_info* mi);
 static int safe_reconnect(THD* thd, MYSQL* mysql, Master_info* mi,
                           bool suppress_warnings);
@@ -231,6 +232,15 @@ int init_slave()
   */
   active_mi= new Master_info;
 
+  /*
+    If --slave-skip-errors=... was not used, the string value for the
+    system variable has not been set up yet. Do it now.
+  */
+  if (!use_slave_mask)
+  {
+    print_slave_skip_errors();
+  }
+
   /*
     If master_host is not specified, try to read it from the master_info file.
     If master_host is specified, create the master_info file if it doesn't
@@ -311,7 +321,7 @@ static void print_slave_skip_errors(void)
     char *bend= buff + sizeof(slave_skip_error_names);
     int  errnum;
 
-    for (errnum= 1; errnum < MAX_SLAVE_ERROR; errnum++)
+    for (errnum= 0; errnum < MAX_SLAVE_ERROR; errnum++)
     {
       if (bitmap_is_set(&slave_error_mask, errnum))
       {