Fix for BUG#51215 "log-error partially works with version 5.5": WL 4738 (reengineering of server variables)

had broken the 5.1 behaviour of --log-error: --log-error without argument sent to stderr instead of writing
to a file with an autogenerated name.

mysql-test/suite/sys_vars/t/log_error_func.test:
  test that error log is created and shown in SHOW VARIABLES.
  Interestingly the error log's path is apparently relative if --log-error=argument is used, but
  may be absolute or relative if --log-error(no argument) is used (because then the path is derived from
  that of pidfile_name, which can be absolute or relative, depending on if autogenerated or not).
mysql-test/suite/sys_vars/t/log_error_func2.test:
  test that error log is created and shown in SHOW VARIABLES
mysql-test/suite/sys_vars/t/log_error_func3.test:
  test that error log is empty in SHOW VARIABLES
sql/mysql_priv.h:
  id for option --log-error
sql/mysqld.cc:
  No --log-error means "write errors to stderr", whereas --log-error
  without argument means "write errors to a file". So we cannot use the default logic
  of class sys_var_charptr, which treats "option not used" the same as "option used
  without argument" and uses the same default for both. We need to catch "option used",
  in mysqld_get_one_option(), and then "without argument". Setting to "" makes sure
  that init_server_components() will create the log, with an autogenerated name.
sql/sys_vars.cc:
  need to give the option a numeric id so that we can catch it in mysqld_get_one_option()

1 files changed, 13 insertions, 0 deletions

diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index 2e908eb3366..37713992a90 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -3962,6 +3962,11 @@ static int init_server_components()
     else
       fn_format(log_error_file, log_error_file_ptr, mysql_data_home, ".err",
                 MY_UNPACK_FILENAME | MY_SAFE_PATH);
+    /*
+      _ptr may have been set to my_disabled_option or "" if no argument was
+      passed, but we need to show the real name in SHOW VARIABLES:
+    */
+    log_error_file_ptr= log_error_file;
     if (!log_error_file[0])
       opt_error_log= 0;                         // Too long file name
     else
@@ -7357,6 +7362,14 @@ mysqld_get_one_option(int optid,
       global_system_variables.optimizer_switch&=
         ~OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN;
     break;
+  case OPT_LOG_ERROR:
+    /*
+      "No --log-error" == "write errors to stderr",
+      "--log-error without argument" == "write errors to a file".
+    */
+    if (argument == NULL) /* no argument */
+      log_error_file_ptr= const_cast<char*>("");
+    break;
   }
   return 0;
 }