MDEV-7780 - Support for faking server version

Added --version=str (optional argument sets server version string).

mysql-test/r/mysqld--help.result

@@ -1124,7 +1124,8 @@ The following options may be given as the first argument:
  CLIENT_STATISTICS, INDEX_STATISTICS and TABLE_STATISTICS
  tables in the INFORMATION_SCHEMA
  -v, --verbose       Used with --help option for detailed help.
- -V, --version       Output version information and exit.
+ -V, --version[=name] 
+ Output version information and exit.
  --wait-timeout=#    The number of seconds the server waits for activity on a
  connection before closing it
 

mysql-test/suite/sys_vars/r/version.result

+SELECT @@version;
+@@version
+my_favorite_version
+1

mysql-test/suite/sys_vars/t/version.opt

+--version="my_favorite_version"

mysql-test/suite/sys_vars/t/version.test

+SELECT @@version;
+perl;
+  $cnt= grep /my_favorite_version/, `$ENV{MYSQL} -e status`;
+  print "$cnt\n";
+EOF

sql/mysqld.cc

@@ -631,7 +631,7 @@ DATE_TIME_FORMAT global_date_format, global_datetime_format, global_time_format;
 Time_zone *default_tz;
 
 const char *mysql_real_data_home_ptr= mysql_real_data_home;
-char server_version[SERVER_VERSION_LENGTH];
+char server_version[SERVER_VERSION_LENGTH], *server_version_ptr;
 char *mysqld_unix_port, *opt_mysql_tmpdir;
 ulong thread_handling;
 
@@ -7604,8 +7604,8 @@ struct my_option my_long_options[]=
    0, 0, 0, 0, 0, 0},
   {"verbose", 'v', "Used with --help option for detailed help.",
    &opt_verbose, &opt_verbose, 0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
-  {"version", 'V', "Output version information and exit.", 0, 0, 0, GET_NO_ARG,
-   NO_ARG, 0, 0, 0, 0, 0, 0},
+  {"version", 'V', "Output version information and exit.", 0, 0, 0, GET_STR,
+   OPT_ARG, 0, 0, 0, 0, 0, 0},
   {"plugin-load", OPT_PLUGIN_LOAD,
    "Semicolon-separated list of plugins to load, where each plugin is "
    "specified as ether a plugin_name=library_file pair or only a library_file. "
@@ -8947,8 +8947,16 @@ mysqld_get_one_option(int optid, const struct my_option *opt, char *argument)
 #include <sslopt-case.h>
 #ifndef EMBEDDED_LIBRARY
   case 'V':
+    if (argument)
+    {
+      strmake(server_version, argument, sizeof(server_version) - 1);
+      set_sys_var_value_origin(&server_version_ptr, sys_var::CONFIG);
+    }
+    else
+    {
       print_version();
       opt_abort= 1;                    // Abort after parsing all options
+    }
     break;
 #endif /*EMBEDDED_LIBRARY*/
   case 'W':
@@ -9641,6 +9649,8 @@ static int get_options(int *argc_ptr, char ***argv_ptr)
 
 void set_server_version(void)
 {
+  if (!IS_SYSVAR_AUTOSIZE(&server_version_ptr))
+    return;
   char *end= strxmov(server_version, MYSQL_SERVER_VERSION,
                      MYSQL_SERVER_SUFFIX_STR, NullS);
 #ifdef EMBEDDED_LIBRARY

sql/mysqld.h

@@ -534,6 +534,7 @@ extern uint mysql_real_data_home_len;
 extern const char *mysql_real_data_home_ptr;
 extern ulong thread_handling;
 extern "C" MYSQL_PLUGIN_IMPORT char server_version[SERVER_VERSION_LENGTH];
+extern char *server_version_ptr;
 extern MYSQL_PLUGIN_IMPORT char mysql_real_data_home[];
 extern char mysql_unpacked_real_data_home[];
 extern MYSQL_PLUGIN_IMPORT struct system_variables global_system_variables;

sql/sys_vars.cc

@@ -3368,7 +3368,6 @@ static Sys_var_mybool Sys_timed_mutexes(
        NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL), ON_UPDATE(NULL),
        DEPRECATED(""));
 
-static char *server_version_ptr;
 static Sys_var_charptr Sys_version(
        "version", "Server version",
        READ_ONLY GLOBAL_VAR(server_version_ptr),