Bug#45498: Socket variable not available on Windows

The "socket" variable is not available on Windows even though
the --socket option can be used to specify the pipe name for
local connections that use a named pipe.

The solution is to ensure that the variable is always defined.

mysql-test/r/windows.result

@@ -53,3 +53,10 @@ ERROR HY000: No paths allowed for shared library
 execute abc;
 ERROR HY000: No paths allowed for shared library
 deallocate prepare abc;
+#
+# Bug#45498: Socket variable not available on Windows
+#
+SELECT VARIABLE_NAME FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES
+WHERE VARIABLE_NAME = 'socket';
+VARIABLE_NAME
+SOCKET

mysql-test/t/windows.test

@@ -92,3 +92,9 @@ execute abc;
 execute abc;
 deallocate prepare abc;
 
+--echo #
+--echo # Bug#45498: Socket variable not available on Windows
+--echo #
+
+SELECT VARIABLE_NAME FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES
+  WHERE VARIABLE_NAME = 'socket';

sql/set_var.cc

@@ -529,11 +529,11 @@ static sys_var_const    sys_skip_networking(&vars, "skip_networking",
 static sys_var_const    sys_skip_show_database(&vars, "skip_show_database",
                                             OPT_GLOBAL, SHOW_BOOL,
                                             (uchar*) &opt_skip_show_db);
-#ifdef HAVE_SYS_UN_H
+
 static sys_var_const    sys_socket(&vars, "socket",
                                    OPT_GLOBAL, SHOW_CHAR_PTR,
                                    (uchar*) &mysqld_unix_port);
-#endif
+
 #ifdef HAVE_THR_SETCONCURRENCY
 /* purecov: begin tested */
 static sys_var_const    sys_thread_concurrency(&vars, "thread_concurrency",