This patch ensures '.desktop' files are picked up in the system profile
and not in the directories listed in $XDG_DATA_DIRS.  The latter includes
'gnome-session.desktop', which should be used if it's in
/run/current-system/profile, and only then.

Fixes <https://bugs.gnu.org/37831>.
--- a/daemon/gdm-session.c	2021-07-23 15:16:15.164201000 +0000
+++ b/daemon/gdm-session.c	2021-09-26 08:18:58.730134555 +0000
@@ -354,25 +354,19 @@
         GArray *search_array = NULL;
         char **search_dirs;
         int i;
-        const gchar * const *system_data_dirs = g_get_system_data_dirs ();
 
         static const char *x_search_dirs[] = {
                 "/etc/X11/sessions/",
                 DMCONFDIR "/Sessions/",
                 DATADIR "/gdm/BuiltInSessions/",
-                DATADIR "/xsessions/",
+                "/run/current-system/profile/share/xsessions/",
         };
 
-        static const char *wayland_search_dir = DATADIR "/wayland-sessions/";
+        static const char *wayland_search_dir = "/run/current-system/profile/share/wayland-sessions/";
 
         search_array = g_array_new (TRUE, TRUE, sizeof (char *));
 
         if (type == NULL || g_str_equal (type, "x11")) {
-                for (i = 0; system_data_dirs[i]; i++) {
-                        gchar *dir = g_build_filename (system_data_dirs[i], "xsessions", NULL);
-                        g_array_append_val (search_array, dir);
-                }
-
                 g_array_append_vals (search_array, x_search_dirs, G_N_ELEMENTS (x_search_dirs));
         }
 
@@ -382,16 +376,7 @@
 #ifdef ENABLE_USER_DISPLAY_SERVER
                 g_array_prepend_val (search_array, wayland_search_dir);
 
-                for (i = 0; system_data_dirs[i]; i++) {
-                        gchar *dir = g_build_filename (system_data_dirs[i], "wayland-sessions", NULL);
-                        g_array_insert_val (search_array, i, dir);
-                }
 #else
-                for (i = 0; system_data_dirs[i]; i++) {
-                        gchar *dir = g_build_filename (system_data_dirs[i], "wayland-sessions", NULL);
-                        g_array_append_val (search_array, dir);
-                }
-
                 g_array_append_val (search_array, wayland_search_dir);
 #endif
         }
diff -ur a/libgdm/gdm-sessions.c b/libgdm/gdm-sessions.c
--- a/libgdm/gdm-sessions.c	2019-10-07 04:53:35.000000000 -0400
+++ b/libgdm/gdm-sessions.c	2020-04-18 18:31:42.491348691 -0400
@@ -245,35 +245,23 @@
                 "/etc/X11/sessions/",
                 DMCONFDIR "/Sessions/",
                 DATADIR "/gdm/BuiltInSessions/",
-                DATADIR "/xsessions/",
+                "/run/current-system/profile/share/xsessions/"
         };
 
         names_seen_before = g_hash_table_new (g_str_hash, g_str_equal);
         xorg_search_array = g_ptr_array_new_with_free_func (g_free);
 
-        const gchar * const *system_data_dirs = g_get_system_data_dirs ();
-
-        for (i = 0; system_data_dirs[i]; i++) {
-                session_dir = g_build_filename (system_data_dirs[i], "xsessions", NULL);
-                g_ptr_array_add (xorg_search_array, session_dir);
-        }
-
         for (i = 0; i < G_N_ELEMENTS (xorg_search_dirs); i++) {
                 g_ptr_array_add (xorg_search_array, g_strdup (xorg_search_dirs[i]));
         }
 
 #ifdef ENABLE_WAYLAND_SUPPORT
         const char *wayland_search_dirs[] = {
-                DATADIR "/wayland-sessions/",
+                "/run/current-system/profile/share/wayland-sessions/",
         };
 
         wayland_search_array = g_ptr_array_new_with_free_func (g_free);
 
-        for (i = 0; system_data_dirs[i]; i++) {
-                session_dir = g_build_filename (system_data_dirs[i], "wayland-sessions", NULL);
-                g_ptr_array_add (wayland_search_array, session_dir);
-        }
-
         for (i = 0; i < G_N_ELEMENTS (wayland_search_dirs); i++) {
                 g_ptr_array_add (wayland_search_array, g_strdup (wayland_search_dirs[i]));
         }