Add hint to make SDL handle dbus_shutdown()

(cherry picked from commit 2348e8b6a2598af2790937a62ee49cdb02d6bd28)

include/SDL_hints.h

@@ -2666,6 +2666,22 @@ extern "C" {
  */
 #define SDL_HINT_TRACKPAD_IS_TOUCH_ONLY "SDL_TRACKPAD_IS_TOUCH_ONLY"
 
+/**
+ * Let SDL handle dbus_shutdown().
+ *
+ * Only enable this option if no other dependency uses D-Bus.
+ *
+ * This option tells SDL that it can safely call dbus_shutdown() when
+ * SDL_Quit() is called. You must ensure that no other library still uses
+ * D-Bus when SDL_Quit() is called, otherwise resources will be freed while
+ * they are still in use, which results in undefined behavior and likely a
+ * crash.
+ *
+ * Use this option to prevent memory leaks if your application doesn't use
+ * D-Bus other than through SDL.
+ */
+#define SDL_HINT_SHUTDOWN_DBUS_ON_QUIT "SDL_SHUTDOWN_DBUS_ON_QUIT"
+
 
 /**
  *  \brief  An enumeration of hint priorities

src/SDL.c

@@ -508,13 +508,13 @@ void SDL_Quit(void)
     SDL_TicksQuit();
 #endif
 
-    SDL_ClearHints();
-    SDL_AssertionsQuit();
-
 #ifdef SDL_USE_LIBDBUS
     SDL_DBus_Quit();
 #endif
 
+    SDL_ClearHints();
+    SDL_AssertionsQuit();
+
     SDL_LogQuit();
 
     /* Now that every subsystem has been quit, we reset the subsystem refcount

src/core/linux/SDL_dbus.c

@@ -186,14 +186,12 @@ void SDL_DBus_Quit(void)
         dbus.connection_close(dbus.session_conn);
         dbus.connection_unref(dbus.session_conn);
     }
-/* Don't do this - bug 3950
-   dbus_shutdown() is a debug feature which closes all global resources in the dbus library. Calling this should be done by the app, not a library, because if there are multiple users of dbus in the process then SDL could shut it down even though another part is using it.
-*/
-#if 0
-    if (dbus.shutdown) {
+
+    SDL_bool q = SDL_GetHintBoolean(SDL_HINT_SHUTDOWN_DBUS_ON_QUIT, SDL_FALSE);
+    if (q == SDL_TRUE && dbus.shutdown) {
         dbus.shutdown();
     }
-#endif
+
     SDL_zero(dbus);
     UnloadDBUSLibrary();
     SDL_free(inhibit_handle);