Fixed enabling udev hotplug detection on Linux

src/hidapi/SDL_hidapi.c

@@ -1011,6 +1011,26 @@ int SDL_hid_init(void)
         return 0;
     }
 
+#if defined(SDL_USE_LIBUDEV)
+    if (SDL_getenv("SDL_HIDAPI_JOYSTICK_DISABLE_UDEV") != NULL) {
+        SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
+                     "udev disabled by SDL_HIDAPI_JOYSTICK_DISABLE_UDEV");
+        linux_enumeration_method = ENUMERATION_FALLBACK;
+    } else if (access("/.flatpak-info", F_OK) == 0
+               || access("/run/host/container-manager", F_OK) == 0) {
+        /* Explicitly check `/.flatpak-info` because, for old versions of
+         * Flatpak, this was the only available way to tell if we were in
+         * a Flatpak container. */
+        SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
+                     "Container detected, disabling HIDAPI udev integration");
+        linux_enumeration_method = ENUMERATION_FALLBACK;
+    } else {
+        SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
+                     "Using udev for HIDAPI joystick device discovery");
+        linux_enumeration_method = ENUMERATION_LIBUDEV;
+    }
+#endif
+
 #ifdef SDL_LIBUSB_DYNAMIC
     ++attempts;
     libusb_ctx.libhandle = SDL_LoadObject(SDL_LIBUSB_DYNAMIC);