camera: Document why we currently use the empty app id for host apps

The app id detection is still unreliable and some backends do check if
the window matches the app id. Because that app id for host apps comes
from the app itself through wayland, the checks can fail.

For now we just disable app id detection for host apps for the camera
portal entirely. This should be removed when app id detection has become
more reliable.

src/camera.c

@@ -78,6 +78,11 @@ query_permission_sync (XdpRequest *request)
   const char *app_id;
   gboolean allowed;
 
+  /* The app id detection is still unreliable and some backends do check if the
+   * window matches the app id. Because that app id for host apps comes from the
+   * app itself through wayland, the checks can fail.
+   * This should be removed when app id detection has become more reliable.
+   */
   if (xdp_app_info_is_host (request->app_info))
     app_id = "";
   else

tests/camera.c

@@ -19,15 +19,21 @@ extern gchar *appid;
 static void
 set_camera_permissions (const char *permission)
 {
+  const char *permission_app_id;
   const char *permissions[2] = { NULL, NULL };
   g_autoptr(GError) error = NULL;
 
+  /* x-d-p currently defaults to the empty app id for the camera portal for
+   * host XdpAppInfos (which the XdpAppInfoTest is). So instead of using the
+   * `extern gchar *appid` we have to use "" for now. */
+  permission_app_id = "";
+
   permissions[0] = permission;
   xdp_dbus_impl_permission_store_call_set_permission_sync (permission_store,
                                                            "devices",
                                                            TRUE,
                                                            "camera",
-                                                           "",
+                                                           permission_app_id,
                                                            permissions,
                                                            NULL,
                                                            &error);