fix warning

src/util/id.rs

@@ -26,6 +26,9 @@ impl<I: IdNum> IdTracker<I> {
 }
 
 impl<I: IdNum> Id<I> {
+    #[allow(dead_code)]
+    /// for debug purposes; should this be exposed?
+    /// generally you want to use labels with widgets
     pub(crate) fn raw(id: I) -> Self {
         Self(id)
     }