Allow (temporarilly) unused LinkedList::const_new

tokio/src/util/linked_list.rs

@@ -71,6 +71,8 @@ unsafe impl<T: Sync> Sync for Pointers<T> {}
 // ===== impl LinkedList =====
 
 impl<L, T> LinkedList<L, T> {
+    /// Constant constructor for a `LinkedList`.
+    #[allow(dead_code)] // NOTE: This will get removed with: https://github.com/tokio-rs/tokio/pull/2790
     pub(crate) const fn const_new() -> LinkedList<L, T> {
         LinkedList {
             head: None,
@@ -325,6 +327,11 @@ mod tests {
         }};
     }
 
+    #[test]
+    fn const_new() {
+        const _: LinkedList<&Entry, <&Entry as Link>::Target> = LinkedList::const_new();
+    }
+
     #[test]
     fn push_and_drain() {
         let a = entry(5);