Handle removing a node, and a shard disconnecting (bulk remove)

backend/common/src/assign_id.rs

@@ -1,4 +1,4 @@
-use std::hash::Hash;
+use std::{fmt::Display, hash::Hash};
 use serde::{Serialize,Deserialize};
 use bimap::BiMap;
 
@@ -15,6 +15,11 @@ impl std::convert::From<usize> for Id {
         Id(n)
     }
 }
+impl Display for Id {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
 
 /// A struct that allows you to assign an ID to an arbitrary set of
 /// details (so long as they are Eq+Hash+Clone), and then access

backend/common/src/most_seen.rs

@@ -10,7 +10,13 @@ pub struct MostSeen<T> {
     others: HashMap<T, usize>
 }
 
-impl <T: Hash + Eq> MostSeen<T> {
+impl <T: Default> Default for MostSeen<T> {
+    fn default() -> Self {
+        MostSeen::new(T::default())
+    }
+}
+
+impl <T> MostSeen<T> {
     pub fn new(item: T) -> Self {
         Self {
             current_best: item,

backend/common/src/util/dense_map.rs

@@ -77,4 +77,16 @@ impl<T> DenseMap<T> {
     pub fn is_empty(&self) -> bool {
         self.len() == 0
     }
+
+    /// Return the next Id that will be assigned.
+    pub fn next_id(&self) -> usize {
+        match self.retired.last() {
+            Some(id) => {
+                *id
+            }
+            None => {
+                self.items.len()
+            }
+        }
+    }
 }