From af07de5d8e3e8b9cf4be5ad7143286840a8a619c Mon Sep 17 00:00:00 2001
From: Dustin Carlino <dabreegster@gmail.com>
Date: Tue, 19 Jan 2021 11:27:56 -0800
Subject: [PATCH] Fix deserializing a map in JSON. #392

---
 map_model/src/pathfind/node_map.rs | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/map_model/src/pathfind/node_map.rs b/map_model/src/pathfind/node_map.rs
index 878cbe59f7..18e8cc3557 100644
--- a/map_model/src/pathfind/node_map.rs
+++ b/map_model/src/pathfind/node_map.rs
@@ -6,9 +6,12 @@ use std::fmt::Debug;
 use fast_paths::{NodeId, ShortestPath};
 use serde::{Deserialize, Deserializer, Serialize};
 
+/// A bidirectional mapping between fast_paths NodeId and some custom ID type.
 // TODO Upstream this in fast_paths when this is more solid.
 #[derive(Serialize)]
 pub struct NodeMap<T: Copy + Ord + Debug + Serialize> {
+    // These two fields are redundant and large, so don't serialize the bigger one, to cut down
+    // file size.
     #[serde(skip_serializing)]
     node_to_id: BTreeMap<T, NodeId>,
     id_to_node: Vec<T>,
@@ -48,7 +51,12 @@ impl<T: Copy + Ord + Debug + Serialize> NodeMap<T> {
     }
 }
 
-// TODO Still can't figure out how to derive Deserialize on NodeMap directly.
+// A serialized NodeMap has this form in JSON. Use this to deserialize.
+#[derive(Deserialize)]
+struct InnerNodeMap<T: Copy + Ord + Debug> {
+    id_to_node: Vec<T>,
+}
+
 pub fn deserialize_nodemap<
     'de,
     D: Deserializer<'de>,
@@ -56,9 +64,8 @@ pub fn deserialize_nodemap<
 >(
     d: D,
 ) -> Result<NodeMap<T>, D::Error> {
-    // TODO I'm offline and can't look up hw to use Deserializer twice in sequence. Since the two
-    // fields are redundant, just serialize one of them.
-    let id_to_node = <Vec<T>>::deserialize(d)?;
+    let inner = <InnerNodeMap<T>>::deserialize(d)?;
+    let id_to_node = inner.id_to_node;
     let mut node_to_id = BTreeMap::new();
     for (id, node) in id_to_node.iter().enumerate() {
         node_to_id.insert(*node, id);