From b91026fa895d4aef1627d48864fa9fd2807cc666 Mon Sep 17 00:00:00 2001
From: Travis Ralston <travpc@gmail.com>
Date: Mon, 27 Jul 2020 17:18:01 -0600
Subject: [PATCH] Ensure CustomRoomTagStore doesn't fire useless updates

This could in theory cause double rendering of the room list under some conditions.
---
 src/stores/CustomRoomTagStore.js |  8 ++++++--
 src/utils/objects.ts             | 17 +++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/stores/CustomRoomTagStore.js b/src/stores/CustomRoomTagStore.js
index 9967708c29..1f24dc589a 100644
--- a/src/stores/CustomRoomTagStore.js
+++ b/src/stores/CustomRoomTagStore.js
@@ -22,6 +22,7 @@ import SettingsStore from "../settings/SettingsStore";
 import RoomListStore, {LISTS_UPDATE_EVENT} from "./room-list/RoomListStore";
 import {RoomNotificationStateStore} from "./notifications/RoomNotificationStateStore";
 import {isCustomTag} from "./room-list/models";
+import {objectHasDiff} from "../utils/objects";
 
 function commonPrefix(a, b) {
     const len = Math.min(a.length, b.length);
@@ -107,7 +108,10 @@ class CustomRoomTagStore extends EventEmitter {
     }
 
     _onListsUpdated = () => {
-        this._setState({tags: this._getUpdatedTags()});
+        const newTags = this._getUpdatedTags();
+        if (!this._state.tags || objectHasDiff(this._state.tags, newTags)) {
+            this._setState({tags: newTags});
+        }
     };
 
     _onDispatch(payload) {
@@ -134,7 +138,7 @@ class CustomRoomTagStore extends EventEmitter {
 
     _getUpdatedTags() {
         if (!SettingsStore.isFeatureEnabled("feature_custom_tags")) {
-            return;
+            return {}; // none
         }
 
         const newTagNames = Object.keys(RoomListStore.instance.orderedLists).filter(t => isCustomTag(t)).sort();
diff --git a/src/utils/objects.ts b/src/utils/objects.ts
index db8248759d..9dcc41ecd2 100644
--- a/src/utils/objects.ts
+++ b/src/utils/objects.ts
@@ -72,6 +72,23 @@ export function objectHasValueChange(a: any, b: any): boolean {
     return arrayHasDiff(aValues, bValues);
 }
 
+/**
+ * Determines if any keys were added, removed, or changed between two objects.
+ * For changes, simple triple equal comparisons are done, not in-depth
+ * tree checking.
+ * @param a The first object. Must be defined.
+ * @param b The second object. Must be defined.
+ * @returns True if there's a difference between the objects, false otherwise
+ */
+export function objectHasDiff(a: any, b: any): boolean {
+    const aKeys = Object.keys(a);
+    const bKeys = Object.keys(b);
+    if (arrayHasDiff(aKeys, bKeys)) return true;
+
+    const possibleChanges = arrayUnion(aKeys, bKeys);
+    return possibleChanges.some(k => a[k] !== b[k]);
+}
+
 /**
  * Determines the keys added, changed, and removed between two objects.
  * For changes, simple triple equal comparisons are done, not in-depth