From c320d2364ed4c3c24ca3163f535e1090d4968601 Mon Sep 17 00:00:00 2001
From: Kenichi Kobayashi <ken1kob@users.noreply.github.com>
Date: Wed, 8 Jun 2022 18:33:53 +0900
Subject: [PATCH] Performance: suppresses redundant SideBar re-rendering on
 state.tags (#6451)

---
 packages/lib/reducer.test.js | 22 ++++++++++++++++++++++
 packages/lib/reducer.ts      |  7 +++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/packages/lib/reducer.test.js b/packages/lib/reducer.test.js
index 1e9d9b7a6..85b6b5326 100644
--- a/packages/lib/reducer.test.js
+++ b/packages/lib/reducer.test.js
@@ -610,4 +610,26 @@ describe('reducer', function() {
 			expect(state.selectedNoteIds).toBe(expected);
 		}
 	});
+
+	// tests for TAG_UPDATE_ALL about PR #6451
+	it('should not change tags when a new value is deep equal to the old value', async () => {
+		const tags = await createNTestTags(6);
+		const oldTags = tags.slice(0, 5);
+		{
+			// Case 1. The input which is deep equal to the current state.tags doesn't change state.tags.
+			const oldState = initTestState(null, null, null, null, oldTags, [2]);
+			const newTags = oldTags.slice();
+			// test action
+			const newState = reducer(oldState, { type: 'TAG_UPDATE_ALL', items: newTags });
+			expect(newState.tags).toBe(oldState.tags);
+		}
+		{
+			// Case 2. A different input changes state.tags.
+			const oldState = initTestState(null, null, null, null, oldTags, [2]);
+			const newTags = oldTags.slice().splice(3, 1, tags[5]);
+			// test action
+			const newState = reducer(oldState, { type: 'TAG_UPDATE_ALL', items: newTags });
+			expect(newState.tags).not.toBe(oldState.tags);
+		}
+	});
 });
diff --git a/packages/lib/reducer.ts b/packages/lib/reducer.ts
index 9314fe2c8..58b9b533b 100644
--- a/packages/lib/reducer.ts
+++ b/packages/lib/reducer.ts
@@ -1,4 +1,4 @@
-import produce, { Draft } from 'immer';
+import produce, { Draft, original } from 'immer';
 import pluginServiceReducer, { stateRootKey as pluginServiceStateRootKey, defaultState as pluginServiceDefaultState, State as PluginServiceState } from './services/plugins/reducer';
 import shareServiceReducer, { stateRootKey as shareServiceStateRootKey, defaultState as shareServiceDefaultState, State as ShareServiceState } from './services/share/reducer';
 import Note from './models/Note';
@@ -7,6 +7,7 @@ import BaseModel from './BaseModel';
 import { Store } from 'redux';
 import { ProfileConfig } from './services/profileConfig/types';
 import * as ArrayUtils from './ArrayUtils';
+const fastDeepEqual = require('fast-deep-equal');
 const { ALL_NOTES_FILTER_ID } = require('./reserved-ids');
 const { createSelectorCreator, defaultMemoize } = require('reselect');
 const { createCachedSelector } = require('re-reselect');
@@ -924,7 +925,9 @@ const reducer = produce((draft: Draft<State> = defaultState, action: any) => {
 			break;
 
 		case 'TAG_UPDATE_ALL':
-			draft.tags = action.items;
+			if (!fastDeepEqual(original(draft.tags), action.items)) {
+				draft.tags = action.items;
+			}
 			break;
 
 		case 'TAG_SELECT':