From 81e2265e7203ffb6ff16d4f22d0721aa47999e84 Mon Sep 17 00:00:00 2001
From: Mathias Jakobsen <mathias.jakobsen@overleaf.com>
Date: Mon, 14 Nov 2022 09:42:06 +0000
Subject: [PATCH] Merge pull request #10397 from
 overleaf/td-memoize-file-outline

Memoize file outline

GitOrigin-RevId: cb086bab2b6ead251362180d776e7eaff18fc639
---
 .../outline/components/outline-item.js        | 37 +++++++++---------
 .../outline/components/outline-list.js        | 38 +++++++++++++++++--
 .../outline/components/outline-root.js        |  1 +
 .../outline/components/outline-item.test.js   |  2 +
 4 files changed, 57 insertions(+), 21 deletions(-)

diff --git a/services/web/frontend/js/features/outline/components/outline-item.js b/services/web/frontend/js/features/outline/components/outline-item.js
index 928934288e..03fe4acfa0 100644
--- a/services/web/frontend/js/features/outline/components/outline-item.js
+++ b/services/web/frontend/js/features/outline/components/outline-item.js
@@ -1,4 +1,4 @@
-import { useState, useEffect, useRef } from 'react'
+import { useState, useEffect, useRef, memo } from 'react'
 import PropTypes from 'prop-types'
 import scrollIntoViewIfNeeded from 'scroll-into-view-if-needed'
 import classNames from 'classnames'
@@ -6,15 +6,13 @@ import { useTranslation } from 'react-i18next'
 import OutlineList from './outline-list'
 import Icon from '../../../shared/components/icon'
 
-function getChildrenLines(children) {
-  return (children || [])
-    .map(child => {
-      return getChildrenLines(child.children).concat(child.line)
-    })
-    .flat()
-}
-
-function OutlineItem({ outlineItem, jumpToLine, highlightedLine }) {
+const OutlineItem = memo(function OutlineItem({
+  outlineItem,
+  jumpToLine,
+  highlightedLine,
+  matchesHighlightedLine,
+  containsHighlightedLine,
+}) {
   const { t } = useTranslation()
 
   const [expanded, setExpanded] = useState(true)
@@ -25,12 +23,8 @@ function OutlineItem({ outlineItem, jumpToLine, highlightedLine }) {
     'outline-item-no-children': !outlineItem.children,
   })
 
-  const hasHighlightedChild =
-    !expanded &&
-    getChildrenLines(outlineItem.children).includes(highlightedLine)
-
-  const isHighlighted =
-    highlightedLine === outlineItem.line || hasHighlightedChild
+  const hasHighlightedChild = !expanded && containsHighlightedLine
+  const isHighlighted = matchesHighlightedLine || hasHighlightedChild
 
   const itemLinkClasses = classNames('outline-item-link', {
     'outline-item-link-highlight': isHighlighted,
@@ -90,16 +84,21 @@ function OutlineItem({ outlineItem, jumpToLine, highlightedLine }) {
         </button>
       </div>
       {expanded && outlineItem.children ? (
+        // highlightedLine is only provided to this list if the list contains
+        // the highlighted line. This means that whenever the list does not
+        // contain the highlighted line, the props provided to it are the same
+        // and the component can be memoized.
         <OutlineList
           outline={outlineItem.children}
           jumpToLine={jumpToLine}
           isRoot={false}
-          highlightedLine={highlightedLine}
+          highlightedLine={containsHighlightedLine ? highlightedLine : null}
+          containsHighlightedLine={containsHighlightedLine}
         />
       ) : null}
     </li>
   )
-}
+})
 
 OutlineItem.propTypes = {
   outlineItem: PropTypes.exact({
@@ -113,6 +112,8 @@ OutlineItem.propTypes = {
   }).isRequired,
   jumpToLine: PropTypes.func.isRequired,
   highlightedLine: PropTypes.number,
+  matchesHighlightedLine: PropTypes.bool,
+  containsHighlightedLine: PropTypes.bool,
 }
 
 export default OutlineItem
diff --git a/services/web/frontend/js/features/outline/components/outline-list.js b/services/web/frontend/js/features/outline/components/outline-list.js
index c7992235be..d7930a01a1 100644
--- a/services/web/frontend/js/features/outline/components/outline-list.js
+++ b/services/web/frontend/js/features/outline/components/outline-list.js
@@ -1,32 +1,64 @@
 import PropTypes from 'prop-types'
 import classNames from 'classnames'
 import OutlineItem from './outline-item'
+import { memo } from 'react'
 
-function OutlineList({ outline, jumpToLine, isRoot, highlightedLine }) {
+function getChildrenLines(children) {
+  return (children || [])
+    .map(child => {
+      return getChildrenLines(child.children).concat(child.line)
+    })
+    .flat()
+}
+
+const OutlineList = memo(function OutlineList({
+  outline,
+  jumpToLine,
+  isRoot,
+  highlightedLine,
+  containsHighlightedLine,
+}) {
   const listClasses = classNames('outline-item-list', {
     'outline-item-list-root': isRoot,
   })
   return (
     <ul className={listClasses} role={isRoot ? 'tree' : 'group'}>
       {outline.map((outlineItem, idx) => {
+        const matchesHighlightedLine =
+          containsHighlightedLine && highlightedLine === outlineItem.line
+        const itemContainsHighlightedLine =
+          containsHighlightedLine &&
+          getChildrenLines(outlineItem.children).includes(highlightedLine)
+
+        // highlightedLine is only provided to the item if the item matches or
+        // contains the highlighted line. This means that whenever the item does
+        // not contain the highlighted line, the props provided to it are the
+        // same and the component can be memoized.
         return (
           <OutlineItem
             key={`${outlineItem.level}-${idx}`}
             outlineItem={outlineItem}
             jumpToLine={jumpToLine}
-            highlightedLine={highlightedLine}
+            highlightedLine={
+              matchesHighlightedLine || itemContainsHighlightedLine
+                ? highlightedLine
+                : null
+            }
+            matchesHighlightedLine={matchesHighlightedLine}
+            containsHighlightedLine={itemContainsHighlightedLine}
           />
         )
       })}
     </ul>
   )
-}
+})
 
 OutlineList.propTypes = {
   outline: PropTypes.array.isRequired,
   jumpToLine: PropTypes.func.isRequired,
   isRoot: PropTypes.bool,
   highlightedLine: PropTypes.number,
+  containsHighlightedLine: PropTypes.bool,
 }
 
 export default OutlineList
diff --git a/services/web/frontend/js/features/outline/components/outline-root.js b/services/web/frontend/js/features/outline/components/outline-root.js
index 9d403ace8f..665a38e06a 100644
--- a/services/web/frontend/js/features/outline/components/outline-root.js
+++ b/services/web/frontend/js/features/outline/components/outline-root.js
@@ -14,6 +14,7 @@ function OutlineRoot({ outline, jumpToLine, highlightedLine }) {
           jumpToLine={jumpToLine}
           isRoot
           highlightedLine={highlightedLine}
+          containsHighlightedLine
         />
       ) : (
         <div className="outline-body-no-elements">
diff --git a/services/web/test/frontend/features/outline/components/outline-item.test.js b/services/web/test/frontend/features/outline/components/outline-item.test.js
index 0fdd9dd6dc..d557d395c8 100644
--- a/services/web/test/frontend/features/outline/components/outline-item.test.js
+++ b/services/web/test/frontend/features/outline/components/outline-item.test.js
@@ -54,6 +54,7 @@ describe('<OutlineItem />', function () {
         outlineItem={outlineItem}
         jumpToLine={jumpToLine}
         highlightedLine={1}
+        matchesHighlightedLine
       />
     )
 
@@ -71,6 +72,7 @@ describe('<OutlineItem />', function () {
         outlineItem={outlineItem}
         jumpToLine={jumpToLine}
         highlightedLine={2}
+        containsHighlightedLine
       />
     )