From fb6f131fa1845e8d0d46a3d58ac93bc09afc1f14 Mon Sep 17 00:00:00 2001
From: Thibaut Girka <thib@sitedethib.com>
Date: Sat, 10 Feb 2018 20:56:48 +0100
Subject: [PATCH] Revert 245816ab2721f386184878d71be01143d207abf5 (fixes #348)

Since 245816ab2721f386184878d71be01143d207abf5, IntersectionObserverArticle
assumes that its children do not change unless the number of children changes.

This is not the case with the notification overlay, which resulted in the
checkmark of notification cleaning mode not updating unless scrolling to make
notifications appear/disappear.

This change may negatively impact performances.
---
 .../intersection_observer_article.js          | 26 +++++++++----------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/app/javascript/flavours/glitch/components/intersection_observer_article.js b/app/javascript/flavours/glitch/components/intersection_observer_article.js
index 8b06f9a8c..f7f6b0a53 100644
--- a/app/javascript/flavours/glitch/components/intersection_observer_article.js
+++ b/app/javascript/flavours/glitch/components/intersection_observer_article.js
@@ -1,15 +1,10 @@
 import React from 'react';
 import PropTypes from 'prop-types';
+import ImmutablePureComponent from 'react-immutable-pure-component';
 import scheduleIdleTask from 'flavours/glitch/util/schedule_idle_task';
 import getRectFromEntry from 'flavours/glitch/util/get_rect_from_entry';
-import { is } from 'immutable';
 
-// Diff these props in the "rendered" state
-const updateOnPropsForRendered = ['id', 'index', 'listLength'];
-// Diff these props in the "unrendered" state
-const updateOnPropsForUnrendered = ['id', 'index', 'listLength', 'cachedHeight'];
-
-export default class IntersectionObserverArticle extends React.Component {
+export default class IntersectionObserverArticle extends ImmutablePureComponent {
 
   static propTypes = {
     intersectionObserverWrapper: PropTypes.object.isRequired,
@@ -27,15 +22,18 @@ export default class IntersectionObserverArticle extends React.Component {
   }
 
   shouldComponentUpdate (nextProps, nextState) {
-    const isUnrendered = !this.state.isIntersecting && (this.state.isHidden || this.props.cachedHeight);
-    const willBeUnrendered = !nextState.isIntersecting && (nextState.isHidden || nextProps.cachedHeight);
-    if (!!isUnrendered !== !!willBeUnrendered) {
-      // If we're going from rendered to unrendered (or vice versa) then update
+    if (!nextState.isIntersecting && nextState.isHidden) {
+      // It's only if we're not intersecting (i.e. offscreen) and isHidden is true
+      // that either "isIntersecting" or "isHidden" matter, and then they're
+      // the only things that matter (and updated ARIA attributes).
+      return this.state.isIntersecting || !this.state.isHidden || nextProps.listLength !== this.props.listLength;
+    } else if (nextState.isIntersecting && !this.state.isIntersecting) {
+      // If we're going from a non-intersecting state to an intersecting state,
+      // (i.e. offscreen to onscreen), then we definitely need to re-render
       return true;
     }
-    // Otherwise, diff based on props
-    const propsToDiff = isUnrendered ? updateOnPropsForUnrendered : updateOnPropsForRendered;
-    return !propsToDiff.every(prop => is(nextProps[prop], this.props[prop]));
+    // Otherwise, diff based on "updateOnProps" and "updateOnStates"
+    return super.shouldComponentUpdate(nextProps, nextState);
   }
 
   componentDidMount () {