Auto-scroll the left pane less frequently

ts/components/ContactPills.tsx

@@ -9,6 +9,7 @@ import React, {
   ReactNode,
 } from 'react';
 
+import { usePrevious } from '../util/hooks';
 import { scrollToBottom } from '../util/scrollToBottom';
 
 type PropsType = {
@@ -19,9 +20,7 @@ export const ContactPills: FunctionComponent<PropsType> = ({ children }) => {
   const elRef = useRef<null | HTMLDivElement>(null);
 
   const childCount = Children.count(children);
-  const previousChildCountRef = useRef<number>(childCount);
-  const previousChildCount = previousChildCountRef.current;
-  previousChildCountRef.current = childCount;
+  const previousChildCount = usePrevious(0, childCount);
 
   useEffect(() => {
     const hasAddedNewChild = childCount > previousChildCount;

ts/components/LeftPane.tsx

@@ -1,7 +1,7 @@
 // Copyright 2019-2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-import React, { useRef, useEffect, useMemo, CSSProperties } from 'react';
+import React, { useEffect, useMemo, CSSProperties } from 'react';
 import Measure, { MeasuredComponentProps } from 'react-measure';
 import { isNumber } from 'lodash';
 
@@ -37,6 +37,7 @@ import {
 
 import * as OS from '../OS';
 import { LocalizerType } from '../types/Util';
+import { usePrevious } from '../util/hooks';
 import { missingCaseError } from '../util/missingCaseError';
 
 import { ConversationList } from './ConversationList';
@@ -140,9 +141,10 @@ export const LeftPane: React.FC<PropsType> = ({
   startSettingGroupMetadata,
   toggleConversationInChooseMembers,
 }) => {
-  const previousModeSpecificPropsRef = useRef(modeSpecificProps);
-  const previousModeSpecificProps = previousModeSpecificPropsRef.current;
-  previousModeSpecificPropsRef.current = modeSpecificProps;
+  const previousModeSpecificProps = usePrevious(
+    modeSpecificProps,
+    modeSpecificProps
+  );
 
   // The left pane can be in various modes: the inbox, the archive, the composer, etc.
   //   Ideally, this would render subcomponents such as `<LeftPaneInbox>` or
@@ -331,6 +333,15 @@ export const LeftPane: React.FC<PropsType> = ({
 
   const getRow = useMemo(() => helper.getRow.bind(helper), [helper]);
 
+  const previousSelectedConversationId = usePrevious(
+    selectedConversationId,
+    selectedConversationId
+  );
+  const rowIndexToScrollTo: undefined | number =
+    previousSelectedConversationId === selectedConversationId
+      ? undefined
+      : helper.getRowIndexToScrollTo(selectedConversationId);
+
   // We ensure that the listKey differs between some modes (e.g. inbox/archived), ensuring
   //   that AutoSizer properly detects the new size of its slot in the flexbox. The
   //   archive explainer text at the top of the archive view causes problems otherwise.
@@ -403,9 +414,7 @@ export const LeftPane: React.FC<PropsType> = ({
                   }}
                   renderMessageSearchResult={renderMessageSearchResult}
                   rowCount={helper.getRowCount()}
-                  scrollToRowIndex={helper.getRowIndexToScrollTo(
-                    selectedConversationId
-                  )}
+                  scrollToRowIndex={rowIndexToScrollTo}
                   shouldRecomputeRowHeights={shouldRecomputeRowHeights}
                   showChooseGroupMembers={showChooseGroupMembers}
                   startNewConversationFromPhoneNumber={

ts/components/conversation/CallingNotification.tsx

@@ -1,7 +1,7 @@
-// Copyright 2020 Signal Messenger, LLC
+// Copyright 2020-2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-import React, { useState, useRef, useEffect } from 'react';
+import React, { useState, useEffect } from 'react';
 import Measure from 'react-measure';
 
 import { Timestamp } from './Timestamp';
@@ -11,6 +11,7 @@ import {
   CallingNotificationType,
   getCallingNotificationText,
 } from '../../util/callingNotification';
+import { usePrevious } from '../../util/hooks';
 import { missingCaseError } from '../../util/missingCaseError';
 import { Tooltip, TooltipPlacement } from '../Tooltip';
 
@@ -34,23 +35,18 @@ type PropsType = CallingNotificationType & PropsActionsType & PropsHousekeeping;
 export const CallingNotification: React.FC<PropsType> = React.memo(props => {
   const { conversationId, i18n, messageId, messageSizeChanged } = props;
 
-  const previousHeightRef = useRef<null | number>(null);
   const [height, setHeight] = useState<null | number>(null);
+  const previousHeight = usePrevious<null | number>(null, height);
 
   useEffect(() => {
     if (height === null) {
       return;
     }
 
-    if (
-      previousHeightRef.current !== null &&
-      height !== previousHeightRef.current
-    ) {
+    if (previousHeight !== null && height !== previousHeight) {
       messageSizeChanged(messageId, conversationId);
     }
-
-    previousHeightRef.current = height;
-  }, [height, conversationId, messageId, messageSizeChanged]);
+  }, [height, previousHeight, conversationId, messageId, messageSizeChanged]);
 
   let timestamp: number;
   let callType: 'audio' | 'video';

ts/util/hooks.ts

@@ -5,6 +5,13 @@ import * as React from 'react';
 import { ActionCreatorsMapObject, bindActionCreators } from 'redux';
 import { useDispatch } from 'react-redux';
 
+export function usePrevious<T>(initialValue: T, currentValue: T): T {
+  const previousValueRef = React.useRef<T>(initialValue);
+  const result = previousValueRef.current;
+  previousValueRef.current = currentValue;
+  return result;
+}
+
 // Restore focus on teardown
 export const useRestoreFocus = (
   // The ref for the element to receive initial focus

ts/util/lint/exceptions.json

@@ -14375,20 +14375,11 @@
     "rule": "React-useRef",
     "path": "ts/components/ContactPills.js",
     "line": "    const elRef = react_1.useRef(null);",
-    "lineNumber": 28,
+    "lineNumber": 29,
     "reasonCategory": "usageTrusted",
     "updated": "2021-03-01T18:34:36.638Z",
     "reasonDetail": "Used for scrolling. Doesn't otherwise manipulate the DOM"
   },
-  {
-    "rule": "React-useRef",
-    "path": "ts/components/ContactPills.js",
-    "line": "    const previousChildCountRef = react_1.useRef(childCount);",
-    "lineNumber": 30,
-    "reasonCategory": "usageTrusted",
-    "updated": "2021-03-01T18:34:36.638Z",
-    "reasonDetail": "Doesn't reference the DOM. Refers to a number"
-  },
   {
     "rule": "React-useRef",
     "path": "ts/components/ConversationList.js",
@@ -14495,24 +14486,6 @@
     "reasonCategory": "falseMatch",
     "updated": "2020-07-21T18:34:59.251Z"
   },
-  {
-    "rule": "React-useRef",
-    "path": "ts/components/LeftPane.js",
-    "line": "    const previousModeSpecificPropsRef = react_1.useRef(modeSpecificProps);",
-    "lineNumber": 52,
-    "reasonCategory": "usageTrusted",
-    "updated": "2021-02-12T16:25:08.285Z",
-    "reasonDetail": "Doesn't interact with the DOM."
-  },
-  {
-    "rule": "React-useRef",
-    "path": "ts/components/LeftPane.tsx",
-    "line": "  const previousModeSpecificPropsRef = useRef(modeSpecificProps);",
-    "lineNumber": 143,
-    "reasonCategory": "usageTrusted",
-    "updated": "2021-02-12T16:25:08.285Z",
-    "reasonDetail": "Doesn't interact with the DOM."
-  },
   {
     "rule": "React-createRef",
     "path": "ts/components/Lightbox.js",
@@ -14584,15 +14557,6 @@
     "updated": "2020-12-04T00:11:08.128Z",
     "reasonDetail": "Used to add (and remove) event listeners."
   },
-  {
-    "rule": "React-useRef",
-    "path": "ts/components/conversation/CallingNotification.js",
-    "line": "    const previousHeightRef = react_1.useRef(null);",
-    "lineNumber": 37,
-    "reasonCategory": "usageTrusted",
-    "updated": "2020-12-04T00:11:08.128Z",
-    "reasonDetail": "Doesn't interact with the DOM."
-  },
   {
     "rule": "React-useRef",
     "path": "ts/components/conversation/ContactModal.js",
@@ -15174,13 +15138,22 @@
     "reasonCategory": "falseMatch",
     "updated": "2020-09-08T23:07:22.682Z"
   },
+  {
+    "rule": "React-useRef",
+    "path": "ts/util/hooks.js",
+    "line": "    const previousValueRef = React.useRef(initialValue);",
+    "lineNumber": 29,
+    "reasonCategory": "usageTrusted",
+    "updated": "2021-03-18T21:41:28.361Z",
+    "reasonDetail": "A generic hook. Typically not to be used with non-DOM values."
+  },
   {
     "rule": "React-useRef",
     "path": "ts/util/hooks.js",
     "line": "    const unobserveRef = React.useRef(null);",
-    "lineNumber": 95,
+    "lineNumber": 102,
     "reasonCategory": "usageTrusted",
     "updated": "2021-01-08T15:46:32.143Z",
     "reasonDetail": "Doesn't manipulate the DOM. This is just a function."
   }
-]
+]