Centralise display alias getters

src/Rooms.ts

@@ -28,7 +28,15 @@ import { MatrixClientPeg } from './MatrixClientPeg';
  * @returns {string} A display alias for the given room
  */
 export function getDisplayAliasForRoom(room: Room): string {
-    return room.getCanonicalAlias() || room.getAltAliases()[0];
+    return getDisplayAliasForAliasSet(
+        room.getCanonicalAlias(), room.getAltAliases(),
+    );
+}
+
+// The various display alias getters all feed through this one path so there's a
+// single place to change the logic.
+export function getDisplayAliasForAliasSet(canonicalAlias: string, altAliases: string[]): string {
+    return canonicalAlias || altAliases?.[0];
 }
 
 export function looksLikeDirectMessageRoom(room: Room, myUserId: string): boolean {

src/components/structures/RoomDirectory.tsx

@@ -44,6 +44,7 @@ import NetworkDropdown from "../views/directory/NetworkDropdown";
 import ScrollPanel from "./ScrollPanel";
 import Spinner from "../views/elements/Spinner";
 import { ActionPayload } from "../../dispatcher/payloads";
+import { getDisplayAliasForAliasSet } from "../../Rooms";
 
 const MAX_NAME_LENGTH = 80;
 const MAX_TOPIC_LENGTH = 800;
@@ -854,5 +855,5 @@ export default class RoomDirectory extends React.Component<IProps, IState> {
 // Similar to matrix-react-sdk's MatrixTools.getDisplayAliasForRoom
 // but works with the objects we get from the public room list
 function getDisplayAliasForRoom(room: IRoom) {
-    return room.canonical_alias || room.aliases?.[0] || "";
+    return getDisplayAliasForAliasSet(room.canonical_alias, room.aliases);
 }

src/components/structures/SpaceRoomDirectory.tsx

@@ -42,6 +42,7 @@ import { useStateToggle } from "../../hooks/useStateToggle";
 import { getChildOrder } from "../../stores/SpaceStore";
 import AccessibleTooltipButton from "../views/elements/AccessibleTooltipButton";
 import { linkifyElement } from "../../HtmlUtils";
+import { getDisplayAliasForAliasSet } from "../../Rooms";
 
 interface IHierarchyProps {
     space: Room;
@@ -666,5 +667,5 @@ export default SpaceRoomDirectory;
 // Similar to matrix-react-sdk's MatrixTools.getDisplayAliasForRoom
 // but works with the objects we get from the public room list
 function getDisplayAliasForRoom(room: ISpaceSummaryRoom) {
-    return room.canonical_alias || (room.aliases ? room.aliases[0] : "");
+    return getDisplayAliasForAliasSet(room.canonical_alias, room.aliases);
 }

src/components/views/rooms/RoomDetailRow.js

@@ -1,5 +1,5 @@
 /*
-Copyright 2017 New Vector Ltd.
+Copyright 2017-2021 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -21,9 +21,10 @@ import { linkifyElement } from '../../../HtmlUtils';
 import PropTypes from 'prop-types';
 import { replaceableComponent } from "../../../utils/replaceableComponent";
 import { mediaFromMxc } from "../../../customisations/Media";
+import { getDisplayAliasForAliasSet } from '../../../Rooms';
 
 export function getDisplayAliasForRoom(room) {
-    return room.canonicalAlias || (room.aliases ? room.aliases[0] : "");
+    return getDisplayAliasForAliasSet(room.canonicalAlias, room.aliases);
 }
 
 export const roomShape = PropTypes.shape({