Fix edge case thread summaries around events without a msgtype (#8576)

* Fix edge case thread summaries around events without a msgtype

* Remove incomprehensible comment

src/stores/room-list/MessagePreviewStore.ts

@@ -31,12 +31,16 @@ import { CallHangupEvent } from "./previews/CallHangupEvent";
 import { StickerEventPreview } from "./previews/StickerEventPreview";
 import { ReactionEventPreview } from "./previews/ReactionEventPreview";
 import { UPDATE_EVENT } from "../AsyncStore";
+import { IPreview } from "./previews/IPreview";
 
 // Emitted event for when a room's preview has changed. First argument will the room for which
 // the change happened.
 const ROOM_PREVIEW_CHANGED = "room_preview_changed";
 
-const PREVIEWS = {
+const PREVIEWS: Record<string, {
+    isState: boolean;
+    previewer: IPreview;
+}> = {
     'm.room.message': {
         isState: false,
         previewer: new MessageEventPreview(),
@@ -122,10 +126,7 @@ export class MessagePreviewStore extends AsyncStoreWithClient<IState> {
 
     public generatePreviewForEvent(event: MatrixEvent): string {
         const previewDef = PREVIEWS[event.getType()];
-        // TODO: Handle case where we don't have
-        if (!previewDef) return '';
-        const previewText = previewDef.previewer.getTextFor(event, null, true);
-        return previewText ?? '';
+        return previewDef?.previewer.getTextFor(event, null, true) ?? "";
     }
 
     private async generatePreview(room: Room, tagId?: TagID) {

src/stores/room-list/previews/IPreview.ts

@@ -26,7 +26,8 @@ export interface IPreview {
      * Gets the text which represents the event as a preview.
      * @param event The event to preview.
      * @param tagId Optional. The tag where the room the event was sent in resides.
+     * @param isThread Optional. Whether the preview being generated is for a thread summary.
      * @returns The preview.
      */
-    getTextFor(event: MatrixEvent, tagId?: TagID): string | null;
+    getTextFor(event: MatrixEvent, tagId?: TagID, isThread?: boolean): string | null;
 }

src/stores/room-list/previews/MessageEventPreview.ts

@@ -15,6 +15,7 @@ limitations under the License.
 */
 
 import { MatrixEvent } from "matrix-js-sdk/src/models/event";
+import { MsgType, RelationType } from "matrix-js-sdk/src/@types/event";
 
 import { IPreview } from "./IPreview";
 import { TagID } from "../models";
@@ -27,16 +28,17 @@ export class MessageEventPreview implements IPreview {
     public getTextFor(event: MatrixEvent, tagId?: TagID, isThread?: boolean): string {
         let eventContent = event.getContent();
 
-        if (event.isRelation("m.replace")) {
+        if (event.isRelation(RelationType.Replace)) {
             // It's an edit, generate the preview on the new text
             eventContent = event.getContent()['m.new_content'];
         }
 
-        if (!eventContent || !eventContent['body']) return null; // invalid for our purposes
+        if (!eventContent?.['body']) return null; // invalid for our purposes
 
-        let body = (eventContent['body'] || '').trim();
-        const msgtype = eventContent['msgtype'];
-        if (!body || !msgtype) return null; // invalid event, no preview
+        let body = eventContent['body'].trim();
+        if (!body) return null; // invalid event, no preview
+        // A msgtype is actually required in the spec but the app is a bit softer on this requirement
+        const msgtype = eventContent['msgtype'] ?? MsgType.Text;
 
         const hasHtml = eventContent.format === "org.matrix.custom.html" && eventContent.formatted_body;
         if (hasHtml) {
@@ -62,7 +64,7 @@ export class MessageEventPreview implements IPreview {
 
         body = sanitizeForTranslation(body);
 
-        if (msgtype === 'm.emote') {
+        if (msgtype === MsgType.Emote) {
             return _t("* %(senderName)s %(emote)s", { senderName: getSenderName(event), emote: body });
         }