Test inserting edit events into the thread timeline "on demand" (#3410)

* Fix an existing test for editing messages in threads

While attempting to test a new change, I discovered that the test
"should allow edits to be added to thread timeline" did not actually
fail if its assertions failed. Further, those assertions were incorrect.

So this change fixes the test to create the thread, wait for it to be
initialised, and then add events to it. This simplifies the flow and
ensures the test fails if something unexpected happens.

* Move editing test into thread.spec.ts

* Isolate Thread global modification in beforeAll()

* Delete unneeded setUnsigned call

* Use standard message-creation methods

* Rename event variables

* Rename sender->user

* Remove unneeded variables

* Extract distractions into functions

* Fetch edits for thread messages

Modifies fetchEditsWhereNeeded to allow edits of threaded messages. The
code before prevented any relations from fetching edits, but of course
events in threads are relations.

We definitely want thread messages to get their edits fetched, and I
assume this is working in the real code, probably because the event
being looked at is some kind of eventmapped thing that doesn't have
proper relations visible on it.

In tests, if we don't make this change, we can't see edits getting
fetched.

* Add a test for fetching edits on demand in a thread

This test demonstrates the current behaviour, which contains a bug - we
don't actually add the right event to the timeline.

spec/unit/models/thread.spec.ts

@@ -22,7 +22,7 @@ import { Thread, THREAD_RELATION_TYPE, ThreadEvent, FeatureSupport } from "../..
 import { makeThreadEvent, mkThread } from "../../test-utils/thread";
 import { TestClient } from "../../TestClient";
 import { emitPromise, mkEdit, mkMessage, mkReaction, mock } from "../../test-utils/test-utils";
-import { Direction, EventStatus, MatrixEvent } from "../../../src";
+import { Direction, EventStatus, EventType, MatrixEvent } from "../../../src";
 import { ReceiptType } from "../../../src/@types/read_receipts";
 import { getMockClientWithEventEmitter, mockClientMethodsUser } from "../../test-utils/client";
 import { ReEmitter } from "../../../src/ReEmitter";
@@ -615,7 +615,7 @@ describe("Thread", () => {
                 Thread.hasServerSideSupport = previousThreadHasServerSideSupport;
             });
 
-            it("should allow edits to be added to thread timeline", async () => {
+            it("Adds edits from sync to the thread timeline and applies them", async () => {
                 // Given a thread
                 const client = createClient();
                 const user = "@alice:matrix.org";
@@ -637,6 +637,45 @@ describe("Thread", () => {
                 // And the first message has been edited
                 expect(secondLastEvent.getContent().body).toEqual("edit");
             });
+
+            it("Adds edits fetched on demand to the thread timeline and applies them", async () => {
+                // Given we don't support recursive relations
+                const client = createClient(new Map([[Feature.RelationsRecursion, ServerSupport.Unsupported]]));
+                // And we have a thread
+                const user = "@alice:matrix.org";
+                const room = "!room:z";
+                const thread = await createThread(client, user, room);
+
+                // When a message is added to the thread, and an edit to it is provided on demand
+                const messageToEdit = createThreadMessage(thread.id, user, room, "Thread reply");
+                // (fetchEditsWhereNeeded only applies to encrypted messages for some reason)
+                messageToEdit.event.type = EventType.RoomMessageEncrypted;
+                const editEvent = mkEdit(messageToEdit, client, user, room, "edit");
+                mocked(client.relations).mockImplementation(async (_roomId, eventId) => {
+                    if (eventId === messageToEdit.getId()) {
+                        return { events: [editEvent] };
+                    } else {
+                        return { events: [] };
+                    }
+                });
+                await thread.addEvent(messageToEdit, false);
+
+                // THIS IS THE CORRECT BEHAVIOUR
+                // Then both events end up in the timeline
+                //const lastEvent = thread.timeline.at(-1)!;
+                //const secondLastEvent = thread.timeline.at(-2)!;
+                //expect(lastEvent).toBe(editEvent);
+                //expect(secondLastEvent).toBe(messageToEdit);
+
+                //// And the first message has been edited
+                //expect(secondLastEvent.getContent().body).toEqual("edit");
+
+                // TODO: For now, we incorrecly DON'T add the event to the timeline
+                const lastEvent = thread.timeline.at(-1)!;
+                expect(lastEvent).toBe(messageToEdit);
+                // But the original is edited, as expected
+                expect(lastEvent.getContent().body).toEqual("edit");
+            });
         });
     });
 });
@@ -661,8 +700,10 @@ function createThreadMessage(threadId: string, user: string, room: string, msg:
  */
 async function createThread(client: MatrixClient, user: string, roomId: string): Promise<Thread> {
     const root = mkMessage({ event: true, user, room: roomId, msg: "Thread root" });
-
     const room = new Room(roomId, client, "@roomcreator:x");
+
+    // Ensure the root is in the room timeline
+    root.setThreadId(root.getId());
     room.addLiveEvents([root]);
 
     // Create the thread and wait for it to be initialised
@@ -676,10 +717,10 @@ async function createThread(client: MatrixClient, user: string, roomId: string):
  * Create a MatrixClient that supports threads and has all the methods used when
  * creating a thread that call out to HTTP endpoints mocked out.
  */
-function createClient(): MatrixClient {
+function createClient(canSupport = new Map()): MatrixClient {
     const client = mock(MatrixClient, "MatrixClient");
     client.reEmitter = mock(ReEmitter, "ReEmitter");
-    client.canSupport = new Map();
+    client.canSupport = canSupport;
 
     jest.spyOn(client, "supportsThreads").mockReturnValue(true);
     jest.spyOn(client, "getEventMapper").mockReturnValue(eventMapperFor(client, {}));

src/models/thread.ts

@@ -522,7 +522,8 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
                 events
                     .filter((e) => e.isEncrypted())
                     .map((event: MatrixEvent) => {
-                        if (event.isRelation()) return; // skip - relations don't get edits
+                        // The only type of relation that gets edits is a thread message.
+                        if (event.getThread() === undefined && event.isRelation()) return;
                         return this.client
                             .relations(this.roomId, event.getId()!, RelationType.Replace, event.getType(), {
                                 limit: 1,