Adjust fetchEditsWhereNeeded to use a clearer filter and async functi…

…on (matrix-org#3411)

* Make a clear and explicit filter on which events are considered for fetchEventsWhereNeeded

* Convert the logic in fetchEventsWhereNeeded to an async function

src/models/thread.ts

@@ -519,26 +519,26 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
         const recursionSupport = this.client.canSupport.get(Feature.RelationsRecursion) ?? ServerSupport.Unsupported;
         if (recursionSupport === ServerSupport.Unsupported) {
             return Promise.all(
-                events
-                    .filter((e) => e.isEncrypted())
-                    .map((event: MatrixEvent) => {
-                        // 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(), {
+                events.filter(isAnEncryptedThreadMessage).map(async (event: MatrixEvent) => {
+                    try {
+                        const relations = await this.client.relations(
+                            this.roomId,
+                            event.getId()!,
+                            RelationType.Replace,
+                            event.getType(),
+                            {
                                 limit: 1,
-                            })
-                            .then((relations) => {
-                                if (relations.events.length) {
-                                    const editEvent = relations.events[0];
-                                    event.makeReplaced(editEvent);
-                                    this.insertEventIntoTimeline(editEvent);
-                                }
-                            })
-                            .catch((e) => {
-                                logger.error("Failed to load edits for encrypted thread event", e);
-                            });
-                    }),
+                            },
+                        );
+                        if (relations.events.length) {
+                            const editEvent = relations.events[0];
+                            event.makeReplaced(editEvent);
+                            this.insertEventIntoTimeline(editEvent);
+                        }
+                    } catch (e) {
+                        logger.error("Failed to load edits for encrypted thread event", e);
+                    }
+                }),
             );
         }
     }
@@ -708,6 +708,16 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
     }
 }
 
+/**
+ * Decide whether an event deserves to have its potential edits fetched.
+ *
+ * @returns true if this event is encrypted and is a message that is part of a
+ * thread - either inside it, or a root.
+ */
+function isAnEncryptedThreadMessage(event: MatrixEvent): boolean {
+    return event.isEncrypted() && (event.isRelation(THREAD_RELATION_TYPE.name) || event.isThreadRoot);
+}
+
 export const FILTER_RELATED_BY_SENDERS = new ServerControlledNamespacedValue(
     "related_by_senders",
     "io.element.relation_senders",