handle sending relations to events that haven't been sent yet

src/matrix/room/sending/PendingEvent.js

@@ -16,6 +16,7 @@ limitations under the License.
 import {createEnum} from "../../../utils/enum.js";
 import {AbortError} from "../../../utils/error.js";
 import {REDACTION_TYPE} from "../common.js";
+import {getRelationFromContent} from "../timeline/relations.js";
 
 export const SendStatus = createEnum(
     "Waiting",
@@ -49,10 +50,23 @@ export class PendingEvent {
     get remoteId() { return this._data.remoteId; }
     get content() { return this._data.content; }
     get relatedTxnId() { return this._data.relatedTxnId; }
-    get relatedEventId() { return this._data.relatedEventId; }
+    get relatedEventId() {
+        const relation = getRelationFromContent(this.content);
+        if (relation) {
+            // may be null when target is not sent yet, is indented
+            return relation.event_id;
+        } else {
+            return this._data.relatedEventId;
+        }
+    }
 
     setRelatedEventId(eventId) {
-        this._data.relatedEventId = eventId;
+        const relation = getRelationFromContent(this.content);
+        if (relation) {
+            relation.event_id = eventId;
+        } else {
+            this._data.relatedEventId = eventId;
+        }
     }
 
     get data() { return this._data; }

src/matrix/room/sending/SendQueue.js

@@ -19,6 +19,7 @@ import {ConnectionError} from "../../error.js";
 import {PendingEvent, SendStatus} from "./PendingEvent.js";
 import {makeTxnId, isTxnId} from "../../common.js";
 import {REDACTION_TYPE} from "../common.js";
+import {getRelationFromContent} from "../timeline/relations.js";
 
 export class SendQueue {
     constructor({roomId, storage, hsApi, pendingEvents}) {
@@ -197,7 +198,13 @@ export class SendQueue {
     }
 
     async enqueueEvent(eventType, content, attachments, log) {
-        await this._enqueueEvent(eventType, content, attachments, null, null, log);
+        const relation = getRelationFromContent(content);
+        let relatedTxnId = null;
+        if (relation && isTxnId(relation.event_id)) {
+            relatedTxnId = relation.event_id;
+            relation.event_id = null;
+        }
+        await this._enqueueEvent(eventType, content, attachments, relatedTxnId, null, log);
     }
 
     async _enqueueEvent(eventType, content, attachments, relatedTxnId, relatedEventId, log) {

src/matrix/room/timeline/relations.js

@@ -41,7 +41,11 @@ export function getRelatedEventId(event) {
     return null;
 }
 
-export function getRelation(event) {
-	return event.content?.["m.relates_to"];
+export function getRelationFromContent(content) {
+    return content?.["m.relates_to"];
+}
+
+export function getRelation(event) {
+	return getRelationFromContent(event.content);
 }