Ignore thread relations on state events for consistency with edits

spec/unit/models/event.spec.ts

@@ -308,4 +308,25 @@ describe("MatrixEvent", () => {
             });
         });
     });
+
+    it("should ignore thread relation on state events", async () => {
+        const stateEvent = new MatrixEvent({
+            event_id: "$event_id",
+            type: "some_state_event",
+            content: {
+                "foo": "bar",
+                "m.relates_to": {
+                    "event_id": "$thread_id",
+                    "m.in_reply_to": {
+                        event_id: "$thread_id",
+                    },
+                    "rel_type": "m.thread",
+                },
+            },
+            state_key: "",
+        });
+
+        expect(stateEvent.isState()).toBeTruthy();
+        expect(stateEvent.threadRootId).toBeUndefined();
+    });
 });

src/models/event.ts

@@ -34,7 +34,7 @@ import {
 import { Crypto } from "../crypto";
 import { deepSortedObjectEntries, internaliseString } from "../utils";
 import { RoomMember } from "./room-member";
-import { Thread, ThreadEvent, ThreadEventHandlerMap, THREAD_RELATION_TYPE } from "./thread";
+import { Thread, THREAD_RELATION_TYPE, ThreadEvent, ThreadEventHandlerMap } from "./thread";
 import { IActionsObject } from "../pushprocessor";
 import { TypedReEmitter } from "../ReEmitter";
 import { MatrixError } from "../http-api";
@@ -576,6 +576,10 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * Get the event ID of the thread head
      */
     public get threadRootId(): string | undefined {
+        // don't allow state events to be threaded as per the spec
+        if (this.isState()) {
+            return undefined;
+        }
         const relatesTo = this.getWireContent()?.["m.relates_to"];
         if (relatesTo?.rel_type === THREAD_RELATION_TYPE.name) {
             return relatesTo.event_id;
@@ -597,6 +601,11 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * A helper to check if an event is a thread's head or not
      */
     public get isThreadRoot(): boolean {
+        // don't allow state events to be threaded as per the spec
+        if (this.isState()) {
+            return false;
+        }
+
         const threadDetails = this.getServerAggregatedRelation<IThreadBundledRelationship>(THREAD_RELATION_TYPE.name);
 
         // Bundled relationships only returned when the sync response is limited
@@ -1365,7 +1374,11 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
         // Relation info is lifted out of the encrypted content when sent to
         // encrypted rooms, so we have to check `getWireContent` for this.
         const relation = this.getWireContent()?.["m.relates_to"];
-        if (this.isState() && relation?.rel_type === RelationType.Replace) {
+        if (
+            this.isState() &&
+            relation?.rel_type &&
+            ([RelationType.Replace, RelationType.Thread] as string[]).includes(relation.rel_type)
+        ) {
             // State events cannot be m.replace relations
             return false;
         }
@@ -1618,6 +1631,10 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * @param thread - the thread
      */
     public setThread(thread?: Thread): void {
+        // don't allow state events to be threaded as per the spec
+        if (this.isState()) {
+            return;
+        }
         if (this.thread) {
             this.reEmitter.stopReEmitting(this.thread, [ThreadEvent.Update]);
         }