From 79299891fd4c1afb20d1faa1bf397c14e353e942 Mon Sep 17 00:00:00 2001
From: David Baker <dbkr@users.noreply.github.com>
Date: Mon, 22 Jul 2024 15:24:49 +0200
Subject: [PATCH 1/2] Detect cycles when looking for predecessor rooms

---
 src/client.ts | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/client.ts b/src/client.ts
index 32ce1b26850..d7d4f08f16a 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -5401,10 +5401,15 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
 
     private findPredecessorRooms(room: Room, verifyLinks: boolean, msc3946ProcessDynamicPredecessor: boolean): Room[] {
         const ret: Room[] = [];
+        const seenRoomIDs = new Set<string>([room.roomId]);
 
         // Work backwards from newer to older rooms
         let predecessorRoomId = room.findPredecessor(msc3946ProcessDynamicPredecessor)?.roomId;
         while (predecessorRoomId !== null) {
+            if (predecessorRoomId) {
+                if (seenRoomIDs.has(predecessorRoomId)) return ret;
+                seenRoomIDs.add(predecessorRoomId);
+            }
             const predecessorRoom = this.getRoom(predecessorRoomId);
             if (predecessorRoom === null) {
                 break;

From e0ef467d7d2f223fde4d8203287779efd6425d03 Mon Sep 17 00:00:00 2001
From: David Baker <dbkr@users.noreply.github.com>
Date: Mon, 29 Jul 2024 13:55:08 +0100
Subject: [PATCH 2/2] break instead of return

---
 src/client.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/client.ts b/src/client.ts
index d7d4f08f16a..8e4609607ab 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -5407,7 +5407,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         let predecessorRoomId = room.findPredecessor(msc3946ProcessDynamicPredecessor)?.roomId;
         while (predecessorRoomId !== null) {
             if (predecessorRoomId) {
-                if (seenRoomIDs.has(predecessorRoomId)) return ret;
+                if (seenRoomIDs.has(predecessorRoomId)) break;
                 seenRoomIDs.add(predecessorRoomId);
             }
             const predecessorRoom = this.getRoom(predecessorRoomId);