From 08c5181a8dfcc3977c422797b876bcfddf75ab4f Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Thu, 9 Jul 2020 12:48:15 +0100
Subject: [PATCH] Fix `can only concatenate list (not "tuple") to list`
 exception (#7810)

It seems auth_events can be either a list or a tuple, depending on Things.
---
 changelog.d/7810.bugfix         | 1 +
 synapse/handlers/room_member.py | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/7810.bugfix

diff --git a/changelog.d/7810.bugfix b/changelog.d/7810.bugfix
new file mode 100644
index 000000000000..2772eeb0db89
--- /dev/null
+++ b/changelog.d/7810.bugfix
@@ -0,0 +1 @@
+Fix 'stuck invites' which happen when we are unable to reject a room invite received over federation.
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 178d7db94e3b..41adaf3bf374 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -1072,7 +1072,7 @@ async def _locally_reject_invite(
             alg, h = compute_event_reference_hash(invite_event)
             invite_hash = (invite_event.event_id, {alg: encode_base64(h)})
 
-        auth_events = invite_event.auth_events + (invite_hash,)
+        auth_events = tuple(invite_event.auth_events) + (invite_hash,)
         prev_events = (invite_hash,)
 
         # we cap depth of generated events, to ensure that they are not