From 415a869f1f53bd4bf22a69e74081875dc9c17735 Mon Sep 17 00:00:00 2001
From: Jason Little <j.little@famedly.com>
Date: Mon, 3 Aug 2026 13:47:26 -0500
Subject: [PATCH] fix RemoteJoinHelper to handle v12 rooms (#20021)

While preparing for the default room version change to "12", the new
tests for
[FederationJoinUpgradedRoomTestCase](https://github.com/element-hq/synapse/blob/36664cac4fdec38993c68078cd9a82452b56dca7/tests/federation/test_federation_join_upgraded_room.py#L44)
were unable to handle creation events inside of the manufactured
`auth_events` sections. All of these tests fail.

Related to https://github.com/element-hq/synapse/pull/20015 as another
recent fix to `RemoteJoinHelper`


### Testing strategy

To test, I recommend changing the `DEFAULT_ROOM_VERSION` in [the
`server.py` config
file](https://github.com/element-hq/synapse/blob/36664cac4fdec38993c68078cd9a82452b56dca7/synapse/config/server.py#L179)
to `"12"`, then running `poetry run trial
tests.federation.test_federation_join_upgraded_room.FederationJoinUpgradedRoomTestCase`
for these selective tests. Alternatively, creating the
`default_config()` for the `TestCase` in question to set the default
room version, but that is more work.
---
 changelog.d/20021.misc           |  1 +
 tests/federation/_remote_join.py | 16 ++++++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)
 create mode 100644 changelog.d/20021.misc

diff --git a/changelog.d/20021.misc b/changelog.d/20021.misc
new file mode 100644
index 0000000000..9291f5eea0
--- /dev/null
+++ b/changelog.d/20021.misc
@@ -0,0 +1 @@
+Fix `RemoteJoinHelper` test helper to handle room version "12" rooms. Contributed by @famedly @jason-famedly.
diff --git a/tests/federation/_remote_join.py b/tests/federation/_remote_join.py
index feb9c528c9..8a4e438466 100644
--- a/tests/federation/_remote_join.py
+++ b/tests/federation/_remote_join.py
@@ -146,7 +146,9 @@ class RemoteJoinHelper:
                     "type": EventTypes.Member,
                     "state_key": remote_creator_user_id,
                     "content": {"membership": Membership.JOIN},
-                    "auth_events": [room_create_event.event_id],
+                    "auth_events": [room_create_event.event_id]
+                    if not room_version.msc4291_room_ids_as_hashes
+                    else [],
                     "prev_events": [room_create_event.event_id],
                 },
                 room_version=room_version,
@@ -173,7 +175,9 @@ class RemoteJoinHelper:
                         "auth_events": [
                             room_create_event.event_id,
                             creator_membership_event.event_id,
-                        ],
+                        ]
+                        if not room_version.msc4291_room_ids_as_hashes
+                        else [creator_membership_event.event_id],
                         "prev_events": [prev_event.event_id],
                     },
                     room_version=room_version,
@@ -215,7 +219,9 @@ class RemoteJoinHelper:
                     "auth_events": [
                         room_create_event.event_id,
                         creator_membership_event.event_id,
-                    ],
+                    ]
+                    if not room_version.msc4291_room_ids_as_hashes
+                    else [creator_membership_event.event_id],
                     "prev_events": [
                         extra_events[-1].event_id
                         if extra_events
@@ -254,7 +260,9 @@ class RemoteJoinHelper:
                 "auth_events": [
                     room_create_event.event_id,
                     invite_membership_event.event_id,
-                ],
+                ]
+                if not room_version.msc4291_room_ids_as_hashes
+                else [invite_membership_event.event_id],
                 "prev_events": [invite_membership_event.event_id],
             },
             room_version=room_version,