From bf3f8b8855c0723a65bdea61495b45d0fed24992 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Thu, 28 Feb 2019 17:46:22 +0000
Subject: [PATCH] Add more debug for #4422 (#4769)

---
 changelog.d/4769.misc    |  1 +
 synapse/handlers/sync.py | 11 +++++++++++
 2 files changed, 12 insertions(+)
 create mode 100644 changelog.d/4769.misc

diff --git a/changelog.d/4769.misc b/changelog.d/4769.misc
new file mode 100644
index 0000000000..89144b5425
--- /dev/null
+++ b/changelog.d/4769.misc
@@ -0,0 +1 @@
+Add more debug for #4422.
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index b4c4d89945..0e504f945d 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -1437,6 +1437,17 @@ class SyncHandler(object):
                     old_mem_ev = yield self.store.get_event(
                         old_mem_ev_id, allow_none=True
                     )
+
+                # debug for #4422
+                if has_join:
+                    prev_membership = None
+                    if old_mem_ev:
+                        prev_membership = old_mem_ev.membership
+                    logger.info(
+                        "Previous membership for room %s with join: %s (event %s)",
+                        room_id, prev_membership, old_mem_ev_id,
+                    )
+
                 if not old_mem_ev or old_mem_ev.membership != Membership.JOIN:
                     newly_joined_rooms.append(room_id)