From 4887ad092fd652fd831e842b22b4655087cf57b2 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 17 Dec 2019 13:08:18 +0000
Subject: [PATCH 1/3] Fix bug where we added duplicate event IDs as auth_events

---
 synapse/event_auth.py | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index d184b0273be1..9c2303e6e276 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import logging
+from typing import Set, Tuple
 
 from canonicaljson import encode_canonical_json
 from signedjson.key import decode_verify_key_bytes
@@ -637,7 +638,7 @@ def get_public_keys(invite_event):
     return public_keys
 
 
-def auth_types_for_event(event):
+def auth_types_for_event(event) -> Set[Tuple[str]]:
     """Given an event, return a list of (EventType, StateKey) that may be
     needed to auth the event. The returned list may be a superset of what
     would actually be required depending on the full state of the room.
@@ -646,20 +647,22 @@ def auth_types_for_event(event):
     actually auth the event.
     """
     if event.type == EventTypes.Create:
-        return []
+        return set()
 
-    auth_types = [
-        (EventTypes.PowerLevels, ""),
-        (EventTypes.Member, event.sender),
-        (EventTypes.Create, ""),
-    ]
+    auth_types = set(
+        (
+            (EventTypes.PowerLevels, ""),
+            (EventTypes.Member, event.sender),
+            (EventTypes.Create, ""),
+        )
+    )
 
     if event.type == EventTypes.Member:
         membership = event.content["membership"]
         if membership in [Membership.JOIN, Membership.INVITE]:
-            auth_types.append((EventTypes.JoinRules, ""))
+            auth_types.add((EventTypes.JoinRules, ""))
 
-        auth_types.append((EventTypes.Member, event.state_key))
+        auth_types.add((EventTypes.Member, event.state_key))
 
         if membership == Membership.INVITE:
             if "third_party_invite" in event.content:
@@ -667,6 +670,6 @@ def auth_types_for_event(event):
                     EventTypes.ThirdPartyInvite,
                     event.content["third_party_invite"]["signed"]["token"],
                 )
-                auth_types.append(key)
+                auth_types.add(key)
 
     return auth_types

From 599fc33cf3f7a45304aa38050fc0e9078af211a9 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 17 Dec 2019 13:12:12 +0000
Subject: [PATCH 2/3] Newsfile

---
 changelog.d/6560.bugfix | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/6560.bugfix

diff --git a/changelog.d/6560.bugfix b/changelog.d/6560.bugfix
new file mode 100644
index 000000000000..e75639f5b48a
--- /dev/null
+++ b/changelog.d/6560.bugfix
@@ -0,0 +1 @@
+Fix a cause of state resets in room versions 2 onwards.

From c0e0e5863d0ba017b0de607b3d3afbe4a179413c Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 17 Dec 2019 13:26:27 +0000
Subject: [PATCH 3/3] Use set literal

---
 synapse/event_auth.py | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 9c2303e6e276..350ed9351f19 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -649,13 +649,11 @@ def auth_types_for_event(event) -> Set[Tuple[str]]:
     if event.type == EventTypes.Create:
         return set()
 
-    auth_types = set(
-        (
-            (EventTypes.PowerLevels, ""),
-            (EventTypes.Member, event.sender),
-            (EventTypes.Create, ""),
-        )
-    )
+    auth_types = {
+        (EventTypes.PowerLevels, ""),
+        (EventTypes.Member, event.sender),
+        (EventTypes.Create, ""),
+    }
 
     if event.type == EventTypes.Member:
         membership = event.content["membership"]