From 5536ddba754fcdd65f8286c75829bf7860a393a5 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 8 Mar 2019 15:05:32 +0000
Subject: [PATCH 1/3] Make `prev_state` field optional

The `prev_state` field on events is not specced and so synapse shouldn't
explode if an event is missing the field.

Fixes #4787
---
 synapse/events/__init__.py |  1 -
 synapse/storage/events.py  | 15 ---------------
 2 files changed, 16 deletions(-)

diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index bd130f8816..fafa135182 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -141,7 +141,6 @@ class EventBase(object):
     origin = _event_dict_property("origin")
     origin_server_ts = _event_dict_property("origin_server_ts")
     prev_events = _event_dict_property("prev_events")
-    prev_state = _event_dict_property("prev_state")
     redacts = _event_dict_property("redacts")
     room_id = _event_dict_property("room_id")
     sender = _event_dict_property("sender")
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 990a5eaaae..428300ea0a 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -1407,21 +1407,6 @@ class EventsStore(StateGroupWorkerStore, EventFederationStore, EventsWorkerStore
             values=state_values,
         )
 
-        self._simple_insert_many_txn(
-            txn,
-            table="event_edges",
-            values=[
-                {
-                    "event_id": event.event_id,
-                    "prev_event_id": prev_id,
-                    "room_id": event.room_id,
-                    "is_state": True,
-                }
-                for event, _ in state_events_and_contexts
-                for prev_id, _ in event.prev_state
-            ],
-        )
-
         # Prefill the event cache
         self._add_to_cache(txn, events_and_contexts)
 

From cac4723afe9d805b5d2906665fafffaef5d3e1a9 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 8 Mar 2019 15:08:34 +0000
Subject: [PATCH 2/3] Newsfile

---
 changelog.d/4837.bugfix | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/4837.bugfix

diff --git a/changelog.d/4837.bugfix b/changelog.d/4837.bugfix
new file mode 100644
index 0000000000..989aeb82bb
--- /dev/null
+++ b/changelog.d/4837.bugfix
@@ -0,0 +1 @@
+Fix bug where synapse expected an un-specced `prev_state` field on state events.

From fe6c12e6cdbc2b34e93f6211c51e1eab33ae00c8 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 8 Mar 2019 16:38:23 +0000
Subject: [PATCH 3/3] Add comment to schema

---
 synapse/storage/schema/full_schemas/11/event_edges.sql | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/synapse/storage/schema/full_schemas/11/event_edges.sql b/synapse/storage/schema/full_schemas/11/event_edges.sql
index 52eec88357..bccd1c6f74 100644
--- a/synapse/storage/schema/full_schemas/11/event_edges.sql
+++ b/synapse/storage/schema/full_schemas/11/event_edges.sql
@@ -37,6 +37,8 @@ CREATE TABLE IF NOT EXISTS event_edges(
     event_id TEXT NOT NULL,
     prev_event_id TEXT NOT NULL,
     room_id TEXT NOT NULL,
+    -- We no longer insert prev_state into this table, so all new rows will have
+    -- is_state as false.
     is_state BOOL NOT NULL,
     UNIQUE (event_id, prev_event_id, room_id, is_state)
 );