From 2b03751c3cf0e64833afd36a1d393a5ce1d67e8d Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 25 May 2017 14:47:39 +0100
Subject: [PATCH] Don't return weird prev_group

---
 synapse/state.py | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/synapse/state.py b/synapse/state.py
index 536e2dc65..3f93f9e27 100644
--- a/synapse/state.py
+++ b/synapse/state.py
@@ -195,12 +195,12 @@ class StateHandler(object):
         Returns:
             synapse.events.snapshot.EventContext:
         """
-        context = EventContext()
 
         if event.internal_metadata.is_outlier():
             # If this is an outlier, then we know it shouldn't have any current
             # state. Certainly store.get_current_state won't return any, and
             # persisting the event won't store the state group.
+            context = EventContext()
             if old_state:
                 context.prev_state_ids = {
                     (s.type, s.state_key): s.event_id for s in old_state
@@ -219,6 +219,7 @@ class StateHandler(object):
             defer.returnValue(context)
 
         if old_state:
+            context = EventContext()
             context.prev_state_ids = {
                 (s.type, s.state_key): s.event_id for s in old_state
             }
@@ -245,6 +246,7 @@ class StateHandler(object):
 
         curr_state = entry.state
 
+        context = EventContext()
         context.prev_state_ids = curr_state
         if event.is_state():
             context.state_group = self.store.get_next_state_group()
@@ -257,11 +259,14 @@ class StateHandler(object):
             context.current_state_ids = dict(context.prev_state_ids)
             context.current_state_ids[key] = event.event_id
 
-            context.prev_group = entry.prev_group
-            context.delta_ids = entry.delta_ids
-            if context.delta_ids is not None:
-                context.delta_ids = dict(context.delta_ids)
-                context.delta_ids[key] = event.event_id
+            if entry.state_group:
+                context.prev_group = entry.state_group
+                context.delta_ids = {
+                    key: event.event_id
+                }
+            elif entry.prev_group:
+                context.prev_group = entry.prev_group
+                context.delta_ids = entry.delta_ids
         else:
             if entry.state_group is None:
                 entry.state_group = self.store.get_next_state_group()
@@ -305,8 +310,8 @@ class StateHandler(object):
             defer.returnValue(_StateCacheEntry(
                 state=state_list,
                 state_group=name,
-                prev_group=name,
-                delta_ids={},
+                prev_group=None,
+                delta_ids=None,
             ))
 
         with (yield self.resolve_linearizer.queue(group_names)):