Let users see their own leave events

... otherwise clients get confused.

Fixes https://matrix.org/jira/browse/SYN-662,
element-hq/element-web#368

synapse/handlers/_base.py

@@ -37,6 +37,15 @@
 )
 
 
+MEMBERSHIP_PRIORITY = (
+    Membership.JOIN,
+    Membership.INVITE,
+    Membership.KNOCK,
+    Membership.LEAVE,
+    Membership.BAN,
+)
+
+
 class BaseHandler(object):
     """
     Common base class for the event handlers.
@@ -72,6 +81,7 @@ def filter_events_for_clients(self, user_tuples, events, event_id_to_state):
                 * the user is not currently a member of the room, and:
                 * the user has not been a member of the room since the
                 given events
+            events ([synapse.events.EventBase]): list of events to filter
         """
         forgotten = yield defer.gatherResults([
             self.store.who_forgot_in_room(
@@ -86,6 +96,12 @@ def filter_events_for_clients(self, user_tuples, events, event_id_to_state):
         )
 
         def allowed(event, user_id, is_peeking):
+            """
+            Args:
+                event (synapse.events.EventBase): event to check
+                user_id (str)
+                is_peeking (bool)
+            """
             state = event_id_to_state[event.event_id]
 
             # get the room_visibility at the time of the event.
@@ -117,17 +133,30 @@ def allowed(event, user_id, is_peeking):
                 if old_priority < new_priority:
                     visibility = prev_visibility
 
-            # get the user's membership at the time of the event. (or rather,
-            # just *after* the event. Which means that people can see their
-            # own join events, but not (currently) their own leave events.)
-            membership_event = state.get((EventTypes.Member, user_id), None)
-            if membership_event:
-                if membership_event.event_id in event_id_forgotten:
-                    membership = None
-                else:
-                    membership = membership_event.membership
-            else:
-                membership = None
+            # likewise, if the event is the user's own membership event, use
+            # the 'most joined' membership
+            membership = None
+            if event.type == EventTypes.Member and event.state_key == user_id:
+                membership = event.content.get("membership", None)
+                if membership not in MEMBERSHIP_PRIORITY:
+                    membership = "leave"
+
+                prev_content = event.unsigned.get("prev_content", {})
+                prev_membership = prev_content.get("membership", None)
+                if prev_membership not in MEMBERSHIP_PRIORITY:
+                    prev_membership = "leave"
+
+                new_priority = MEMBERSHIP_PRIORITY.index(membership)
+                old_priority = MEMBERSHIP_PRIORITY.index(prev_membership)
+                if old_priority < new_priority:
+                    membership = prev_membership
+
+            # otherwise, get the user's membership at the time of the event.
+            if membership is None:
+                membership_event = state.get((EventTypes.Member, user_id), None)
+                if membership_event:
+                    if membership_event.event_id not in event_id_forgotten:
+                        membership = membership_event.membership
 
             # if the user was a member of the room at the time of the event,
             # they can see it.