Redacting membership events should immediately reset the displayname …

…& avatar of room members.

element-hq/element-ios#443

- Fix: The redacted state event was ignored in room state handling
- Add FIXME related to the blocker issue on server side SYN-724 ("prev_content is totally pruned by the server on redacted membership event").

MatrixSDK/Data/MXEventTimeline.m

@@ -569,10 +569,12 @@ - (void)handleRedaction:(MXEvent*)redactionEvent
     if (!redactedEvent || redactedEvent.isState)
     {
         // FIXME: Is @autoreleasepool block required or not here?
-        NSArray *stateEvents = _state.stateEvents;
+        NSMutableArray *stateEvents = [NSMutableArray arrayWithArray:_state.stateEvents];
 
-        for (MXEvent *stateEvent in stateEvents)
+        for (NSInteger index = 0; index < stateEvents.count; index++)
         {
+            MXEvent *stateEvent = stateEvents[index];
+
             if ([stateEvent.eventId isEqualToString:redactionEvent.redacts])
             {
                 NSLog(@"[MXEventTimeline] the current room state has been modified by the event redaction.");
@@ -581,6 +583,8 @@ - (void)handleRedaction:(MXEvent*)redactionEvent
                 redactedEvent = [stateEvent prune];
                 redactedEvent.redactedBecause = redactionEvent.JSONDictionary;
 
+                [stateEvents replaceObjectAtIndex:index withObject:redactedEvent];
+
                 // Reset the room state. //FIXME: is it possible to handle only the redacted event?
                 _state = [[MXRoomState alloc] initWithRoomId:room.roomId andMatrixSession:room.mxSession andDirection:YES];
                 [self initialiseState:stateEvents];

MatrixSDK/Data/MXRoomState.m

@@ -450,7 +450,8 @@ - (void)handleStateEvent:(MXEvent*)event
                     membersWithThirdPartyInviteTokenCache[roomMember.thirdPartyInviteToken] = roomMember;
                 }
             }
-            else
+            else// FIXME: In case of redacted membership event (prev_content is missing see SYN-724),
+                // the room member is then nil: the client considers by mistake the user is no more part of the room...
             {
                 // The user is no more part of the room. Remove him.
                 // This case happens during back pagination: we remove here users when they are not in the room yet.
@@ -550,13 +551,17 @@ - (NSString*)memberName:(NSString*)userId
 
         if (!member)
         {
-            // The user may not have joined the room yet. So try to resolve display name from presence data
-            // Note: This data may not be available
-            MXUser* user = [mxSession userWithUserId:userId];
-            if (user && user.displayname.length)
-            {
-                displayName = user.displayname;
-            }
+            // FIXME: In case of redacted membership event (prev_content is missing see SYN-724),
+            // the client considers by mistake that some users are no more part of the room.
+            // PATCH: we comment the following, else some redacted information re-appear spontaneously.
+
+//            // The user may not have joined the room yet. So try to resolve display name from presence data
+//            // Note: This data may not be available
+//            MXUser* user = [mxSession userWithUserId:userId];
+//            if (user && user.displayname.length)
+//            {
+//                displayName = user.displayname;
+//            }
         }
         else if (member.displayname.length)
         {