make sure we show display names & avatars on parts, and use the right type of content for displaynames for member events in general. fixes https://github.com/vector-im/vector-web/issues/1140 and https://github.com/vector-im/vector-web/issues/873 and a bunch more

lib/models/event.js

@@ -143,6 +143,8 @@ module.exports.MatrixEvent.prototype = {
     /**
      * Get either 'content' or 'prev_content' depending on if this event is
      * 'forward-looking' or not. This can be modified via event.forwardLooking.
+     * In practice, this means we get the chronologically earlier content value
+     * for this event (this method should surely be called getEarlierContent)
      * <strong>This method is experimental and may change.</strong>
      * @return {Object} event.content if this event is forward-looking, else
      * event.prev_content.

lib/models/room-member.js

@@ -203,7 +203,10 @@ RoomMember.prototype.getAvatarUrl =
 };
 
 function calculateDisplayName(member, event, roomState) {
-    var displayName = event.getDirectionalContent().displayname;
+    // N.B. getContent() not getDirectionalContent() at this point
+    // as we don't care about the chronologically earlier content
+    // but its current content!
+    var displayName = event.getContent().displayname;
     var selfUserId = member.userId;
 
     /*

lib/models/room-state.js

@@ -145,6 +145,19 @@ RoomState.prototype.setStateEvents = function(stateEvents) {
 
         if (event.getType() === "m.room.member") {
             var userId = event.getStateKey();
+
+            // leave events apparently elide the displayname or avatar_url,
+            // so let's fake one up so that we don't leak user ids
+            // into the timeline
+            if (event.getContent().membership === "leave" ||
+                event.getContent().membership === "ban")
+            {
+                event.getContent().avatar_url =
+                    event.getPrevContent().avatar_url;
+                event.getContent().displayname =
+                    event.getPrevContent().displayname;
+            }
+
             var member = self.members[userId];
             if (!member) {
                 member = new RoomMember(event.getRoomId(), userId);