Query the device lists of users when they are invited to a room.

Previously we only queried the device list when the user joined the room; now we
do it when they are invited too.  This means that new messages can be encrypted
for the devices of the invited user as of the point they were invited.

WARNING: This commit has two major problems however:
 1. If the invited user adds devices after being invited but before joining, the
    device-list will not be updated to the other servers in the room (as we don't
    know who those servers are).
 2. This introduces a regression, as previously the device-list would be correctly
    updated when when user joined the room.  However, this resync doesn't happen
    now, so devices which joined after the invite and before the join may never
    be added to the device-list.

This is being merged for DINSIC given the edge case of adding devices between
invite & join is pretty rare in their use case, but before it can be merged to
synapse in general we need to at least re-sync the devicelist when the user joins
or to implement some kind of pubsub mechanism to let interested servers subscribe
to devicelist updates on other servers irrespective of user join/invite membership.

This was originally #3484

synapse/handlers/sync.py

@@ -613,7 +613,7 @@ def generate_sync_result(self, sync_config, since_token=None, full_state=False):
         res = yield self._generate_sync_entry_for_rooms(
             sync_result_builder, account_data_by_room
         )
-        newly_joined_rooms, newly_joined_users, _, _ = res
+        newly_joined_rooms, newly_joined_or_invited_users, _, _ = res
         _, _, newly_left_rooms, newly_left_users = res
 
         block_all_presence_data = (
@@ -622,15 +622,15 @@ def generate_sync_result(self, sync_config, since_token=None, full_state=False):
         )
         if not block_all_presence_data:
             yield self._generate_sync_entry_for_presence(
-                sync_result_builder, newly_joined_rooms, newly_joined_users
+                sync_result_builder, newly_joined_rooms, newly_joined_or_invited_users
             )
 
         yield self._generate_sync_entry_for_to_device(sync_result_builder)
 
         device_lists = yield self._generate_sync_entry_for_device_list(
             sync_result_builder,
             newly_joined_rooms=newly_joined_rooms,
-            newly_joined_users=newly_joined_users,
+            newly_joined_or_invited_users=newly_joined_or_invited_users,
             newly_left_rooms=newly_left_rooms,
             newly_left_users=newly_left_users,
         )
@@ -706,7 +706,8 @@ def _generate_sync_entry_for_groups(self, sync_result_builder):
     @measure_func("_generate_sync_entry_for_device_list")
     @defer.inlineCallbacks
     def _generate_sync_entry_for_device_list(self, sync_result_builder,
-                                             newly_joined_rooms, newly_joined_users,
+                                             newly_joined_rooms,
+                                             newly_joined_or_invited_users,
                                              newly_left_rooms, newly_left_users):
         user_id = sync_result_builder.sync_config.user.to_string()
         since_token = sync_result_builder.since_token
@@ -720,15 +721,15 @@ def _generate_sync_entry_for_device_list(self, sync_result_builder,
             # share a room with?
             for room_id in newly_joined_rooms:
                 joined_users = yield self.state.get_current_user_in_room(room_id)
-                newly_joined_users.update(joined_users)
+                newly_joined_or_invited_users.update(joined_users)
 
             for room_id in newly_left_rooms:
                 left_users = yield self.state.get_current_user_in_room(room_id)
                 newly_left_users.update(left_users)
 
             # TODO: Check that these users are actually new, i.e. either they
             # weren't in the previous sync *or* they left and rejoined.
-            changed.update(newly_joined_users)
+            changed.update(newly_joined_or_invited_users)
 
             if not changed and not newly_left_users:
                 defer.returnValue(DeviceLists(
@@ -846,16 +847,17 @@ def _generate_sync_entry_for_account_data(self, sync_result_builder):
 
     @defer.inlineCallbacks
     def _generate_sync_entry_for_presence(self, sync_result_builder, newly_joined_rooms,
-                                          newly_joined_users):
+                                          newly_joined_or_invited_users):
         """Generates the presence portion of the sync response. Populates the
         `sync_result_builder` with the result.
 
         Args:
             sync_result_builder(SyncResultBuilder)
             newly_joined_rooms(list): List of rooms that the user has joined
                 since the last sync (or empty if an initial sync)
-            newly_joined_users(list): List of users that have joined rooms
-                since the last sync (or empty if an initial sync)
+            newly_joined_or_invited_users(list): List of users that have joined
+                or been invited to rooms since the last sync (or empty if an initial
+                sync)
         """
         now_token = sync_result_builder.now_token
         sync_config = sync_result_builder.sync_config
@@ -881,7 +883,7 @@ def _generate_sync_entry_for_presence(self, sync_result_builder, newly_joined_ro
             "presence_key", presence_key
         )
 
-        extra_users_ids = set(newly_joined_users)
+        extra_users_ids = set(newly_joined_or_invited_users)
         for room_id in newly_joined_rooms:
             users = yield self.state.get_current_user_in_room(room_id)
             extra_users_ids.update(users)
@@ -913,7 +915,8 @@ def _generate_sync_entry_for_rooms(self, sync_result_builder, account_data_by_ro
 
         Returns:
             Deferred(tuple): Returns a 4-tuple of
-            `(newly_joined_rooms, newly_joined_users, newly_left_rooms, newly_left_users)`
+            `(newly_joined_rooms, newly_joined_or_invited_users,
+            newly_left_rooms, newly_left_users)`
         """
         user_id = sync_result_builder.sync_config.user.to_string()
         block_all_room_ephemeral = (
@@ -984,8 +987,8 @@ def handle_room_entries(room_entry):
 
         sync_result_builder.invited.extend(invited)
 
-        # Now we want to get any newly joined users
-        newly_joined_users = set()
+        # Now we want to get any newly joined or invited users
+        newly_joined_or_invited_users = set()
         newly_left_users = set()
         if since_token:
             for joined_sync in sync_result_builder.joined:
@@ -994,19 +997,22 @@ def handle_room_entries(room_entry):
                 )
                 for event in it:
                     if event.type == EventTypes.Member:
-                        if event.membership == Membership.JOIN:
-                            newly_joined_users.add(event.state_key)
+                        if (
+                            event.membership == Membership.JOIN or
+                            event.membership == Membership.INVITE
+                        ):
+                            newly_joined_or_invited_users.add(event.state_key)
                         else:
                             prev_content = event.unsigned.get("prev_content", {})
                             prev_membership = prev_content.get("membership", None)
                             if prev_membership == Membership.JOIN:
                                 newly_left_users.add(event.state_key)
 
-        newly_left_users -= newly_joined_users
+        newly_left_users -= newly_joined_or_invited_users
 
         defer.returnValue((
             newly_joined_rooms,
-            newly_joined_users,
+            newly_joined_or_invited_users,
             newly_left_rooms,
             newly_left_users,
         ))
@@ -1051,7 +1057,7 @@ def _get_rooms_changed(self, sync_result_builder, ignored_users):
             where:
                 room_entries is a list [RoomSyncResultBuilder]
                 invited_rooms is a list [InvitedSyncResult]
-                newly_joined rooms is a list[str] of room ids
+                newly_joined_rooms is a list[str] of room ids
                 newly_left_rooms is a list[str] of room ids
         """
         user_id = sync_result_builder.sync_config.user.to_string()
@@ -1086,7 +1092,7 @@ def _get_rooms_changed(self, sync_result_builder, ignored_users):
             if room_id in sync_result_builder.joined_room_ids and non_joins:
                 # Always include if the user (re)joined the room, especially
                 # important so that device list changes are calculated correctly.
-                # If there are non join member events, but we are still in the room,
+                # If there are non-join member events, but we are still in the room,
                 # then the user must have left and joined
                 newly_joined_rooms.append(room_id)