Refactor the way we set outlier (#11634)

* `_auth_and_persist_outliers`: mark persisted events as outliers

Mark any events that get persisted via `_auth_and_persist_outliers` as, well,
outliers.

Currently this will be a no-op as everything will already be flagged as an
outlier, but I'm going to change that.

* `process_remote_join`: stop flagging as outlier

The events are now flagged as outliers later on, by `_auth_and_persist_outliers`.

* `send_join`: remove `outlier=True`

The events created here are returned in the result of `send_join` to
`FederationHandler.do_invite_join`. From there they are passed into
`FederationEventHandler.process_remote_join`, which passes them to
`_auth_and_persist_outliers`... which sets the `outlier` flag.

* `get_event_auth`: remove `outlier=True`

stop flagging the events returned by `get_event_auth` as outliers. This method
is only called by `_get_remote_auth_chain_for_event`, which passes the results
into `_auth_and_persist_outliers`, which will flag them as outliers.

* `_get_remote_auth_chain_for_event`: remove `outlier=True`

we pass all the events into `_auth_and_persist_outliers`, which will now flag
the events as outliers.

* `_check_sigs_and_hash_and_fetch`: remove unused `outlier` parameter

This param is now never set to True, so we can remove it.

* `_check_sigs_and_hash_and_fetch_one`: remove unused `outlier` param

This is no longer set anywhere, so we can remove it.

* `get_pdu`: remove unused `outlier` parameter

... and chase it down into `get_pdu_from_destination_raw`.

* `event_from_pdu_json`: remove redundant `outlier` param

This is never set to `True`, so can be removed.

* changelog

* update docstring

synapse/handlers/federation_event.py

@@ -421,9 +421,6 @@ class FederationEventHandler:
         Raises:
             SynapseError if the response is in some way invalid.
         """
-        for e in itertools.chain(auth_events, state):
-            e.internal_metadata.outlier = True
-
         event_map = {e.event_id: e for e in itertools.chain(auth_events, state)}
 
         create_event = None
@@ -1194,7 +1191,6 @@ class FederationEventHandler:
                         [destination],
                         event_id,
                         room_version,
-                        outlier=True,
                     )
                     if event is None:
                         logger.warning(
@@ -1223,9 +1219,10 @@ class FederationEventHandler:
         """Persist a batch of outlier events fetched from remote servers.
 
         We first sort the events to make sure that we process each event's auth_events
-        before the event itself, and then auth and persist them.
+        before the event itself.
 
-        Notifies about the events where appropriate.
+        We then mark the events as outliers, persist them to the database, and, where
+        appropriate (eg, an invite), awake the notifier.
 
         Params:
             room_id: the room that the events are meant to be in (though this has
@@ -1276,7 +1273,8 @@ class FederationEventHandler:
         Persists a batch of events where we have (theoretically) already persisted all
         of their auth events.
 
-        Notifies about the events where appropriate.
+        Marks the events as outliers, auths them, persists them to the database, and,
+        where appropriate (eg, an invite), awakes the notifier.
 
         Params:
             origin: where the events came from
@@ -1314,6 +1312,9 @@ class FederationEventHandler:
                         return None
                     auth.append(ae)
 
+                # we're not bothering about room state, so flag the event as an outlier.
+                event.internal_metadata.outlier = True
+
                 context = EventContext.for_outlier()
                 try:
                     validate_event_for_room_version(room_version_obj, event)