Handle state with input event as new events (#1415)

* SendEventWithState events as new

* Use cumulative state IDs for final event

* Error wrapping in calculateAndSetState

* Handle overwriting same event type and state key

* Hacky way to spot historical events

* Don't exclude from sync

* Don't generate output events when rewriting forward extremities

* Update output event check

* Historical output events

* Define output room event type

* Notify key changes on state

* Don't send our membership event twice

* Deduplicate state entries

* Tweaks

* Remove unnecessary nolint

* Fix current state upsert in sync API

* Send auth events as outliers, state events as rewrite

* Sync API don't consume state events

* Process events actually

* Improve outlier check

* Fix local room check

* Remove extra room check, it seems to break the whole damn world

* Fix federated join check

* Fix nil pointer exception

* Better comments on DeduplicateStateEntries

* Reflow forced federated joins

* Don't force federated join for possibly even local invites

* Comment SendEventWithState better

* Rewrite room state in sync API storage

* Add TODO

* Clean up all room data when receiving create event

* Don't generate output events for rewrites, but instead notify that state is rewritten on the final new event

* Rename to PurgeRoom

* Exclude backfilled messages from /sync

* Split out rewriting state from updating state from state res

Co-authored-by: Kegan Dougal <kegan@matrix.org>

roomserver/internal/perform/perform_join.go

@@ -183,33 +183,33 @@ func (r *Joiner) performJoinRoomByID(
 		return "", fmt.Errorf("eb.SetContent: %w", err)
 	}
 
-	// First work out if this is in response to an existing invite
-	// from a federated server. If it is then we avoid the situation
-	// where we might think we know about a room in the following
-	// section but don't know the latest state as all of our users
-	// have left.
+	// Force a federated join if we aren't in the room and we've been
+	// given some server names to try joining by.
 	serverInRoom, _ := helpers.IsServerCurrentlyInRoom(ctx, r.DB, r.ServerName, req.RoomIDOrAlias)
+	forceFederatedJoin := len(req.ServerNames) > 0 && !serverInRoom
+
+	// Force a federated join if we're dealing with a pending invite
+	// and we aren't in the room.
 	isInvitePending, inviteSender, _, err := helpers.IsInvitePending(ctx, r.DB, req.RoomIDOrAlias, req.UserID)
-	if err == nil && isInvitePending && !serverInRoom {
-		// Check if there's an invite pending.
+	if err == nil && isInvitePending {
 		_, inviterDomain, ierr := gomatrixserverlib.SplitID('@', inviteSender)
 		if ierr != nil {
 			return "", fmt.Errorf("gomatrixserverlib.SplitID: %w", err)
 		}
 
-		// Check that the domain isn't ours. If it's local then we don't
-		// need to do anything as our own copy of the room state will be
-		// up-to-date.
+		// If we were invited by someone from another server then we can
+		// assume they are in the room so we can join via them.
 		if inviterDomain != r.Cfg.Matrix.ServerName {
-			// Add the server of the person who invited us to the server list,
-			// as they should be a fairly good bet.
 			req.ServerNames = append(req.ServerNames, inviterDomain)
-
-			// Perform a federated room join.
-			return req.RoomIDOrAlias, r.performFederatedJoinRoomByID(ctx, req)
+			forceFederatedJoin = true
 		}
 	}
 
+	// If we should do a forced federated join then do that.
+	if forceFederatedJoin {
+		return req.RoomIDOrAlias, r.performFederatedJoinRoomByID(ctx, req)
+	}
+
 	// Try to construct an actual join event from the template.
 	// If this succeeds then it is a sign that the room already exists
 	// locally on the homeserver.