From a1c5c1b997298b1662a3424bb5a4ddd000fa5a5b Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Thu, 12 May 2022 12:43:55 +0100
Subject: [PATCH] Remove duplicates

---
 roomserver/internal/input/input_latest_events.go |  6 ++++--
 roomserver/types/types.go                        | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/roomserver/internal/input/input_latest_events.go b/roomserver/internal/input/input_latest_events.go
index c9d2a4785..b03cceed6 100644
--- a/roomserver/internal/input/input_latest_events.go
+++ b/roomserver/internal/input/input_latest_events.go
@@ -236,8 +236,10 @@ func (u *latestEventsUpdater) latestState() error {
 	// Get a list of the current latest events. This may or may not
 	// include the new event from the input path, depending on whether
 	// it is a forward extremity or not.
-	latestStateAtEvents := make([]types.StateAtEvent, len(u.latest))
-	for i := range append(u.latest, u.oldLatest...) {
+	combinedExtremities := types.StateAtEventAndReferences(append(u.latest, u.oldLatest...))
+	util.Unique(combinedExtremities)
+	latestStateAtEvents := make([]types.StateAtEvent, len(combinedExtremities))
+	for i := range combinedExtremities {
 		latestStateAtEvents[i] = u.latest[i].StateAtEvent
 	}
 
diff --git a/roomserver/types/types.go b/roomserver/types/types.go
index 65fbee04e..ce4e5fd1e 100644
--- a/roomserver/types/types.go
+++ b/roomserver/types/types.go
@@ -18,6 +18,7 @@ package types
 import (
 	"encoding/json"
 	"sort"
+	"strings"
 
 	"github.com/matrix-org/gomatrixserverlib"
 	"golang.org/x/crypto/blake2b"
@@ -166,6 +167,20 @@ type StateAtEventAndReference struct {
 	gomatrixserverlib.EventReference
 }
 
+type StateAtEventAndReferences []StateAtEventAndReference
+
+func (s StateAtEventAndReferences) Less(a, b int) bool {
+	return strings.Compare(s[a].EventID, s[b].EventID) < 0
+}
+
+func (s StateAtEventAndReferences) Len() int {
+	return len(s)
+}
+
+func (s StateAtEventAndReferences) Swap(a, b int) {
+	s[a], s[b] = s[b], s[a]
+}
+
 // An Event is a gomatrixserverlib.Event with the numeric event ID attached.
 // It is when performing bulk event lookup in the database.
 type Event struct {