From 65c68015a20faaabd5e496ffb80d8af767f16d1d Mon Sep 17 00:00:00 2001
From: Michael Telatynski <7t3chguy@gmail.com>
Date: Wed, 20 Apr 2022 08:52:23 +0100
Subject: [PATCH 1/3] Ignore m.replace relations on state events, they're
 invalid

---
 src/models/event.ts | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/models/event.ts b/src/models/event.ts
index f28176b94f0..e65aa7b053c 100644
--- a/src/models/event.ts
+++ b/src/models/event.ts
@@ -1336,6 +1336,10 @@ export class MatrixEvent extends TypedEventEmitter<EmittedEvents, MatrixEventHan
         if (this.isRedacted() && newEvent) {
             return;
         }
+        // don't allow state events to be replaced using this mechanism as per MSC2676
+        if (this.isState()) {
+            return;
+        }
         if (this._replacingEvent !== newEvent) {
             this._replacingEvent = newEvent;
             this.emit(MatrixEventEvent.Replaced, this);

From de5c343597fc934a008dfa31842f7a2c5600a271 Mon Sep 17 00:00:00 2001
From: Michael Telatynski <7t3chguy@gmail.com>
Date: Wed, 20 Apr 2022 09:31:23 +0100
Subject: [PATCH 2/3] Add tests

---
 spec/unit/relations.spec.ts | 49 +++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/spec/unit/relations.spec.ts b/spec/unit/relations.spec.ts
index 1b479ebbef8..7e08f7491b0 100644
--- a/spec/unit/relations.spec.ts
+++ b/spec/unit/relations.spec.ts
@@ -130,4 +130,53 @@ describe("Relations", function() {
             await relationsCreated;
         }
     });
+
+    it("edits shouldn't apply to state events", async () => {
+        const userId = "@bob:example.com";
+        const room = new Room("room123", null, userId);
+        const relations = new Relations("m.replace", "m.room.topic", room);
+
+        // Create an instance of a state event with rel_type m.replace
+        const originalTopic = new MatrixEvent({
+            "sender": userId,
+            "type": "m.room.topic",
+            "event_id": "$orig",
+            "room_id": room.roomId,
+            "content": {
+                "topic": "orig",
+            },
+        });
+        const badlyEditedTopic = new MatrixEvent({
+            "sender": userId,
+            "type": "m.room.topic",
+            "event_id": "$orig",
+            "room_id": room.roomId,
+            "content": {
+                "topic": "topic",
+                "m.new_content": {
+                    "topic": "edit",
+                },
+                "m.relates_to": {
+                    "event_id": "$orig",
+                    "rel_type": "m.replace",
+                },
+            },
+        });
+
+        // Add the original topic and check results
+        {
+            relations.addEvent(originalTopic);
+            expect(originalTopic.replacingEvent()).toBe(null);
+            expect(originalTopic.getContent().topic).toBe("orig");
+        }
+
+        // Add the badly edited topic and check results
+        {
+            relations.addEvent(badlyEditedTopic);
+            expect(originalTopic.replacingEvent()).toBe(null);
+            expect(originalTopic.getContent().topic).toBe("orig");
+            expect(badlyEditedTopic.replacingEvent()).toBe(null);
+            expect(badlyEditedTopic.getContent().topic).toBe("topic");
+        }
+    });
 });

From d23ae9fc82f5dfccf166e614dac5d91b39b13fb8 Mon Sep 17 00:00:00 2001
From: Michael Telatynski <7t3chguy@gmail.com>
Date: Wed, 20 Apr 2022 09:34:28 +0100
Subject: [PATCH 3/3] Fix test

---
 spec/unit/relations.spec.ts | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/spec/unit/relations.spec.ts b/spec/unit/relations.spec.ts
index 7e08f7491b0..2472bd8f688 100644
--- a/spec/unit/relations.spec.ts
+++ b/spec/unit/relations.spec.ts
@@ -131,7 +131,7 @@ describe("Relations", function() {
         }
     });
 
-    it("edits shouldn't apply to state events", async () => {
+    it("should ignore m.replace for state events", async () => {
         const userId = "@bob:example.com";
         const room = new Room("room123", null, userId);
         const relations = new Relations("m.replace", "m.room.topic", room);
@@ -145,6 +145,7 @@ describe("Relations", function() {
             "content": {
                 "topic": "orig",
             },
+            "state_key": "",
         });
         const badlyEditedTopic = new MatrixEvent({
             "sender": userId,
@@ -161,22 +162,17 @@ describe("Relations", function() {
                     "rel_type": "m.replace",
                 },
             },
+            "state_key": "",
         });
 
-        // Add the original topic and check results
-        {
-            relations.addEvent(originalTopic);
-            expect(originalTopic.replacingEvent()).toBe(null);
-            expect(originalTopic.getContent().topic).toBe("orig");
-        }
+        await relations.setTargetEvent(originalTopic);
+        expect(originalTopic.replacingEvent()).toBe(null);
+        expect(originalTopic.getContent().topic).toBe("orig");
 
-        // Add the badly edited topic and check results
-        {
-            relations.addEvent(badlyEditedTopic);
-            expect(originalTopic.replacingEvent()).toBe(null);
-            expect(originalTopic.getContent().topic).toBe("orig");
-            expect(badlyEditedTopic.replacingEvent()).toBe(null);
-            expect(badlyEditedTopic.getContent().topic).toBe("topic");
-        }
+        await relations.addEvent(badlyEditedTopic);
+        expect(originalTopic.replacingEvent()).toBe(null);
+        expect(originalTopic.getContent().topic).toBe("orig");
+        expect(badlyEditedTopic.replacingEvent()).toBe(null);
+        expect(badlyEditedTopic.getContent().topic).toBe("topic");
     });
 });