events: Don't require threads to contain m.in_reply_to

crates/ruma-common/src/events/relation.rs

@@ -188,7 +188,7 @@ pub struct Thread {
     /// If this event is not a reply, this is used as a fallback mechanism for clients that do not
     /// support threads. This should point to the latest message-like event in the thread and
     /// `is_falling_back` must be set to `true`.
-    pub in_reply_to: InReplyTo,
+    pub in_reply_to: Option<InReplyTo>,
 
     /// Whether the `m.in_reply_to` field is a fallback for older clients or a genuine reply in a
     /// thread.
@@ -199,13 +199,17 @@ impl Thread {
     /// Convenience method to create a regular `Thread` with the given event ID and latest
     /// message-like event ID.
     pub fn plain(event_id: OwnedEventId, latest_event_id: OwnedEventId) -> Self {
-        Self { event_id, in_reply_to: InReplyTo::new(latest_event_id), is_falling_back: true }
+        Self { event_id, in_reply_to: Some(InReplyTo::new(latest_event_id)), is_falling_back: true }
     }
 
     /// Convenience method to create a reply `Thread` with the given event ID and replied-to event
     /// ID.
     pub fn reply(event_id: OwnedEventId, reply_to_event_id: OwnedEventId) -> Self {
-        Self { event_id, in_reply_to: InReplyTo::new(reply_to_event_id), is_falling_back: false }
+        Self {
+            event_id,
+            in_reply_to: Some(InReplyTo::new(reply_to_event_id)),
+            is_falling_back: false,
+        }
     }
 }
 

crates/ruma-common/src/events/room/encrypted/relation_serde.rs

@@ -16,10 +16,7 @@ where
         | RelationJsonRepr::ThreadUnstable(ThreadUnstableJsonRepr { event_id, is_falling_back }),
     ) = ev.relates_to.relation
     {
-        let in_reply_to = ev
+        let in_reply_to = ev.relates_to.in_reply_to;
-            .relates_to
-            .in_reply_to
-            .ok_or_else(|| serde::de::Error::missing_field("m.in_reply_to"))?;
         return Ok(Some(Relation::Thread(Thread { event_id, in_reply_to, is_falling_back })));
     }
     let rel = if let Some(in_reply_to) = ev.relates_to.in_reply_to {
@@ -69,7 +66,7 @@ impl Serialize for Relation {
             }
             Relation::Thread(Thread { event_id, in_reply_to, is_falling_back }) => {
                 RelatesToJsonRepr {
-                    in_reply_to: Some(in_reply_to.clone()),
+                    in_reply_to: in_reply_to.clone(),
                     relation: Some(RelationJsonRepr::ThreadStable(ThreadStableJsonRepr {
                         event_id: event_id.clone(),
                         is_falling_back: *is_falling_back,

crates/ruma-common/src/events/room/message.rs

@@ -213,7 +213,7 @@ impl RoomMessageEventContent {
 
         self.relates_to = Some(Relation::Thread(Thread {
             event_id: thread_root,
-            in_reply_to: InReplyTo { event_id: previous_message.event_id.clone() },
+            in_reply_to: Some(InReplyTo { event_id: previous_message.event_id.clone() }),
             is_falling_back: is_reply == ReplyWithinThread::No,
         }));
 

crates/ruma-common/src/events/room/message/relation_serde.rs

@@ -32,10 +32,7 @@ where
         | RelationJsonRepr::ThreadUnstable(ThreadUnstableJsonRepr { event_id, is_falling_back }),
     ) = ev.relates_to.relation
     {
-        let in_reply_to = ev
+        let in_reply_to = ev.relates_to.in_reply_to;
-            .relates_to
-            .in_reply_to
-            .ok_or_else(|| serde::de::Error::missing_field("m.in_reply_to"))?;
         return Ok(Some(Relation::Thread(Thread { event_id, in_reply_to, is_falling_back })));
     }
 
@@ -92,7 +89,7 @@ where
             }
             Relation::Thread(Thread { event_id, in_reply_to, is_falling_back }) => {
                 EventWithRelatesToJsonRepr::new(RelatesToJsonRepr {
-                    in_reply_to: Some(in_reply_to.clone()),
+                    in_reply_to: in_reply_to.clone(),
                     relation: Some(RelationJsonRepr::ThreadStable(ThreadStableJsonRepr {
                         event_id: event_id.clone(),
                         is_falling_back: *is_falling_back,

crates/ruma-common/tests/events/encrypted.rs

@@ -381,7 +381,7 @@ fn content_thread_deserialization() {
         Some(Relation::Thread(thread)) => thread
     );
     assert_eq!(thread.event_id, "$thread_root");
-    assert_eq!(thread.in_reply_to.event_id, "$prev_event");
+    assert_eq!(thread.in_reply_to.unwrap().event_id, "$prev_event");
     assert!(!thread.is_falling_back);
 }
 

crates/ruma-common/tests/events/relations.rs

@@ -174,6 +174,30 @@ fn thread_reply_serialize() {
 
 #[test]
 fn thread_stable_deserialize() {
+    let json = json!({
+        "msgtype": "m.text",
+        "body": "<text msg>",
+        "m.relates_to": {
+            "rel_type": "m.thread",
+            "event_id": "$1598361704261elfgc",
+        },
+    });
+
+    let thread = assert_matches!(
+        from_json_value::<RoomMessageEventContent>(json),
+        Ok(RoomMessageEventContent {
+            msgtype: MessageType::Text(_),
+            relates_to: Some(Relation::Thread(thread)),
+            ..
+        }) => thread
+    );
+    assert_eq!(thread.event_id, "$1598361704261elfgc");
+    assert_matches!(thread.in_reply_to, None);
+    assert!(!thread.is_falling_back);
+}
+
+#[test]
+fn thread_stable_reply_deserialize() {
     let json = json!({
         "msgtype": "m.text",
         "body": "<text msg>",
@@ -195,7 +219,7 @@ fn thread_stable_deserialize() {
         }) => thread
     );
     assert_eq!(thread.event_id, "$1598361704261elfgc");
-    assert_eq!(thread.in_reply_to.event_id, "$latesteventid");
+    assert_eq!(thread.in_reply_to.unwrap().event_id, "$latesteventid");
     assert!(!thread.is_falling_back);
 }
 
@@ -222,6 +246,6 @@ fn thread_unstable_deserialize() {
         }) => thread
     );
     assert_eq!(thread.event_id, "$1598361704261elfgc");
-    assert_eq!(thread.in_reply_to.event_id, "$latesteventid");
+    assert_eq!(thread.in_reply_to.unwrap().event_id, "$latesteventid");
     assert!(!thread.is_falling_back);
 }