refactor(timeline): enhance the Timeline::send() and Timeline::send_reply() APIs when the timeline is threaded

crates/matrix-sdk-ui/CHANGELOG.md

@@ -6,6 +6,12 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased] - ReleaseDate
 
+### Features
+
+- `Timeline::send()` will now automatically fill the thread relationship, if the timeline has a
+  thread focus, and the sent event doesn't have a prefilled `relates_to` field (i.e. a relationship).
+  ([5427](https://github.com/matrix-org/matrix-rust-sdk/pull/5427))
+
 ### Refactor
 
 - [**breaking**] The MSRV has been bumped to Rust 1.88.

crates/matrix-sdk-ui/src/timeline/mod.rs

@@ -33,7 +33,11 @@ use matrix_sdk::{
     deserialized_responses::TimelineEvent,
     event_cache::{EventCacheDropHandles, RoomEventCache},
     executor::JoinHandle,
-    room::{Receipts, Room, edit::EditedContent, reply::Reply},
+    room::{
+        Receipts, Room,
+        edit::EditedContent,
+        reply::{EnforceThread, Reply},
+    },
     send_queue::{RoomSendQueueError, SendHandle},
 };
 use mime::Mime;
@@ -46,7 +50,7 @@ use ruma::{
         poll::unstable_start::{NewUnstablePollStartEventContent, UnstablePollStartEventContent},
         receipt::{Receipt, ReceiptThread},
         room::{
-            message::RoomMessageEventContentWithoutRelation,
+            message::{ReplyWithinThread, RoomMessageEventContentWithoutRelation},
             pinned_events::RoomPinnedEventsEventContent,
         },
     },
@@ -270,18 +274,65 @@ impl Timeline {
     /// If sending the message fails, the local echo item will change its
     /// `send_state` to [`EventSendState::SendingFailed`].
     ///
+    /// This will do the right thing in the presence of threads:
+    /// - if this timeline is not focused on a thread, then it will send the
+    ///   event as is.
+    /// - if this is a threaded timeline, and the event to send is a room
+    ///   message without a relationship, it will automatically mark it as a
+    ///   thread reply with the correct reply fallback, and send it.
+    ///
     /// # Arguments
     ///
     /// * `content` - The content of the message event.
-    ///
-    /// [`MessageLikeUnsigned`]: ruma::events::MessageLikeUnsigned
-    /// [`SyncMessageLikeEvent`]: ruma::events::SyncMessageLikeEvent
     #[instrument(skip(self, content), fields(room_id = ?self.room().room_id()))]
-    pub async fn send(
-        &self,
-        content: AnyMessageLikeEventContent,
-    ) -> Result<SendHandle, RoomSendQueueError> {
-        self.room().send_queue().send(content).await
+    pub async fn send(&self, content: AnyMessageLikeEventContent) -> Result<SendHandle, Error> {
+        // If this is a room event we're sending in a threaded timeline, we add the
+        // thread relation ourselves.
+        if let AnyMessageLikeEventContent::RoomMessage(ref room_msg_content) = content
+            && room_msg_content.relates_to.is_none()
+            && let Some(thread_root) = self.controller.thread_root()
+        {
+            // The latest event id is used for the reply-to fallback, for clients which
+            // don't handle threads. It should be correctly set to the latest
+            // event in the thread, which the timeline instance might or might
+            // not know about; in this case, we do a best effort of filling it, and resort
+            // to using the thread root if we don't know about any event.
+            //
+            // Note: we could trigger a back-pagination if the timeline is empty, and wait
+            // for the results, if the timeline is too often empty.
+            let latest_event_id = self
+                .controller
+                .items()
+                .await
+                .iter()
+                .rev()
+                .find_map(|item| {
+                    if let TimelineItemKind::Event(event) = item.kind() {
+                        event.event_id().map(ToOwned::to_owned)
+                    } else {
+                        None
+                    }
+                })
+                .unwrap_or(thread_root);
+
+            let content = self
+                .room()
+                .make_reply_event(
+                    // Note: this `.into()` gets rid of the relation, but we've checked previously
+                    // that the `relates_to` field wasn't set.
+                    room_msg_content.clone().into(),
+                    Reply {
+                        event_id: latest_event_id,
+                        enforce_thread: EnforceThread::Threaded(ReplyWithinThread::No),
+                    },
+                )
+                .await?;
+
+            Ok(self.room().send_queue().send(content.into()).await?)
+        } else {
+            // Otherwise, we send the message as is.
+            Ok(self.room().send_queue().send(content).await?)
+        }
     }
 
     /// Send a reply to the given event.

crates/matrix-sdk-ui/tests/integration/timeline/thread.rs

@@ -19,7 +19,6 @@ use eyeball_im::VectorDiff;
 use futures_util::StreamExt as _;
 use matrix_sdk::{
     assert_let_timeout,
-    room::reply::{EnforceThread, Reply},
     test_utils::mocks::{MatrixMockServer, RoomRelationsResponseTemplate},
 };
 use matrix_sdk_test::{
@@ -32,8 +31,9 @@ use ruma::{
     api::client::receipt::create_receipt::v3::ReceiptType as SendReceiptType,
     event_id,
     events::{
+        AnySyncTimelineEvent,
         receipt::{ReceiptThread, ReceiptType},
-        room::message::{ReplyWithinThread, RoomMessageEventContentWithoutRelation},
+        room::message::{Relation, ReplacementMetadata, RoomMessageEventContent},
     },
     owned_event_id, room_id, user_id,
 };
@@ -732,17 +732,12 @@ async fn test_thread_timeline_gets_local_echoes() {
     // update.
     let sent_event_id = event_id!("$sent_msg");
     server.mock_room_state_encryption().plain().mount().await;
-    server.mock_room_send().ok(sent_event_id).mock_once().mount().await;
-    timeline
-        .send_reply(
-            RoomMessageEventContentWithoutRelation::text_plain("hello to you too!"),
-            Reply {
-                event_id: threaded_event_id.to_owned(),
-                enforce_thread: EnforceThread::Threaded(ReplyWithinThread::No),
-            },
-        )
-        .await
-        .unwrap();
+
+    let (event_receiver, mock_builder) =
+        server.mock_room_send().ok_with_capture(sent_event_id, *ALICE);
+    mock_builder.mock_once().mount().await;
+
+    timeline.send(RoomMessageEventContent::text_plain("hello to you too!").into()).await.unwrap();
 
     // I get the local echo for the in-thread event.
     assert_let_timeout!(Some(timeline_updates) = stream.next());
@@ -753,19 +748,41 @@ async fn test_thread_timeline_gets_local_echoes() {
     assert!(event_item.is_local_echo());
     assert!(event_item.event_id().is_none());
 
+    // The thread information is properly filled.
+    let msglike = event_item.content().as_msglike().unwrap();
+    assert_eq!(msglike.thread_root.as_ref(), Some(&thread_root_event_id));
+    assert!(msglike.in_reply_to.is_none());
+
     // Then the local echo morphs into a sent local echo.
     assert_let_timeout!(Some(timeline_updates) = stream.next());
     assert_eq!(timeline_updates.len(), 1);
 
     assert_let!(VectorDiff::Set { index: 2, value } = &timeline_updates[0]);
     let event_item = value.as_event().unwrap();
     assert_eq!(event_item.event_id(), Some(sent_event_id));
-    assert_eq!(event_item.event_id(), Some(sent_event_id));
     assert!(event_item.content().reactions().unwrap().is_empty());
 
     // Then nothing else.
     assert_pending!(stream);
 
+    // The raw event includes the correctly reply-to fallback.
+    {
+        let raw_event = event_receiver.await.unwrap();
+        let event = raw_event.deserialize().unwrap();
+        assert_let!(
+            AnySyncTimelineEvent::MessageLike(
+                ruma::events::AnySyncMessageLikeEvent::RoomMessage(event)
+            ) = event
+        );
+        let event = event.as_original().unwrap();
+        assert_let!(Some(Relation::Thread(thread)) = event.content.relates_to.clone());
+        assert_eq!(thread.event_id, thread_root_event_id);
+        assert!(thread.is_falling_back);
+        // The reply-to fallback is set to the latest in-thread event, not the thread
+        // root.
+        assert_eq!(thread.in_reply_to.unwrap().event_id, threaded_event_id);
+    }
+
     // If I send a reaction for the in-thread event, the timeline gets updated, even
     // though the reaction doesn't mention the thread directly.
     server.mock_room_send().ok(event_id!("$reaction_id")).mock_once().mount().await;
@@ -791,6 +808,94 @@ async fn test_thread_timeline_gets_local_echoes() {
     assert_pending!(stream);
 }
 
+#[async_test]
+async fn test_thread_timeline_can_send_edit() {
+    // If I send an edit to a threaded timeline, it just works (aka the system to
+    // set the threaded relationship doesn't kick in, since there's already a
+    // relationship).
+
+    let server = MatrixMockServer::new().await;
+    let client = server.client_builder().build().await;
+
+    let room_id = room_id!("!a:b.c");
+    let thread_root_event_id = owned_event_id!("$root");
+    let threaded_event_id = event_id!("$threaded_event");
+
+    let room = server.sync_joined_room(&client, room_id).await;
+
+    let timeline = room
+        .timeline_builder()
+        .with_focus(TimelineFocus::Thread { root_event_id: thread_root_event_id.clone() })
+        .build()
+        .await
+        .unwrap();
+
+    let (initial_items, mut stream) = timeline.subscribe().await;
+
+    // At first, the timeline is empty.
+    assert!(initial_items.is_empty());
+    assert_pending!(stream);
+
+    // Start the timeline with an in-thread event.
+    let f = EventFactory::new();
+    server
+        .sync_room(
+            &client,
+            JoinedRoomBuilder::new(room_id).add_timeline_event(
+                f.text_msg("hello world")
+                    .sender(*ALICE)
+                    .event_id(threaded_event_id)
+                    .in_thread(&thread_root_event_id, threaded_event_id)
+                    .server_ts(MilliSecondsSinceUnixEpoch::now()),
+            ),
+        )
+        .await;
+
+    // Sanity check: I receive the event and the date divider.
+    assert_let_timeout!(Some(timeline_updates) = stream.next());
+    assert_eq!(timeline_updates.len(), 2);
+
+    // If I send an edit to an in-thread event, the timeline receives an update.
+    // Note: it's a bit far fetched to send an edit without using
+    // `Timeline::edit()`, but since it's possible…
+    let sent_event_id = event_id!("$sent_msg");
+    server.mock_room_state_encryption().plain().mount().await;
+
+    // No mock_once here: this endpoint may or may not be called, depending on
+    // timing of the end of the test.
+    server.mock_room_send().ok(sent_event_id).mount().await;
+
+    timeline
+        .send(
+            RoomMessageEventContent::text_plain("bonjour monde")
+                .make_replacement(
+                    ReplacementMetadata::new(threaded_event_id.to_owned(), None),
+                    None,
+                )
+                .into(),
+        )
+        .await
+        .unwrap();
+
+    // I get the local echo for the in-thread event.
+    assert_let_timeout!(Some(timeline_updates) = stream.next());
+    assert_eq!(timeline_updates.len(), 1);
+
+    assert_let!(VectorDiff::Set { index: 1, value } = &timeline_updates[0]);
+    let event_item = value.as_event().unwrap();
+
+    // The thread information is (still) present.
+    let msglike = event_item.content().as_msglike().unwrap();
+    assert_eq!(msglike.thread_root.as_ref(), Some(&thread_root_event_id));
+    assert!(msglike.in_reply_to.is_none());
+
+    // Text is eagerly updated.
+    assert_eq!(msglike.as_message().unwrap().body(), "bonjour monde");
+
+    // Then we're done.
+    assert_pending!(stream);
+}
+
 #[async_test]
 async fn test_sending_read_receipt_with_no_events_doesnt_unset_read_flag() {
     // If a thread timeline has no events, then marking it as read doesn't unset the