timeline: Attempt to minimize the diff batches from the SDK

A recent change in the SDK made them less optimized than before,
it creates jumps in the room history when sending a message.

We try to work around that by optimizing the batch ourselves.

Cargo.lock

@@ -1026,6 +1026,12 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "diff"
+version = "0.1.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -1349,6 +1355,7 @@ name = "fractal"
 version = "10.0.0-beta"
 dependencies = [
  "ashpd",
+ "diff",
  "djb_hash",
  "futures-channel",
  "futures-util",

Cargo.toml

@@ -21,6 +21,7 @@ codegen-units = 16
 
 # Please keep dependencies sorted.
 [dependencies]
+diff = "0.1"
 djb_hash = "0.1"
 futures-channel = "0.3"
 futures-util = "0.3"

src/prelude.rs

@@ -4,7 +4,7 @@ pub(crate) use crate::{
         ToastableDialogImpl,
     },
     contrib::CameraExt,
-    session::model::UserExt,
+    session::model::{TimelineItemExt, UserExt},
     session_list::SessionInfoExt,
     user_facing_error::UserFacingError,
     utils::{

src/session/model/room/event/mod.rs

@@ -182,10 +182,6 @@ mod imp {
     }
 
     impl TimelineItemImpl for Event {
-        fn id(&self) -> String {
-            format!("Event::{:?}", self.identifier())
-        }
-
         fn can_hide_header(&self) -> bool {
             self.item().content().can_show_header()
         }
@@ -509,9 +505,10 @@ glib::wrapper! {
 
 impl Event {
     /// Create a new `Event` in the given room with the given SDK timeline item.
-    pub fn new(item: EventTimelineItem, room: &Room) -> Self {
+    pub fn new(item: EventTimelineItem, room: &Room, timeline_id: &str) -> Self {
         let obj = glib::Object::builder::<Self>()
             .property("room", room)
+            .property("timeline-id", timeline_id)
             .build();
 
         obj.imp().set_item(item);
@@ -522,26 +519,14 @@ impl Event {
     /// Try to update this event with the given SDK timeline item.
     ///
     /// Returns `true` if the update succeeded.
-    pub(crate) fn try_update_with(&self, item: &EventTimelineItem) -> bool {
+    pub(crate) fn try_update_with(&self, item: &EventTimelineItem, timeline_id: &str) -> bool {
-        let imp = self.imp();
+        let is_same_item = self.timeline_id() == timeline_id;
 
-        match &self.identifier() {
+        if is_same_item {
-            TimelineEventItemId::TransactionId(txn_id)
+            self.imp().set_item(item.clone());
-                if item.transaction_id().is_some_and(|id| id == txn_id) =>
-            {
-                imp.set_item(item.clone());
-                return true;
-            }
-            TimelineEventItemId::EventId(event_id)
-                if item.event_id().is_some_and(|id| id == event_id) =>
-            {
-                imp.set_item(item.clone());
-                return true;
-            }
-            _ => {}
         }
 
-        false
+        is_same_item
     }
 
     /// The underlying SDK timeline item.

src/session/model/room/timeline/mod.rs

@@ -1,7 +1,11 @@
 mod timeline_item;
 mod virtual_item;
 
-use std::{collections::HashMap, ops::ControlFlow, sync::Arc};
+use std::{
+    collections::{HashMap, VecDeque},
+    ops::ControlFlow,
+    sync::Arc,
+};
 
 use futures_util::StreamExt;
 use gtk::{
@@ -11,7 +15,7 @@ use gtk::{
     subclass::prelude::*,
 };
 use matrix_sdk_ui::{
-    eyeball_im::VectorDiff,
+    eyeball_im::{Vector, VectorDiff},
     timeline::{
         default_event_filter, RoomExt, Timeline as SdkTimeline, TimelineEventItemId,
         TimelineItem as SdkTimelineItem,
@@ -28,7 +32,7 @@ use tokio::task::AbortHandle;
 use tracing::error;
 
 pub(crate) use self::{
-    timeline_item::{TimelineItem, TimelineItemImpl},
+    timeline_item::{TimelineItem, TimelineItemExt, TimelineItemImpl},
     virtual_item::{VirtualItem, VirtualItemKind},
 };
 use super::{Event, Room};
@@ -208,16 +212,16 @@ mod imp {
             let matrix_timeline = Arc::new(matrix_timeline);
             self.matrix_timeline
                 .set(matrix_timeline.clone())
-                .expect("matrix timeline was uninitialized");
+                .expect("matrix timeline is uninitialized");
 
-            let (values, timeline_stream) = matrix_timeline.subscribe().await;
+            let (values, timeline_stream) = matrix_timeline.subscribe_batched().await;
 
             if !values.is_empty() {
-                self.update(VectorDiff::Append { values });
+                self.update_with_single_diff(VectorDiff::Append { values }, &room);
             }
 
             let obj_weak = glib::SendWeakRef::from(self.obj().downgrade());
-            let fut = timeline_stream.for_each(move |diff| {
+            let fut = timeline_stream.for_each(move |diff_list| {
                 let obj_weak = obj_weak.clone();
                 let room_id = room_id.clone();
                 async move {
@@ -225,7 +229,7 @@ mod imp {
                     ctx.spawn(async move {
                         spawn!(async move {
                             if let Some(obj) = obj_weak.upgrade() {
-                                obj.imp().update(diff);
+                                obj.imp().update_with_diff_list(diff_list);
                             } else {
                                 error!(
                                     "Could not send timeline diff for room {room_id}: \
@@ -238,7 +242,9 @@ mod imp {
             });
 
             let diff_handle = spawn_tokio!(fut);
-            self.diff_handle.set(diff_handle.abort_handle()).unwrap();
+            self.diff_handle
+                .set(diff_handle.abort_handle())
+                .expect("handle is uninitialized");
 
             self.watch_read_receipts().await;
             self.set_state(TimelineState::Ready);
@@ -266,15 +272,148 @@ mod imp {
             self.obj().notify_has_room_create();
         }
 
-        /// Update this `Timeline` with the given diff.
+        /// Update this timeline with the given diff list.
-        #[allow(clippy::too_many_lines)]
+        fn update_with_diff_list(&self, diff_list: Vec<VectorDiff<Arc<SdkTimelineItem>>>) {
-        fn update(&self, diff: VectorDiff<Arc<SdkTimelineItem>>) {
             let Some(room) = self.room.upgrade() else {
                 return;
             };
-            let sdk_items = &self.sdk_items;
             let was_empty = self.is_empty();
 
+            let diff_list = self.minimize_diff_list(diff_list);
+
+            for diff in diff_list {
+                self.update_with_single_diff(diff, &room);
+            }
+
+            let obj = self.obj();
+            if self.is_empty() != was_empty {
+                obj.notify_is_empty();
+            }
+
+            obj.emit_read_change_trigger();
+        }
+
+        /// Attempt to minimize the given list of diffs.
+        ///
+        /// This is necessary because the SDK diffs are not always optimized,
+        /// e.g. an item is removed then re-added, which creates jumps in the
+        /// room history.
+        fn minimize_diff_list(
+            &self,
+            diff_list: Vec<VectorDiff<Arc<SdkTimelineItem>>>,
+        ) -> Vec<VectorDiff<Arc<SdkTimelineItem>>> {
+            let mut old_items = Vec::with_capacity(self.sdk_items.n_items() as usize);
+
+            // Construct the current state.
+            for item in self.sdk_items.iter::<TimelineItem>() {
+                let Ok(item) = item else {
+                    // The list changed, return early.
+                    return diff_list;
+                };
+
+                old_items.push(item.timeline_id());
+            }
+
+            // Get the new state by applying the diffs.
+            let mut value_map = HashMap::with_capacity(diff_list.len());
+            let mut new_items = old_items.iter().cloned().collect::<VecDeque<_>>();
+
+            for diff in &diff_list {
+                match diff {
+                    VectorDiff::Append { values } => {
+                        new_items.reserve(values.len());
+
+                        for value in values {
+                            let timeline_id = value.unique_id().0.clone();
+                            value_map.insert(timeline_id.clone(), value.clone());
+                            new_items.push_back(timeline_id);
+                        }
+                    }
+                    VectorDiff::PushFront { value } => {
+                        let timeline_id = value.unique_id().0.clone();
+                        value_map.insert(timeline_id.clone(), value.clone());
+                        new_items.push_front(timeline_id);
+                    }
+                    VectorDiff::PushBack { value } => {
+                        let timeline_id = value.unique_id().0.clone();
+                        value_map.insert(timeline_id.clone(), value.clone());
+                        new_items.push_back(timeline_id);
+                    }
+                    VectorDiff::PopFront => {
+                        new_items.pop_front();
+                    }
+                    VectorDiff::PopBack => {
+                        new_items.pop_back();
+                    }
+                    VectorDiff::Insert { index, value } => {
+                        let timeline_id = value.unique_id().0.clone();
+                        value_map.insert(timeline_id.clone(), value.clone());
+                        new_items.insert(*index, timeline_id);
+                    }
+                    VectorDiff::Set { index, value } => {
+                        let timeline_id = value.unique_id().0.clone();
+                        value_map.insert(timeline_id.clone(), value.clone());
+
+                        let item = new_items.get_mut(*index).expect("item exists");
+                        *item = timeline_id;
+                    }
+                    VectorDiff::Remove { index } => {
+                        new_items.remove(*index);
+                    }
+                    VectorDiff::Clear | VectorDiff::Truncate { .. } | VectorDiff::Reset { .. } => {
+                        // Minimizing this will probably make a worse diff, so we return early.
+                        return diff_list;
+                    }
+                }
+            }
+
+            let new_items = Vec::from(new_items);
+            let mut min_diff_list = Vec::with_capacity(diff_list.len());
+            let mut index = 0;
+            let mut n_items = old_items.len();
+
+            for result in diff::slice(&old_items, &new_items) {
+                match result {
+                    diff::Result::Left(_) => {
+                        min_diff_list.push(VectorDiff::Remove { index });
+                        n_items -= 1;
+                    }
+                    diff::Result::Both(timeline_id, _) => {
+                        if let Some(value) = value_map.get(timeline_id).cloned() {
+                            min_diff_list.push(VectorDiff::Set { index, value });
+                        }
+                        index += 1;
+                    }
+                    diff::Result::Right(timeline_id) => {
+                        let value = value_map
+                            .get(timeline_id)
+                            .expect("value exists for added item")
+                            .clone();
+
+                        if index == n_items {
+                            if let Some(VectorDiff::Append { values }) = min_diff_list.last_mut() {
+                                values.push_back(value);
+                            } else {
+                                min_diff_list.push(VectorDiff::Append {
+                                    values: Vector::from([value]),
+                                });
+                            }
+                        } else {
+                            min_diff_list.push(VectorDiff::Insert { index, value });
+                        }
+
+                        index += 1;
+                        n_items += 1;
+                    }
+                }
+            }
+
+            min_diff_list
+        }
+
+        /// Update this timeline with the given diff.
+        #[allow(clippy::too_many_lines)]
+        fn update_with_single_diff(&self, diff: VectorDiff<Arc<SdkTimelineItem>>, room: &Room) {
             match diff {
                 VectorDiff::Append { values } => {
                     let new_list = values
@@ -282,10 +421,10 @@ mod imp {
                         .map(|item| self.create_item(&item))
                         .collect::<Vec<_>>();
 
-                    let pos = sdk_items.n_items();
+                    let pos = self.sdk_items.n_items();
                     let added = new_list.len() as u32;
 
-                    sdk_items.extend_from_slice(&new_list);
+                    self.sdk_items.extend_from_slice(&new_list);
                     self.update_items_headers(pos, added.max(1));
 
                     // Try to update the latest unread message.
@@ -294,14 +433,14 @@ mod imp {
                     );
                 }
                 VectorDiff::Clear => {
-                    sdk_items.remove_all();
+                    self.sdk_items.remove_all();
                     self.event_map.borrow_mut().clear();
                     self.set_has_room_create(false);
                 }
                 VectorDiff::PushFront { value } => {
                     let item = self.create_item(&value);
 
-                    sdk_items.insert(0, &item);
+                    self.sdk_items.insert(0, &item);
                     self.update_items_headers(0, 1);
 
                     // Try to update the latest unread message.
@@ -311,8 +450,8 @@ mod imp {
                 }
                 VectorDiff::PushBack { value } => {
                     let item = self.create_item(&value);
-                    let pos = sdk_items.n_items();
+                    let pos = self.sdk_items.n_items();
-                    sdk_items.append(&item);
+                    self.sdk_items.append(&item);
                     self.update_items_headers(pos, 1);
 
                     // Try to update the latest unread message.
@@ -321,24 +460,32 @@ mod imp {
                     }
                 }
                 VectorDiff::PopFront => {
-                    let item = sdk_items.item(0).and_downcast().unwrap();
+                    let item = self
+                        .sdk_items
+                        .item(0)
+                        .and_downcast()
+                        .expect("all items are TimelineItems");
                     self.remove_item(&item);
 
-                    sdk_items.remove(0);
+                    self.sdk_items.remove(0);
                     self.update_items_headers(0, 1);
                 }
                 VectorDiff::PopBack => {
-                    let pos = sdk_items.n_items() - 1;
+                    let pos = self.sdk_items.n_items() - 1;
-                    let item = sdk_items.item(pos).and_downcast().unwrap();
+                    let item = self
+                        .sdk_items
+                        .item(pos)
+                        .and_downcast()
+                        .expect("all items are TimelineItems");
                     self.remove_item(&item);
 
-                    sdk_items.remove(pos);
+                    self.sdk_items.remove(pos);
                 }
                 VectorDiff::Insert { index, value } => {
                     let pos = index as u32;
                     let item = self.create_item(&value);
 
-                    sdk_items.insert(pos, &item);
+                    self.sdk_items.insert(pos, &item);
                     self.update_items_headers(pos, 1);
 
                     // Try to update the latest unread message.
@@ -348,7 +495,11 @@ mod imp {
                 }
                 VectorDiff::Set { index, value } => {
                     let pos = index as u32;
-                    let prev_item = sdk_items.item(pos).and_downcast::<TimelineItem>().unwrap();
+                    let prev_item = self
+                        .sdk_items
+                        .item(pos)
+                        .and_downcast::<TimelineItem>()
+                        .expect("all items are TimelineItems");
 
                     let item = if prev_item.try_update_with(&value) {
                         if let Some(event) = prev_item.downcast_ref::<Event>() {
@@ -364,7 +515,7 @@ mod imp {
                         self.remove_item(&prev_item);
                         let item = self.create_item(&value);
 
-                        sdk_items.splice(pos, 1, &[item.clone()]);
+                        self.sdk_items.splice(pos, 1, &[item.clone()]);
 
                         item
                     };
@@ -379,22 +530,31 @@ mod imp {
                 }
                 VectorDiff::Remove { index } => {
                     let pos = index as u32;
-                    let item = sdk_items.item(pos).and_downcast().unwrap();
+                    let item = self
+                        .sdk_items
+                        .item(pos)
+                        .and_downcast()
+                        .expect("all items are TimelineItems");
                     self.remove_item(&item);
 
-                    sdk_items.remove(pos);
+                    self.sdk_items.remove(pos);
                     self.update_items_headers(pos, 1);
                 }
                 VectorDiff::Truncate { length } => {
                     let new_len = length as u32;
-                    let old_len = sdk_items.n_items();
+                    let old_len = self.sdk_items.n_items();
 
                     for pos in new_len..old_len {
-                        let item = sdk_items.item(pos).and_downcast().unwrap();
+                        let item = self
+                            .sdk_items
+                            .item(pos)
+                            .and_downcast()
+                            .expect("all items are TimelineItems");
                         self.remove_item(&item);
                     }
 
-                    sdk_items.splice(new_len, old_len - new_len, &[] as &[glib::Object]);
+                    self.sdk_items
+                        .splice(new_len, old_len - new_len, &[] as &[glib::Object]);
                 }
                 VectorDiff::Reset { values } => {
                     // Reset the state.
@@ -406,10 +566,10 @@ mod imp {
                         .map(|item| self.create_item(&item))
                         .collect::<Vec<_>>();
 
-                    let removed = sdk_items.n_items();
+                    let removed = self.sdk_items.n_items();
                     let added = new_list.len() as u32;
 
-                    sdk_items.splice(0, removed, &new_list);
+                    self.sdk_items.splice(0, removed, &new_list);
                     self.update_items_headers(0, added.max(1));
 
                     // Try to update the latest unread message.
@@ -418,13 +578,6 @@ mod imp {
                     );
                 }
             }
-
-            let obj = self.obj();
-            if self.is_empty() != was_empty {
-                obj.notify_is_empty();
-            }
-
-            obj.emit_read_change_trigger();
         }
 
         /// Update `nb` items' headers starting at `pos`.
@@ -625,7 +778,7 @@ mod imp {
             let handle = spawn_tokio!(fut);
             self.read_receipts_changed_handle
                 .set(handle.abort_handle())
-                .unwrap();
+                .expect("handle is uninitialized");
         }
     }
 }
@@ -738,7 +891,7 @@ impl Timeline {
                 .await
         })
         .await
-        .unwrap();
+        .expect("task was not aborted");
 
         let sdk_items = &self.imp().sdk_items;
         let count = sdk_items.n_items();

src/session/model/room/timeline/timeline_item.rs

@@ -6,14 +6,16 @@ use super::VirtualItem;
 use crate::session::model::{Event, Room};
 
 mod imp {
-    use std::{cell::Cell, marker::PhantomData};
+    use std::{
+        cell::{Cell, RefCell},
+        marker::PhantomData,
+    };
 
     use super::*;
 
     #[repr(C)]
     pub struct TimelineItemClass {
         parent_class: glib::object::ObjectClass,
-        pub(super) id: fn(&super::TimelineItem) -> String,
         pub(super) selectable: fn(&super::TimelineItem) -> bool,
         pub(super) can_hide_header: fn(&super::TimelineItem) -> bool,
         pub(super) event_sender_id: fn(&super::TimelineItem) -> Option<OwnedUserId>,
@@ -23,11 +25,6 @@ mod imp {
         type Type = TimelineItem;
     }
 
-    pub(super) fn timeline_item_id(this: &super::TimelineItem) -> String {
-        let klass = this.class();
-        (klass.as_ref().id)(this)
-    }
-
     pub(super) fn timeline_item_selectable(this: &super::TimelineItem) -> bool {
         let klass = this.class();
         (klass.as_ref().selectable)(this)
@@ -46,11 +43,9 @@ mod imp {
     #[derive(Debug, Default, glib::Properties)]
     #[properties(wrapper_type = super::TimelineItem)]
     pub struct TimelineItem {
-        /// A unique ID for this `TimelineItem`.
+        /// A unique ID for this `TimelineItem` in the local timeline.
-        ///
+        #[property(get, construct_only)]
-        /// For debugging purposes.
+        timeline_id: RefCell<String>,
-        #[property(get = Self::id)]
-        id: PhantomData<String>,
         /// Whether this `TimelineItem` is selectable.
         ///
         /// Defaults to `false`.
@@ -85,13 +80,6 @@ mod imp {
     impl ObjectImpl for TimelineItem {}
 
     impl TimelineItem {
-        /// A unique ID for this `TimelineItem`.
-        ///
-        /// For debugging purposes.
-        fn id(&self) -> String {
-            imp::timeline_item_id(&self.obj())
-        }
-
         /// Whether this `TimelineItem` is selectable.
         ///
         /// Defaults to `false`.
@@ -135,9 +123,11 @@ impl TimelineItem {
     ///
     /// Constructs the proper child type.
     pub fn new(item: &SdkTimelineItem, room: &Room) -> Self {
+        let timeline_id = &item.unique_id().0;
+
         match item.kind() {
-            TimelineItemKind::Event(event) => Event::new(event.clone(), room).upcast(),
+            TimelineItemKind::Event(event) => Event::new(event.clone(), room, timeline_id).upcast(),
-            TimelineItemKind::Virtual(item) => VirtualItem::new(item).upcast(),
+            TimelineItemKind::Virtual(item) => VirtualItem::with_item(item, timeline_id).upcast(),
         }
     }
 
@@ -145,14 +135,16 @@ impl TimelineItem {
     ///
     /// Returns `true` if the update succeeded.
     pub(crate) fn try_update_with(&self, item: &SdkTimelineItem) -> bool {
+        let timeline_id = &item.unique_id().0;
+
         match item.kind() {
             TimelineItemKind::Event(new_event) => {
                 if let Some(event) = self.downcast_ref::<Event>() {
-                    return event.try_update_with(new_event);
+                    return event.try_update_with(new_event, timeline_id);
                 }
             }
             TimelineItemKind::Virtual(_item) => {
-                // Always invalidate. It shouldn't happen often and updating
+                // Always invalidate. It should not happen often and updating
                 // those should be unexpensive.
             }
         }
@@ -168,10 +160,8 @@ impl TimelineItem {
 /// of `TimelineItemImpl`.
 #[allow(dead_code)]
 pub(crate) trait TimelineItemExt: 'static {
-    /// A unique ID for this `TimelineItem`.
+    /// A unique ID for this `TimelineItem` in the local timeline.
-    ///
+    fn timeline_id(&self) -> String;
-    /// For debugging purposes.
-    fn id(&self) -> String;
 
     /// Whether this `TimelineItem` is selectable.
     ///
@@ -198,8 +188,8 @@ pub(crate) trait TimelineItemExt: 'static {
 }
 
 impl<O: IsA<TimelineItem>> TimelineItemExt for O {
-    fn id(&self) -> String {
+    fn timeline_id(&self) -> String {
-        self.upcast_ref().id()
+        self.upcast_ref().timeline_id()
     }
 
     fn selectable(&self) -> bool {
@@ -229,8 +219,6 @@ impl<O: IsA<TimelineItem>> TimelineItemExt for O {
 /// Overriding a method from this Trait overrides also its behavior in
 /// `TimelineItemExt`.
 pub(crate) trait TimelineItemImpl: ObjectImpl {
-    fn id(&self) -> String;
-
     fn selectable(&self) -> bool {
         false
     }
@@ -255,7 +243,6 @@ where
 
         let klass = class.as_mut();
 
-        klass.id = id_trampoline::<T>;
         klass.selectable = selectable_trampoline::<T>;
         klass.can_hide_header = can_hide_header_trampoline::<T>;
         klass.event_sender_id = event_sender_id_trampoline::<T>;
@@ -263,15 +250,6 @@ where
 }
 
 // Virtual method implementation trampolines.
-fn id_trampoline<T>(this: &TimelineItem) -> String
-where
-    T: ObjectSubclass + TimelineItemImpl,
-    T::Type: IsA<TimelineItem>,
-{
-    let this = this.downcast_ref::<T::Type>().unwrap();
-    this.imp().id()
-}
-
 fn selectable_trampoline<T>(this: &TimelineItem) -> bool
 where
     T: ObjectSubclass + TimelineItemImpl,

src/session/model/room/timeline/virtual_item.rs

@@ -67,19 +67,7 @@ mod imp {
     #[glib::derived_properties]
     impl ObjectImpl for VirtualItem {}
 
-    impl TimelineItemImpl for VirtualItem {
+    impl TimelineItemImpl for VirtualItem {}
-        fn id(&self) -> String {
-            match &**self.kind.borrow() {
-                VirtualItemKind::Spinner => "VirtualItem::Spinner".to_owned(),
-                VirtualItemKind::Typing => "VirtualItem::Typing".to_owned(),
-                VirtualItemKind::TimelineStart => "VirtualItem::TimelineStart".to_owned(),
-                VirtualItemKind::DayDivider(date) => {
-                    format!("VirtualItem::DayDivider({})", date.format("%F").unwrap())
-                }
-                VirtualItemKind::NewMessages => "VirtualItem::NewMessages".to_owned(),
-            }
-        }
-    }
 }
 
 glib::wrapper! {
@@ -91,10 +79,12 @@ glib::wrapper! {
 
 impl VirtualItem {
     /// Create a new `VirtualItem` from a virtual timeline item.
-    pub fn new(item: &VirtualTimelineItem) -> Self {
+    pub fn with_item(item: &VirtualTimelineItem, timeline_id: &str) -> Self {
         match item {
-            VirtualTimelineItem::DateDivider(ts) => Self::day_divider_with_timestamp(*ts),
+            VirtualTimelineItem::DateDivider(ts) => {
-            VirtualTimelineItem::ReadMarker => Self::new_messages(),
+                Self::day_divider_with_timestamp(*ts, timeline_id)
+            }
+            VirtualTimelineItem::ReadMarker => Self::new_messages(timeline_id),
         }
     }
 
@@ -102,6 +92,7 @@ impl VirtualItem {
     pub(crate) fn spinner() -> Self {
         glib::Object::builder()
             .property("kind", VirtualItemKind::Spinner.boxed())
+            .property("timeline-id", "VirtualItemKind::Spinner")
             .build()
     }
 
@@ -109,6 +100,7 @@ impl VirtualItem {
     pub(crate) fn typing() -> Self {
         glib::Object::builder()
             .property("kind", VirtualItemKind::Typing.boxed())
+            .property("timeline-id", "VirtualItemKind::Typing")
             .build()
     }
 
@@ -116,13 +108,15 @@ impl VirtualItem {
     pub(crate) fn timeline_start() -> Self {
         glib::Object::builder()
             .property("kind", VirtualItemKind::TimelineStart.boxed())
+            .property("timeline-id", "VirtualItemKind::TimelineStart")
             .build()
     }
 
     /// Create a new messages virtual item.
-    pub(crate) fn new_messages() -> Self {
+    fn new_messages(timeline_id: &str) -> Self {
         glib::Object::builder()
             .property("kind", VirtualItemKind::NewMessages.boxed())
+            .property("timeline-id", timeline_id)
             .build()
     }
 
@@ -133,13 +127,17 @@ impl VirtualItem {
     /// current local time.
     ///
     /// Panics if an error occurred when accessing the current local time.
-    pub(crate) fn day_divider_with_timestamp(timestamp: MilliSecondsSinceUnixEpoch) -> Self {
+    fn day_divider_with_timestamp(
+        timestamp: MilliSecondsSinceUnixEpoch,
+        timeline_id: &str,
+    ) -> Self {
         let date = glib::DateTime::from_unix_utc(timestamp.as_secs().into())
             .or_else(|_| glib::DateTime::now_utc())
             .expect("We should be able to get the current time");
 
         glib::Object::builder()
             .property("kind", VirtualItemKind::DayDivider(date).boxed())
+            .property("timeline-id", timeline_id)
             .build()
     }
 }