room: Count our own user's membership changes as activity

That way freshly joined or newly created rooms are at the top of the
list.

src/session/model/room/mod.rs

@@ -782,7 +782,7 @@ mod imp {
         }
 
         /// The member corresponding to our own user.
-        fn own_member(&self) -> &Member {
+        pub(super) fn own_member(&self) -> &Member {
             self.own_member.get().expect("Own member was initialized")
         }
 
@@ -2009,10 +2009,11 @@ impl Room {
     ///
     /// The events must be in reverse chronological order.
     fn update_latest_activity<'a>(&self, events: impl Iterator<Item = &'a Event>) {
+        let own_user_id = self.imp().own_member().user_id();
         let mut latest_activity = self.latest_activity();
 
         for event in events {
-            if event.counts_as_unread() {
+            if event.counts_as_activity(own_user_id) {
                 latest_activity = latest_activity.max(event.origin_server_ts().get().into());
                 break;
             }

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

@@ -9,7 +9,7 @@ use matrix_sdk_ui::timeline::{
 use ruma::{
     events::{receipt::Receipt, AnySyncTimelineEvent, TimelineEventType},
     serde::Raw,
-    MatrixToUri, MilliSecondsSinceUnixEpoch, OwnedEventId, OwnedTransactionId, OwnedUserId,
+    MatrixToUri, MilliSecondsSinceUnixEpoch, OwnedEventId, OwnedTransactionId, OwnedUserId, UserId,
 };
 use serde::{de::IgnoredAny, Deserialize};
 use tracing::{debug, error};
@@ -744,6 +744,15 @@ impl Event {
         self.item().content().counts_as_unread()
     }
 
+    /// Whether this `Event` can count as activity in a room.
+    ///
+    /// This includes content that counts as unread, plus membership changes for
+    /// our own user towards joining a room, so that freshly joined rooms are at
+    /// the top of the list.
+    pub(crate) fn counts_as_activity(&self, own_user_id: &UserId) -> bool {
+        self.item().content().counts_as_activity(own_user_id)
+    }
+
     /// The `matrix.to` URI representation for this event.
     ///
     /// Returns `None` if we don't have the ID of the event.

src/utils/matrix/ext_traits.rs

@@ -4,12 +4,13 @@ use std::borrow::Cow;
 
 use gtk::{glib, prelude::*};
 use matrix_sdk_ui::timeline::{
-    AnyOtherFullStateEventContent, EventTimelineItem, Message, TimelineEventItemId,
-    TimelineItemContent,
+    AnyOtherFullStateEventContent, EventTimelineItem, MembershipChange, Message,
+    TimelineEventItemId, TimelineItemContent,
 };
 use ruma::{
     events::{room::message::MessageType, AnySyncTimelineEvent},
     serde::Raw,
+    UserId,
 };
 use serde::Deserialize;
 
@@ -90,6 +91,13 @@ pub(crate) trait TimelineItemContentExt {
     /// [MSC2654]: https://github.com/matrix-org/matrix-spec-proposals/pull/2654
     fn counts_as_unread(&self) -> bool;
 
+    /// Whether this content can count as the latest activity in a room.
+    ///
+    /// This includes content that counts as unread, plus membership changes for
+    /// our own user towards joining a room, so that freshly joined rooms are at
+    /// the top of the list.
+    fn counts_as_activity(&self, own_user_id: &UserId) -> bool;
+
     /// Whether we can show the header for this content.
     fn can_show_header(&self) -> bool;
 
@@ -112,6 +120,40 @@ impl TimelineItemContentExt for TimelineItemContent {
         }
     }
 
+    fn counts_as_activity(&self, own_user_id: &UserId) -> bool {
+        if self.counts_as_unread() {
+            return true;
+        }
+
+        match self {
+            TimelineItemContent::MembershipChange(membership) => {
+                if membership.user_id() != own_user_id {
+                    return false;
+                }
+
+                // We need to bump the room for every meaningful change towards joining a room.
+                //
+                // The change cannot be computed in two cases:
+                // - This is the first membership event for our user in the room: we need to
+                //   count it.
+                // - The event was redacted: we do not know if we should count it or not, so we
+                //   count it too for simplicity.
+                membership.change().is_none_or(|change| {
+                    matches!(
+                        change,
+                        MembershipChange::Joined
+                            | MembershipChange::Unbanned
+                            | MembershipChange::Invited
+                            | MembershipChange::InvitationAccepted
+                            | MembershipChange::KnockAccepted
+                            | MembershipChange::Knocked
+                    )
+                })
+            }
+            _ => false,
+        }
+    }
+
     fn can_show_header(&self) -> bool {
         match self {
             TimelineItemContent::Message(message) => {