timeline: use the previous content's membership info when it's missin…

…g from the current membership event

Synapse returns a bare `{ "membership": "leave" }` as the content of a
room membership event (for leave membership changes and likely others).
In this case, it'd still be nice to have some kind of display
name/avatar URL to show in UIs; it's possible to reuse information from
the previous member event, if available.

bindings/matrix-sdk-ffi/src/timeline/content.rs

@@ -16,10 +16,7 @@ use std::{collections::HashMap, sync::Arc};
 
 use matrix_sdk::{crypto::types::events::UtdCause, room::power_levels::power_level_user_changes};
 use matrix_sdk_ui::timeline::{PollResult, TimelineDetails};
-use ruma::events::{
-    room::{message::RoomMessageEventContentWithoutRelation, MediaSource},
-    FullStateEventContent,
-};
+use ruma::events::room::{message::RoomMessageEventContentWithoutRelation, MediaSource};
 use tracing::warn;
 
 use super::ProfileDetails;
@@ -35,7 +32,9 @@ impl TimelineItemContent {
 
         match &self.0 {
             Content::Message(_) => TimelineItemContentKind::Message,
+
             Content::RedactedMessage => TimelineItemContentKind::RedactedMessage,
+
             Content::Sticker(sticker) => {
                 let content = sticker.content();
                 TimelineItemContentKind::Sticker {
@@ -44,23 +43,23 @@ impl TimelineItemContent {
                     source: Arc::new(MediaSource::from(content.source.clone())),
                 }
             }
+
             Content::Poll(poll_state) => TimelineItemContentKind::from(poll_state.results()),
+
             Content::CallInvite => TimelineItemContentKind::CallInvite,
+
             Content::CallNotify => TimelineItemContentKind::CallNotify,
+
             Content::UnableToDecrypt(msg) => {
                 TimelineItemContentKind::UnableToDecrypt { msg: EncryptedMessage::new(msg) }
             }
+
             Content::MembershipChange(membership) => TimelineItemContentKind::RoomMembership {
                 user_id: membership.user_id().to_string(),
-                user_display_name: if let FullStateEventContent::Original { content, .. } =
-                    membership.content()
-                {
-                    content.displayname.clone()
-                } else {
-                    None
-                },
+                user_display_name: membership.display_name(),
                 change: membership.change().map(Into::into),
             },
+
             Content::ProfileChange(profile) => {
                 let (display_name, prev_display_name) = profile
                     .displayname_change()
@@ -82,16 +81,19 @@ impl TimelineItemContent {
                     prev_avatar_url: prev_avatar_url.flatten(),
                 }
             }
+
             Content::OtherState(state) => TimelineItemContentKind::State {
                 state_key: state.state_key().to_owned(),
                 content: state.content().into(),
             },
+
             Content::FailedToParseMessageLike { event_type, error } => {
                 TimelineItemContentKind::FailedToParseMessageLike {
                     event_type: event_type.to_string(),
                     error: error.to_string(),
                 }
             }
+
             Content::FailedToParseState { event_type, state_key, error } => {
                 TimelineItemContentKind::FailedToParseState {
                     event_type: event_type.to_string(),

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

@@ -432,6 +432,38 @@ impl RoomMembershipChange {
         &self.content
     }
 
+    /// Retrieve the member's display name from the current event, or, if
+    /// missing, from the one it replaced.
+    pub fn display_name(&self) -> Option<String> {
+        if let FullStateEventContent::Original { content, prev_content } = &self.content {
+            content
+                .displayname
+                .as_ref()
+                .or_else(|| {
+                    prev_content.as_ref().and_then(|prev_content| prev_content.displayname.as_ref())
+                })
+                .cloned()
+        } else {
+            None
+        }
+    }
+
+    /// Retrieve the avatar URL from the current event, or, if missing, from the
+    /// one it replaced.
+    pub fn avatar_url(&self) -> Option<OwnedMxcUri> {
+        if let FullStateEventContent::Original { content, prev_content } = &self.content {
+            content
+                .avatar_url
+                .as_ref()
+                .or_else(|| {
+                    prev_content.as_ref().and_then(|prev_content| prev_content.avatar_url.as_ref())
+                })
+                .cloned()
+        } else {
+            None
+        }
+    }
+
     /// The membership change induced by this event.
     ///
     /// If this returns `None`, it doesn't mean that there was no change, but

crates/matrix-sdk-ui/src/timeline/tests/basic.rs

@@ -31,7 +31,7 @@ use ruma::{
         },
         FullStateEventContent,
     },
-    owned_event_id, MilliSecondsSinceUnixEpoch,
+    owned_event_id, owned_mxc_uri, MilliSecondsSinceUnixEpoch,
 };
 use stream_assert::assert_next_matches;
 
@@ -191,7 +191,7 @@ async fn test_room_member() {
         .handle_live_state_event_with_state_key(
             &ALICE,
             ALICE.to_owned(),
-            third_room_member_content,
+            third_room_member_content.clone(),
             Some(second_room_member_content),
         )
         .await;
@@ -201,6 +201,48 @@ async fn test_room_member() {
     assert_matches!(profile.displayname_change(), Some(_));
     assert_matches!(profile.avatar_url_change(), None);
 
+    let mut fourth_room_member_content = RoomMemberEventContent::new(MembershipState::Join);
+    fourth_room_member_content.displayname = Some("Alice In Wonderland".to_owned());
+    fourth_room_member_content.avatar_url = Some(owned_mxc_uri!("mxc://lolcathost.io/abc"));
+    timeline
+        .handle_live_state_event_with_state_key(
+            &ALICE,
+            ALICE.to_owned(),
+            fourth_room_member_content.clone(),
+            Some(third_room_member_content),
+        )
+        .await;
+
+    let item = assert_next_matches!(stream, VectorDiff::PushBack { value } => value);
+    assert_let!(TimelineItemContent::ProfileChange(profile) = item.content());
+    assert_matches!(profile.displayname_change(), None);
+    assert_matches!(profile.avatar_url_change(), Some(_));
+
+    {
+        // No avatar or display name in the new room member event content, but it's
+        // possible to get the previous one using the getters.
+        let room_member_content = RoomMemberEventContent::new(MembershipState::Leave);
+
+        timeline
+            .handle_live_state_event_with_state_key(
+                &ALICE,
+                ALICE.to_owned(),
+                room_member_content,
+                Some(fourth_room_member_content),
+            )
+            .await;
+
+        let item = assert_next_matches!(stream, VectorDiff::PushBack { value } => value);
+        assert_let!(TimelineItemContent::MembershipChange(membership) = item.content());
+        assert_matches!(membership.display_name().as_deref(), Some("Alice In Wonderland"));
+        assert_matches!(
+            membership.avatar_url().map(|url| url.to_string()).as_deref(),
+            Some("mxc://lolcathost.io/abc")
+        );
+        assert_matches!(membership.content(), FullStateEventContent::Original { .. });
+        assert_matches!(membership.change(), Some(MembershipChange::Left));
+    }
+
     timeline
         .handle_live_redacted_state_event_with_state_key(
             &ALICE,