Make fallback user mentions support also match against the bot's room-specific username

It seems like Element iOS benefits from this.

src/bot/implementation.rs

@@ -172,6 +172,24 @@ impl Bot {
         self.matrix_link().user_id()
     }
 
+    pub(crate) async fn user_display_name_in_room(&self, room: &Room) -> Option<String> {
+        let bot_display_name = self
+            .room_display_name_fetcher()
+            .own_display_name_in_room(room)
+            .await;
+
+        match bot_display_name {
+            Ok(value) => value,
+            Err(err) => {
+                tracing::warn!(
+                    ?err,
+                    "Failed to fetch bot display name. Proceeding without it"
+                );
+                None
+            }
+        }
+    }
+
     pub(crate) fn reacting(&self) -> super::reacting::Reacting {
         super::reacting::Reacting::new(self.clone())
     }

src/bot/messaging.rs

@@ -239,8 +239,11 @@ impl Messaging {
             }
         };
 
+        let bot_display_name = self.bot.user_display_name_in_room(&room).await;
+
         let interaction_context = determine_interaction_context_for_room_event(
             self.bot.user_id(),
+            &bot_display_name,
             &room,
             &event,
             &payload,
@@ -279,7 +282,8 @@ impl Messaging {
             self.bot.admin_pattern_regexes().clone(),
             trigger_event_info,
             interaction_context.thread_info.clone(),
-        );
+        )
+        .with_bot_display_name(bot_display_name);
 
         let controller_type = crate::controller::determine_controller(
             self.bot.command_prefix(),

src/controller/chat_completion/mod.rs

@@ -383,24 +383,10 @@ async fn handle_stage_text_generation(
         _ => vec![],
     };
 
-    let bot_display_name = bot
+    let bot_user_prefixes_to_strip = create_list_of_bot_user_prefixes_to_strip(
-        .room_display_name_fetcher()
+        bot.user_id(),
-        .own_display_name_in_room(message_context.room())
+        message_context.bot_display_name(),
-        .await;
+    );
-
-    let bot_display_name = match bot_display_name {
-        Ok(value) => value,
-        Err(err) => {
-            tracing::warn!(
-                ?err,
-                "Failed to fetch bot display name. Proceeding without it"
-            );
-            None
-        }
-    };
-
-    let bot_user_prefixes_to_strip =
-        create_list_of_bot_user_prefixes_to_strip(bot.user_id(), &bot_display_name);
 
     let allowed_users = match controller_type {
         // Regular chat completion only operates on messages from allowed users.

src/conversation/matrix/utils/mod.rs

@@ -277,13 +277,14 @@ pub fn convert_matrix_native_event_to_matrix_message(
 #[tracing::instrument(name = "determine_interaction_context_for_room_event", skip_all, fields(room_id = room.room_id().as_str(), event_id = current_event.event_id.as_str()))]
 pub async fn determine_interaction_context_for_room_event(
     bot_user_id: &OwnedUserId,
+    bot_display_name: &Option<String>,
     room: &Room,
     current_event: &OriginalSyncRoomMessageEvent,
     current_event_payload: &MessagePayload,
     event_fetcher: &Arc<RoomEventFetcher>,
 ) -> anyhow::Result<Option<InteractionContext>> {
     let current_event_is_mentioning_bot =
-        is_event_mentioning_bot(&current_event.content, bot_user_id);
+        is_event_mentioning_bot(&current_event.content, bot_user_id, bot_display_name);
 
     let Some(relation) = &current_event.content.relates_to else {
         // This is a top-level message. We consider it the start of the thread.
@@ -305,6 +306,7 @@ pub async fn determine_interaction_context_for_room_event(
         Relation::Thread(thread) => {
             determine_interaction_context_for_room_event_related_to_thread(
                 bot_user_id,
+                bot_display_name,
                 room,
                 current_event,
                 event_fetcher,
@@ -329,6 +331,7 @@ pub async fn determine_interaction_context_for_room_event(
 
 async fn determine_interaction_context_for_room_event_related_to_thread(
     bot_user_id: &OwnedUserId,
+    bot_display_name: &Option<String>,
     room: &Room,
     current_event: &OriginalSyncRoomMessageEvent,
     event_fetcher: &Arc<RoomEventFetcher>,
@@ -389,6 +392,7 @@ async fn determine_interaction_context_for_room_event_related_to_thread(
         thread_start_timeline_event,
         thread_info.clone(),
         bot_user_id,
+        bot_display_name,
     )?;
 
     let Some(detailed_message_payload) = thread_start_detailed_message_payload else {
@@ -431,6 +435,7 @@ async fn determine_interaction_context_for_room_event_related_to_reply(
 fn is_event_mentioning_bot(
     event_content: &RoomMessageEventContent,
     bot_user_id: &OwnedUserId,
+    bot_display_name: &Option<String>,
 ) -> bool {
     if let Some(mentions) = &event_content.mentions {
         mentions
@@ -445,12 +450,17 @@ fn is_event_mentioning_bot(
         // As of 2024-10-03, at least Element iOS does not support the new Mentions specification
         // and is still quite widespread.
         //
-        // It may be even better to match not only against the MXID, but also against the bot's
-        // room-specific display name.
-        //
         // We may consider dropping this string-matching behavior altogether in the future,
         // so improving this compatibility block is not a high priority.
-        event_content.body().contains(bot_user_id.as_str())
+        if event_content.body().contains(bot_user_id.as_str()) {
+            return true;
+        }
+
+        if let Some(bot_display_name) = bot_display_name {
+            return event_content.body().contains(bot_display_name);
+        }
+
+        false
     }
 }
 
@@ -459,6 +469,7 @@ fn timeline_event_to_detailed_message_payload(
     timeline_event: TimelineEvent,
     thread_info: ThreadInfo,
     bot_user_id: &OwnedUserId,
+    bot_display_name: &Option<String>,
 ) -> anyhow::Result<Option<DetailedMessagePayload>> {
     let timeline_event_deserialized = match timeline_event.event.deserialize() {
         Ok(value) => value,
@@ -510,8 +521,11 @@ fn timeline_event_to_detailed_message_payload(
                     return Ok(None);
                 };
 
-                let is_mentioning_bot =
+                let is_mentioning_bot = is_event_mentioning_bot(
-                    is_event_mentioning_bot(&room_message_original.content, bot_user_id);
+                    &room_message_original.content,
+                    bot_user_id,
+                    bot_display_name,
+                );
 
                 (is_mentioning_bot, room_message_payload)
             } else {

src/entity/message_context.rs

@@ -15,6 +15,8 @@ pub struct MessageContext {
     admin_whitelist_regexes: Vec<regex::Regex>,
     trigger_event_info: TriggerEventInfo,
     thread_info: ThreadInfo,
+
+    bot_display_name: Option<String>,
 }
 
 impl MessageContext {
@@ -31,9 +33,20 @@ impl MessageContext {
             admin_whitelist_regexes,
             trigger_event_info,
             thread_info,
+
+            bot_display_name: None,
         }
     }
 
+    pub fn with_bot_display_name(mut self, value: Option<String>) -> Self {
+        self.bot_display_name = value;
+        self
+    }
+
+    pub fn bot_display_name(&self) -> &Option<String> {
+        &self.bot_display_name
+    }
+
     pub fn room(&self) -> &Room {
         &self.room
     }