message_list_data: Track if the data is rendered using message list id.

This is an easy way to track if a MessageListData is rendered.
Storing MessageList object would make us liable to cleanup the
MessageList object when the data is no longer in use.

Note that this is more like "likely / past rendered message list id",
we will have to check currently rendered message list data to verify
if the data object is really rendered.

web/src/message_list.js

@@ -48,6 +48,8 @@ export class MessageList {
             });
         }
 
+        this.data.set_rendered_message_list_id(this.id);
+
         // TODO: This property should likely just be inlined into
         // having the MessageListView code that needs to access it
         // query .data.filter directly.

web/src/message_list_data.ts

@@ -46,6 +46,11 @@ export class MessageListData {
     // This is a callback that is called when messages are added to the message list.
     add_messages_callback?: (messages: Message[], recipient_order_changed: boolean) => void;
 
+    // ID of the MessageList for which this MessageListData is the data.
+    // Using ID instead of the MessageList object itself to avoid circular dependencies
+    // and to allow MessageList objects to be easily garbage collected.
+    rendered_message_list_id: number | undefined;
+
     // MessageListData is a core data structure for keeping track of a
     // contiguous block of messages matching a given narrow that can
     // be displayed in a Zulip message feed.
@@ -64,6 +69,10 @@ export class MessageListData {
         this._selected_id = -1;
     }
 
+    set_rendered_message_list_id(rendered_message_list_id: number | undefined): void {
+        this.rendered_message_list_id = rendered_message_list_id;
+    }
+
     set_add_messages_callback(
         callback: (messages: Message[], rows_order_changed: boolean) => void,
     ): void {

web/src/message_lists.ts

@@ -97,6 +97,7 @@ export function set_current(msg_list: MessageList | undefined): void {
 function delete_message_list(message_list: MessageList): void {
     message_list.view.$list.remove();
     rendered_message_lists.delete(message_list.id);
+    message_list.data.set_rendered_message_list_id(undefined);
 }
 
 export function update_current_message_list(msg_list: MessageList | undefined): void {