DEV: Refactor composer-/topic-presence-display (#29455)

Re-land #29262 as the d-shared-edits incompatibility has now been resolved. This reverts commit a59c07fc45.

app/assets/javascripts/discourse/app/models/composer.js

@@ -187,6 +187,11 @@ export default class Composer extends RestModel {
 
   @service dialog;
 
+  @tracked topic;
+  @tracked post;
+  @tracked reply;
+  @tracked whisper;
+
   unlistTopic = false;
   noBump = false;
   draftSaving = false;
@@ -200,7 +205,6 @@ export default class Composer extends RestModel {
   @not("creatingPrivateMessage") notCreatingPrivateMessage;
   @not("privateMessage") notPrivateMessage;
   @or("creatingTopic", "editingFirstPost") topicFirstPost;
-  @equal("action", REPLY) replyingToTopic;
   @equal("composeState", OPEN) viewOpen;
   @equal("composeState", DRAFT) viewDraft;
   @equal("composeState", FULLSCREEN) viewFullscreen;
@@ -263,6 +267,14 @@ export default class Composer extends RestModel {
     return categoryId ? Category.findById(categoryId) : null;
   }
 
+  get replyingToTopic() {
+    return this.get("action") === REPLY;
+  }
+
+  get editingPost() {
+    return isEdit(this.get("action"));
+  }
+
   @discourseComputed("category.minimumRequiredTags")
   minimumRequiredTags(minimumRequiredTags) {
     return minimumRequiredTags || 0;
@@ -286,11 +298,6 @@ export default class Composer extends RestModel {
     );
   }
 
-  @discourseComputed("action")
-  editingPost(action) {
-    return isEdit(action);
-  }
-
   @observes("composeState")
   composeStateChanged() {
     const oldOpen = this.composerOpened;

app/assets/javascripts/discourse/app/services/presence.js

@@ -1,4 +1,5 @@
 import EmberObject, { computed } from "@ember/object";
+import { dependentKeyCompat } from "@ember/object/compat";
 import Evented from "@ember/object/evented";
 import { cancel, debounce, next, once, throttle } from "@ember/runloop";
 import Service, { service } from "@ember/service";
@@ -108,12 +109,11 @@ class PresenceChannel extends EmberObject.extend(Evented) {
     this.trigger("change", this);
   }
 
-  @computed("_presenceState.users", "subscribed")
+  @dependentKeyCompat
   get users() {
-    if (!this.subscribed) {
-      return;
+    if (this.get("subscribed")) {
+      return this.get("_presenceState.users");
     }
-    return this._presenceState?.users;
   }
 
   @computed("_presenceState.count", "subscribed")

app/assets/javascripts/discourse/tests/helpers/presence-pretender.js

@@ -34,10 +34,7 @@ export default function (helper) {
 }
 
 export function getChannelInfo(name) {
-  return (
-    channels[name] ||
-    (channels[name] = { count: 0, users: [], last_message_id: 0 })
-  );
+  return (channels[name] ||= { count: 0, users: [], last_message_id: 0 });
 }
 
 export async function joinChannel(name, user) {