feat: frontend Model extender (#3646)

* feat: reintroduce frontend extenders
* chore: used `Routes` extender in bundled extensions
* chore: used `PostTypes` extender in bundled extensions
* chore: `yarn format`
* feat: `Model` frontend extender
* chore: naming
* chore(review): attributes can be nullable or undefined
* chore(review): delay extender implementation
* chore(review): unnecessary check
* chore(review): stay consistent
* chore: merge conflicts
* chore: unused import
* chore: multiline extenders
* feat: add Store extender

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

extensions/mentions/js/src/forum/addMentionedByList.js

@@ -1,7 +1,5 @@
 import app from 'flarum/forum/app';
 import { extend } from 'flarum/common/extend';
-import Model from 'flarum/common/Model';
-import Post from 'flarum/common/models/Post';
 import CommentPost from 'flarum/forum/components/CommentPost';
 import Link from 'flarum/common/components/Link';
 import PostPreview from 'flarum/forum/components/PostPreview';
@@ -10,8 +8,6 @@ import username from 'flarum/common/helpers/username';
 import icon from 'flarum/common/helpers/icon';
 
 export default function addMentionedByList() {
-  Post.prototype.mentionedBy = Model.hasMany('mentionedBy');
-
   function hidePreview() {
     this.$('.Post-mentionedBy-preview')
       .removeClass('in')

extensions/mentions/js/src/forum/extend.ts

@@ -1,4 +1,15 @@
 import Extend from 'flarum/common/extenders';
+import Post from 'flarum/common/models/Post';
+import User from 'flarum/common/models/User';
 import MentionsUserPage from './components/MentionsUserPage';
 
-export default [new Extend.Routes().add('user.mentions', '/u/:username/mentions', MentionsUserPage)];
+export default [
+  new Extend.Routes() //
+    .add('user.mentions', '/u/:username/mentions', MentionsUserPage),
+
+  new Extend.Model(Post) //
+    .hasMany<Post>('mentionedBy'),
+
+  new Extend.Model(User) //
+    .attribute<boolean>('canMentionGroups'),
+];

extensions/mentions/js/src/forum/index.js

@@ -21,8 +21,6 @@ import Model from 'flarum/common/Model';
 export { default as extend } from './extend';
 
 app.initializers.add('flarum-mentions', function () {
-  User.prototype.canMentionGroups = Model.attribute('canMentionGroups');
-
   // For every mention of a post inside a post's content, set up a hover handler
   // that shows a preview of the mentioned post.
   addPostMentionPreviews();