[2.x] fix(flags): drop literal 'undefined' from Inappropriate reason and lazy-load FlagPostModal

Two related changes to the Inappropriate flag-post path:

1. When no Community Guidelines URL is configured, the reason text
   rendered the literal token "{undefined}" — the translator
   stringifies undefined values passed into a rich placeholder. Use
   a separate translation key with no link placeholder when the URL
   is unset, instead of trying to pass `undefined` as the `<a>` slot.

2. The flag modal was imported eagerly via a side-effect import in
   forum.ts and a static import in addFlagControl.js, so its ~4 KB
   was always shipped in the main forum bundle even for users who
   never report a post. Switch to the documented lazy-load pattern
   (`app.modal.show(() => import('./components/FlagPostModal'), ...)`)
   and declare the chunk directory via `Extend\Frontend::jsDirectory`
   so the chunked sub-bundle is published.

Closes #4574

Author: imorland

extensions/flags/extend.php

@@ -29,6 +29,7 @@
 return [
     (new Extend\Frontend('forum'))
         ->js(__DIR__.'/js/dist/forum.js')
+        ->jsDirectory(__DIR__.'/js/dist/forum')
         ->css(__DIR__.'/less/forum.less')
         ->route('/flags', 'flags', AssertRegistered::class),
 

extensions/flags/js/src/forum/addFlagControl.js

@@ -3,15 +3,13 @@ import app from 'flarum/forum/app';
 import PostControls from 'flarum/forum/utils/PostControls';
 import Button from 'flarum/common/components/Button';
 
-import FlagPostModal from './components/FlagPostModal';
-
 export default function () {
   extend(PostControls, 'userControls', function (items, post) {
     if (post.isHidden() || post.contentType() !== 'comment' || !post.canFlag()) return;
 
     items.add(
       'flag',
-      <Button icon="fas fa-flag" onclick={() => app.modal.show(FlagPostModal, { post })}>
+      <Button icon="fas fa-flag" onclick={() => app.modal.show(() => import('./components/FlagPostModal'), { post })}>
         {app.translator.trans('flarum-flags.forum.post_controls.flag_button')}
       </Button>
     );

extensions/flags/js/src/forum/components/FlagPostModal.js

@@ -92,9 +92,11 @@ export default class FlagPostModal extends FormModal {
           onclick={withAttr('value', this.reason)}
         />
         <strong>{app.translator.trans('flarum-flags.forum.flag_post.reason_inappropriate_label')}</strong>
-        {app.translator.trans('flarum-flags.forum.flag_post.reason_inappropriate_text', {
-          a: guidelinesUrl ? <a href={guidelinesUrl} target="_blank" /> : undefined,
-        })}
+        {guidelinesUrl
+          ? app.translator.trans('flarum-flags.forum.flag_post.reason_inappropriate_text', {
+              a: <a href={guidelinesUrl} target="_blank" />,
+            })
+          : app.translator.trans('flarum-flags.forum.flag_post.reason_inappropriate_text_no_guidelines')}
         {this.reason() === 'inappropriate' && (
           <textarea
             className="FormControl"

extensions/flags/js/src/forum/forum.ts

@@ -5,6 +5,5 @@ import './addFlagsDropdown';
 import './models/Flag';
 
 import './components/FlagList';
-import './components/FlagPostModal';
 import './components/FlagsPage';
 import './components/FlagsDropdown';

extensions/flags/locale/en.yml

@@ -28,6 +28,7 @@ flarum-flags:
       reason_details_placeholder: Additional details (optional)
       reason_inappropriate_label: Inappropriate
       reason_inappropriate_text: "This post is offensive, abusive, or violates our <a>community guidelines</a>."
+      reason_inappropriate_text_no_guidelines: This post is offensive or abusive.
       reason_missing_message: Please provide some details for our moderators.
       reason_off_topic_label: "Off-topic"
       reason_off_topic_text: This post is not relevant to the current discussion and should be moved elsewhere.