Handle post rendering errors to avoid bricking

js/src/common/models/Post.js

@@ -10,9 +10,11 @@ Object.assign(Post.prototype, {
 
   createdAt: Model.attribute('createdAt', Model.transformDate),
   user: Model.hasOne('user'),
+
   contentType: Model.attribute('contentType'),
   content: Model.attribute('content'),
   contentHtml: Model.attribute('contentHtml'),
+  renderFailed: Model.attribute('renderFailed'),
   contentPlain: computed('contentHtml', getPlainContent),
 
   editedAt: Model.attribute('editedAt', Model.transformDate),

js/src/forum/components/CommentPost.js

@@ -100,6 +100,7 @@ export default class CommentPost extends Post {
       ' ' +
       classList({
         CommentPost: true,
+        'Post--renderFailed': post.renderFailed(),
         'Post--hidden': post.isHidden(),
         'Post--edited': post.isEdited(),
         revealContent: this.revealContent,

less/forum/Post.less

@@ -185,6 +185,10 @@
   }
 }
 
+.Post--renderFailed {
+  background-color: @control-danger-color;
+}
+
 .Post--hidden {
   .Post-header, .Post-header a, .PostUser h3, .PostUser h3 a {
     color: @muted-more-color;

locale/core.yml

@@ -523,6 +523,7 @@ core:
       not_found_message: The requested resource was not found.
       permission_denied_message: You do not have permission to do that.
       rate_limit_exceeded_message: You're going a little too quickly. Please try again in a few seconds.
+      render_failed_message: The formatter was unable to format this content due to an error. Please check the Flarum error logs for more information.
 
     # These translations are used in the loading indicator component.
     loading_indicator:

src/Api/Serializer/BasicPostSerializer.php

@@ -9,9 +9,12 @@
 
 namespace Flarum\Api\Serializer;
 
+use Exception;
+use Flarum\Foundation\ErrorHandling\LogReporter;
 use Flarum\Post\CommentPost;
 use Flarum\Post\Post;
 use InvalidArgumentException;
+use Symfony\Contracts\Translation\TranslatorInterface;
 
 class BasicPostSerializer extends AbstractSerializer
 {
@@ -41,7 +44,14 @@ protected function getDefaultAttributes($post)
         ];
 
         if ($post instanceof CommentPost) {
-            $attributes['contentHtml'] = $post->formatContent($this->request);
+            try {
+                $attributes['contentHtml'] = $post->formatContent($this->request);
+                $attributes['renderFailed'] = false;
+            } catch (Exception $e) {
+                $attributes['contentHtml'] = resolve(TranslatorInterface::class)->trans('core.lib.error.render_failed_message');
+                resolve(LogReporter::class)->report($e);
+                $attributes['renderFailed'] = true;
+            }
         } else {
             $attributes['content'] = $post->content;
         }