Improve some post/discussion permission logic

- Allow users to see their own posts, even if they have been hidden by
someone else
- Don't require hiding a post to be necessarily attributed to a user
- Hide discussions with zero posts, unless the user can edit posts, or
they are the discussion author

src/Core/Discussions/DiscussionsServiceProvider.php

@@ -13,7 +13,9 @@ namespace Flarum\Core\Discussions;
 use Flarum\Core\Search\GambitManager;
 use Flarum\Core\Users\User;
 use Flarum\Events\ModelAllow;
+use Flarum\Events\ScopeModelVisibility;
 use Flarum\Events\RegisterDiscussionGambits;
+use Flarum\Events\ScopeEmptyDiscussionVisibility;
 use Flarum\Support\ServiceProvider;
 use Flarum\Extend;
 use Illuminate\Contracts\Container\Container;
@@ -53,6 +55,19 @@ class DiscussionsServiceProvider extends ServiceProvider
                 }
             }
         });
+
+        $events->listen(ScopeModelVisibility::class, function (ScopeModelVisibility $event) {
+            if ($event->model instanceof Discussion) {
+                if (! $event->actor->hasPermission('discussion.editPosts')) {
+                    $event->query->where(function ($query) use ($event) {
+                        $query->where('comments_count', '>', '0')
+                            ->orWhere('start_user_id', $event->actor->id);
+
+                        event(new ScopeEmptyDiscussionVisibility($query, $event->actor));
+                    });
+                }
+            }
+        });
     }
 
     /**

src/Core/Posts/CommentPost.php

@@ -87,7 +87,7 @@ class CommentPost extends Post
      * @param User $actor
      * @return $this
      */
-    public function hide(User $actor)
+    public function hide(User $actor = null)
     {
         if ($this->number == 1) {
             throw new DomainException('Cannot hide the first post of a discussion');
@@ -95,7 +95,7 @@ class CommentPost extends Post
 
         if (! $this->hide_time) {
             $this->hide_time = time();
-            $this->hide_user_id = $actor->id;
+            $this->hide_user_id = $actor ? $actor->id : null;
 
             $this->raise(new PostWasHidden($this));
         }

src/Core/Posts/PostsServiceProvider.php

@@ -44,7 +44,7 @@ class PostsServiceProvider extends ServiceProvider
                 $actor = $event->actor;
 
                 if ($action === 'view' &&
-                    (! $post->hide_user_id || $post->hide_user_id == $actor->id || $post->can($actor, 'edit'))) {
+                    (! $post->hide_time || $post->user_id == $actor->id || $post->can($actor, 'edit'))) {
                     return true;
                 }
 
@@ -55,7 +55,7 @@ class PostsServiceProvider extends ServiceProvider
                     if ($post->discussion->can($actor, 'editPosts')) {
                         return true;
                     }
-                    if ($post->user_id == $actor->id && (! $post->hide_user_id || $post->hide_user_id == $actor->id)) {
+                    if ($post->user_id == $actor->id && (! $post->hide_time || $post->hide_user_id == $actor->id)) {
                         $allowEditing = $settings->get('allow_post_editing');
 
                         if ($allowEditing === '-1' ||
@@ -80,8 +80,8 @@ class PostsServiceProvider extends ServiceProvider
 
             if (! $event->discussion->can($user, 'editPosts')) {
                 $event->query->where(function ($query) use ($user) {
-                    $query->whereNull('hide_user_id')
-                        ->orWhere('hide_user_id', $user->id);
+                    $query->whereNull('hide_time')
+                        ->orWhere('user_id', $user->id);
                 });
             }
         });

src/Events/ScopeEmptyDiscussionVisibility.php

@@ -0,0 +1,40 @@
+<?php
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Events;
+
+use Flarum\Core\Users\User;
+use Illuminate\Database\Eloquent\Builder;
+
+/**
+ * The `ScopeEmptyDiscussionVisibility` event
+ */
+class ScopeEmptyDiscussionVisibility
+{
+    /**
+     * @var Builder
+     */
+    public $query;
+
+    /**
+     * @var User
+     */
+    public $actor;
+
+    /**
+     * @param Builder $query
+     * @param User $actor
+     */
+    public function __construct(Builder $query, User $actor)
+    {
+        $this->query = $query;
+        $this->actor = $actor;
+    }
+}