Only get posts with registered types.

This is so that if an extension adds a post type, and the database gets
populated with posts of that type, but then if the extension is
disabled, we wouldn’t want those posts to display because we would have
no knowledge about how to deal with/render them.

src/Core/Models/Discussion.php

@@ -68,7 +68,7 @@ class Discussion extends Model
         static::deleted(function ($discussion) {
             $discussion->raise(new DiscussionWasDeleted($discussion));
 
-            $discussion->posts()->delete();
+            $discussion->posts()->allTypes()->delete();
             $discussion->readers()->detach();
         });
     }

src/Core/Models/Post.php

@@ -65,6 +65,8 @@ class Post extends Model
         static::deleted(function ($post) {
             $post->raise(new PostWasDeleted($post));
         });
+
+        static::addGlobalScope(new RegisteredTypesScope);
     }
 
     /**
@@ -119,6 +121,18 @@ class Post extends Model
         return array_map('intval', $query->get(['id'])->fetch('id')->all());
     }
 
+    /**
+     * Get all posts, regardless of their type, by removing the
+     * `RegisteredTypesScope` global scope constraints applied on this model.
+     *
+     * @param \Illuminate\Database\Eloquent\Builder $query
+     * @return \Illuminate\Database\Eloquent\Builder
+     */
+    public function scopeAllTypes($query)
+    {
+        return $this->removeGlobalScopes($query);
+    }
+
     /**
      * Create a new model instance according to the post's type.
      *
@@ -155,4 +169,9 @@ class Post extends Model
     {
         static::$types[$type] = $class;
     }
+
+    public static function getTypes()
+    {
+        return static::$types;
+    }
 }

src/Core/Models/RegisteredTypesScope.php

@@ -0,0 +1,55 @@
+<?php namespace Flarum\Core\Models;
+
+use Illuminate\Database\Eloquent\ScopeInterface;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Model;
+
+class RegisteredTypesScope implements ScopeInterface
+{
+    /**
+     * Apply the scope to a given Eloquent query builder.
+     *
+     * @param  \Illuminate\Database\Eloquent\Builder  $builder
+     * @param  \Illuminate\Database\Eloquent\Model  $model
+     * @return void
+     */
+    public function apply(Builder $builder, Model $model)
+    {
+        $builder->whereIn('type', array_keys($model::getTypes()));
+    }
+
+    /**
+     * Remove the scope from the given Eloquent query builder.
+     *
+     * @param  \Illuminate\Database\Eloquent\Builder  $builder
+     * @param  \Illuminate\Database\Eloquent\Model  $model
+     * @return void
+     */
+    public function remove(Builder $builder, Model $model)
+    {
+        $query = $builder->getQuery();
+
+        foreach ((array) $query->wheres as $key => $where)
+        {
+            if ($this->isTypeConstraint($where))
+            {
+                unset($query->wheres[$key]);
+
+                $query->wheres = array_values($query->wheres);
+            }
+        }
+    }
+
+    /**
+     * Determine if the given where clause is a type constraint.
+     *
+     * @param  array   $where
+     * @param  string  $column
+     * @return bool
+     */
+    protected function isTypeConstraint(array $where)
+    {
+        return $where['type'] == 'In' && $where['column'] == 'type';
+    }
+
+}