Add deprecated "user" filter for posts

In the filterer refactor for ListPostsController, the filter key was changed to `author` for consistency with the AuthorFilterGambit used in discussions. This commit adds a deprecated `user` filter back in for a release to allow for a graceful transition

src/Filter/FilterServiceProvider.php

@@ -46,6 +46,7 @@ public function register()
                     PostFilter\IdFilter::class,
                     PostFilter\NumberFilter::class,
                     PostFilter\TypeFilter::class,
+                    PostFilter\UserFilter::class,
                 ],
             ];
         });

src/Post/Filter/UserFilter.php

@@ -0,0 +1,21 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Post\Filter;
+
+/**
+ * @deprecated beta 16, remove beta 17. Use AuthorFilter instead.
+ */
+class UserFilter extends AuthorFilter
+{
+    public function getFilterKey(): string
+    {
+        return 'user';
+    }
+}

tests/integration/api/posts/ListTest.php

@@ -114,6 +114,44 @@ public function author_filter_works_with_multiple_values()
         $this->assertEquals(['1', '2', '3', '4', '5'], Arr::pluck($data['data'], 'id'));
     }
 
+    /**
+     * @test
+     * @deprecated
+     */
+    public function user_filter_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/posts', ['authenticatedAs' => 1])
+                ->withQueryParams([
+                    'filter' => ['user' => 'admin'],
+                ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true);
+
+        $this->assertEquals(['1', '2'], Arr::pluck($data['data'], 'id'));
+    }
+
+    /**
+     * @test
+     * @deprecated
+     */
+    public function user_filter_works_with_multiple_values()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/posts', ['authenticatedAs' => 1])
+                ->withQueryParams([
+                    'filter' => ['user' => 'admin,normal'],
+                ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true);
+
+        $this->assertEquals(['1', '2', '3', '4', '5'], Arr::pluck($data['data'], 'id'));
+    }
+
     /**
      * @test
      */