Slug Driver Support (#2456)

- Support slug drivers for core's sluggable models, easily extends to other models
- Add automated testing for affected single-model API routes
- Fix nickname selection UI
- Serialize slugs as `slug` attribute
- Make min search length a constant

tests/integration/extenders/ModelUrlTest.php

@@ -0,0 +1,82 @@
+<?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\Tests\integration\extenders;
+
+use Flarum\Database\AbstractModel;
+use Flarum\Extend;
+use Flarum\Http\SlugDriverInterface;
+use Flarum\Http\SlugManager;
+use Flarum\Tests\integration\RetrievesAuthorizedUsers;
+use Flarum\Tests\integration\TestCase;
+use Flarum\User\User;
+
+class ModelUrlTest extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+
+    protected function prepDb()
+    {
+        $userClass = User::class;
+        $this->prepareDatabase([
+            'users' => [
+                $this->adminUser(),
+                $this->normalUser(),
+            ],
+            'settings' => [
+                ['key' => "slug_driver_$userClass", 'value' => 'testDriver'],
+            ]
+        ]);
+    }
+
+    /**
+     * @test
+     */
+    public function uses_default_driver_by_default()
+    {
+        $this->prepDb();
+
+        $slugManager = $this->app()->getContainer()->make(SlugManager::class);
+
+        $testUser = User::find(1);
+
+        $this->assertEquals('admin', $slugManager->forResource(User::class)->toSlug($testUser));
+        $this->assertEquals('1', $slugManager->forResource(User::class)->fromSlug('admin', $testUser)->id);
+    }
+
+    /**
+     * @test
+     */
+    public function custom_slug_driver_has_effect_if_added()
+    {
+        $this->extend((new Extend\ModelUrl(User::class))->addSlugDriver('testDriver', TestSlugDriver::class));
+
+        $this->prepDb();
+
+        $slugManager = $this->app()->getContainer()->make(SlugManager::class);
+
+        $testUser = User::find(1);
+
+        $this->assertEquals('test-slug', $slugManager->forResource(User::class)->toSlug($testUser));
+        $this->assertEquals('1', $slugManager->forResource(User::class)->fromSlug('random-gibberish', $testUser)->id);
+    }
+}
+
+class TestSlugDriver implements SlugDriverInterface
+{
+    public function toSlug(AbstractModel $instance): string
+    {
+        return 'test-slug';
+    }
+
+    public function fromSlug(string $slug, User $actor): AbstractModel
+    {
+        return User::find(1);
+    }
+}