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

src/Http/HttpServiceProvider.php

@@ -9,7 +9,13 @@
 
 namespace Flarum\Http;
 
+use Flarum\Discussion\Discussion;
+use Flarum\Discussion\IdWithTransliteratedSlugDriver;
 use Flarum\Foundation\AbstractServiceProvider;
+use Flarum\Settings\SettingsRepositoryInterface;
+use Flarum\User\User;
+use Flarum\User\UsernameSlugDriver;
+use Illuminate\Support\Arr;
 
 class HttpServiceProvider extends AbstractServiceProvider
 {
@@ -25,5 +31,35 @@ class HttpServiceProvider extends AbstractServiceProvider
         $this->app->bind(Middleware\CheckCsrfToken::class, function ($app) {
             return new Middleware\CheckCsrfToken($app->make('flarum.http.csrfExemptPaths'));
         });
+
+        $this->app->singleton('flarum.http.slugDrivers', function () {
+            return [
+                Discussion::class => [
+                    'default' => IdWithTransliteratedSlugDriver::class
+                ],
+                User::class => [
+                    'default' => UsernameSlugDriver::class
+                ],
+            ];
+        });
+
+        $this->app->singleton('flarum.http.selectedSlugDrivers', function () {
+            $settings = $this->app->make(SettingsRepositoryInterface::class);
+
+            $compiledDrivers = [];
+
+            foreach ($this->app->make('flarum.http.slugDrivers') as $resourceClass => $resourceDrivers) {
+                $driverKey = $settings->get("slug_driver_$resourceClass", 'default');
+
+                $driverClass = Arr::get($resourceDrivers, $driverKey, $resourceDrivers['default']);
+
+                $compiledDrivers[$resourceClass] = $this->app->make($driverClass);
+            }
+
+            return $compiledDrivers;
+        });
+        $this->app->bind(SlugManager::class, function () {
+            return new SlugManager($this->app->make('flarum.http.selectedSlugDrivers'));
+        });
     }
 }