[11.x] Allow RouteServiceProvider to be loaded more than once

src/Illuminate/Foundation/Configuration/ApplicationBuilder.php

@@ -130,7 +130,7 @@ public function withRouting(?Closure $using = null,
         AppRouteServiceProvider::loadRoutesUsing($using);
 
         $this->app->booting(function () {
-            $this->app->register(AppRouteServiceProvider::class);
+            $this->app->register(AppRouteServiceProvider::class, force: true);
         });
 
         if (is_string($commands) && realpath($commands) !== false) {

src/Illuminate/Foundation/Support/Providers/RouteServiceProvider.php

@@ -90,7 +90,7 @@ protected function routes(Closure $routesCallback)
      */
     public static function loadRoutesUsing(Closure $routesCallback)
     {
-        static::$alwaysLoadRoutesUsing = $routesCallback;
+        self::$alwaysLoadRoutesUsing = $routesCallback;
     }
 
     /**
@@ -134,9 +134,11 @@ protected function loadCachedRoutes()
      */
     protected function loadRoutes()
     {
-        if (! is_null(static::$alwaysLoadRoutesUsing)) {
-            $this->app->call(static::$alwaysLoadRoutesUsing);
-        } elseif (! is_null($this->loadRoutesUsing)) {
+        if (! is_null(self::$alwaysLoadRoutesUsing)) {
+            $this->app->call(self::$alwaysLoadRoutesUsing);
+        }
+
+        if (! is_null($this->loadRoutesUsing)) {
             $this->app->call($this->loadRoutesUsing);
         } elseif (method_exists($this, 'map')) {
             $this->app->call([$this, 'map']);

tests/Integration/Foundation/Support/Providers/RouteServiceProviderTest.php

@@ -0,0 +1,75 @@
+<?php
+
+namespace Illuminate\Tests\Integration\Foundation\Support\Providers;
+
+use Illuminate\Foundation\Application;
+use Illuminate\Foundation\Configuration\Exceptions;
+use Illuminate\Foundation\Configuration\Middleware;
+use Illuminate\Foundation\Support\Providers\RouteServiceProvider;
+use Illuminate\Support\Facades\Route;
+use Illuminate\Testing\Assert;
+use Orchestra\Testbench\TestCase;
+
+class RouteServiceProviderTest extends TestCase
+{
+    /**
+     * Resolve application implementation.
+     *
+     * @return \Illuminate\Foundation\Application
+     */
+    protected function resolveApplication()
+    {
+        return Application::configure(static::applicationBasePath())
+            ->withProviders([
+                AppRouteServiceProvider::class,
+            ])
+            ->withRouting(
+                using: function () {
+                    Route::get('login', fn () => 'Login')->name('login');
+                }
+            )
+            ->withMiddleware(function (Middleware $middleware) {
+                //
+            })
+            ->withExceptions(function (Exceptions $exceptions) {
+                //
+            })->create();
+    }
+
+    public function test_it_can_register_multiple_route_service_providers()
+    {
+        Assert::assertArraySubset([
+            RouteServiceProvider::class => true,
+            AppRouteServiceProvider::class => true,
+        ], $this->app->getLoadedProviders());
+    }
+
+    public function test_it_can_uses_routes_registered_using_bootstrap_file()
+    {
+        $this->get(route('login'))
+            ->assertOk()
+            ->assertSee('Login');
+    }
+
+    public function test_it_can_uses_routes_registered_using_configuration_file()
+    {
+        $this->get(route('dashboard'))
+            ->assertOk()
+            ->assertSee('Hello');
+    }
+}
+
+class AppRouteServiceProvider extends RouteServiceProvider
+{
+    /**
+     * Bootstrap any application services.
+     *
+     * @return void
+     */
+    public function boot()
+    {
+        $this->routes(function () {
+            Route::get('dashboard', fn () => 'Hello')->name('dashboard');
+        });
+    }
+}