[9.x] Allow enum route bindings to have default values (#44255)

* Allow enum route bindings to have default values

* Attempt for compatability with PHP <8.1

* Fix for StyleCI

* Make $isEnum statement nicer

Author: Florian Stascheck

src/Illuminate/Routing/RouteDependencyResolverTrait.php

@@ -4,6 +4,7 @@
 
 use Illuminate\Support\Arr;
 use Illuminate\Support\Reflector;
+use ReflectionClass;
 use ReflectionFunctionAbstract;
 use ReflectionMethod;
 use ReflectionParameter;
@@ -77,7 +78,11 @@ protected function transformDependency(ReflectionParameter $parameter, $paramete
         // the list of parameters. If it is we will just skip it as it is probably a model
         // binding and we do not want to mess with those; otherwise, we resolve it here.
         if ($className && ! $this->alreadyInParameters($className, $parameters)) {
-            return $parameter->isDefaultValueAvailable() ? null : $this->container->make($className);
+            $isEnum = method_exists(ReflectionClass::class, 'isEnum') && (new ReflectionClass($className))->isEnum();
+
+            return $parameter->isDefaultValueAvailable()
+                ? ($isEnum ? $parameter->getDefaultValue() : null)
+                : $this->container->make($className);
         }
 
         return $skippableValue;

tests/Integration/Routing/ImplicitBackedEnumRouteBindingTest.php

@@ -24,6 +24,10 @@ public function testWithRouteCachingEnabled()
 Route::get('/categories/{category}', function (CategoryBackedEnum \$category) {
     return \$category->value;
 })->middleware('web');
+
+Route::get('/categories-default/{category?}', function (CategoryBackedEnum \$category = CategoryBackedEnum::Fruits) {
+    return \$category->value;
+})->middleware('web');
 PHP);
 
         $response = $this->get('/categories/fruits');
@@ -34,6 +38,15 @@ public function testWithRouteCachingEnabled()
 
         $response = $this->get('/categories/cars');
         $response->assertNotFound(404);
+
+        $response = $this->get('/categories-default/');
+        $response->assertSee('fruits');
+
+        $response = $this->get('/categories-default/people');
+        $response->assertSee('people');
+
+        $response = $this->get('/categories-default/fruits');
+        $response->assertSee('fruits');
     }
 
     public function testWithoutRouteCachingEnabled()
@@ -44,6 +57,10 @@ public function testWithoutRouteCachingEnabled()
             return $category->value;
         })->middleware(['web']);
 
+        Route::post('/categories-default/{category?}', function (CategoryBackedEnum $category = CategoryBackedEnum::Fruits) {
+            return $category->value;
+        })->middleware('web');
+
         $response = $this->post('/categories/fruits');
         $response->assertSee('fruits');
 
@@ -52,5 +69,14 @@ public function testWithoutRouteCachingEnabled()
 
         $response = $this->post('/categories/cars');
         $response->assertNotFound(404);
+
+        $response = $this->post('/categories-default/');
+        $response->assertSee('fruits');
+
+        $response = $this->post('/categories-default/people');
+        $response->assertSee('people');
+
+        $response = $this->post('/categories-default/fruits');
+        $response->assertSee('fruits');
     }
 }

tests/Routing/ImplicitRouteBindingTest.php

@@ -36,6 +36,21 @@ public function test_it_can_resolve_the_implicit_backed_enum_route_bindings_for_
         $this->assertSame('fruits', $route->parameter('category')->value);
     }
 
+    /**
+     * @requires PHP >= 8.1
+     */
+    public function test_it_can_resolve_the_backed_enum_default_value_for_the_given_route()
+    {
+        $action = ['uses' => function (CategoryBackedEnum $category = CategoryBackedEnum::Fruits) {
+            return $category->value;
+        }];
+
+        $route = new Route('GET', '/test', $action);
+        $route->parameters = [];
+
+        $this->assertSame('fruits', $route->run());
+    }
+
     /**
      * @requires PHP >= 8.1
      */