fix: controller filter attribute docs and improve invalid attribute logging

system/Router/Router.php

@@ -803,8 +803,8 @@ private function processRouteAttributes(): void
                 if ($instance instanceof RouteAttributeInterface) {
                     $this->routeAttributes['class'][] = $instance;
                 }
-            } catch (Throwable) {
-                log_message('error', 'Failed to instantiate attribute: ' . $attribute->getName());
+            } catch (Throwable $e) {
+                $this->logRouteAttributeInstantiationFailure($attribute->getName(), $this->controller, null, $e);
             }
         }
 
@@ -823,14 +823,43 @@ private function processRouteAttributes(): void
                     if ($instance instanceof RouteAttributeInterface) {
                         $this->routeAttributes['method'][] = $instance;
                     }
-                } catch (Throwable) {
-                    // Skip attributes that fail to instantiate
-                    log_message('error', 'Failed to instantiate attribute: ' . $attribute->getName());
+                } catch (Throwable $e) {
+                    $this->logRouteAttributeInstantiationFailure($attribute->getName(), $this->controller, $this->method, $e);
                 }
             }
         }
     }
 
+    /**
+     * Logs an attribute instantiation failure with the resolved route context.
+     *
+     * @param string      $attributeName Fully qualified attribute class name.
+     * @param string      $controller    Resolved controller class name.
+     * @param string|null $method        Resolved controller method name, if applicable.
+     */
+    private function logRouteAttributeInstantiationFailure(
+        string $attributeName,
+        string $controller,
+        ?string $method,
+        Throwable $e,
+    ): void {
+        $location = $controller;
+
+        if ($method !== null && $method !== '') {
+            $location .= '::' . $method . '()';
+        }
+
+        log_message(
+            'error',
+            'Failed to instantiate route attribute "{attribute}" on "{location}": {message}',
+            [
+                'attribute' => $attributeName,
+                'location'  => $location,
+                'message'   => $e->getMessage(),
+            ],
+        );
+    }
+
     /**
      * Execute beforeController() on all route attributes.
      * Called by CodeIgniter before controller execution.

tests/_support/Router/Controllers/InvalidAttributeController.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace Tests\Support\Router\Controllers;
+
+use CodeIgniter\Controller;
+use CodeIgniter\HTTP\ResponseInterface;
+use CodeIgniter\Router\Attributes\Filter;
+
+class InvalidAttributeController extends Controller
+{
+    #[Filter(by: ['auth', 'csrf'])]
+    public function invalidMultipleFilters(): ResponseInterface
+    {
+        return $this->response->setBody('Invalid attributes');
+    }
+}

tests/system/Router/RouterTest.php

@@ -20,6 +20,7 @@
 use CodeIgniter\HTTP\Exceptions\RedirectException;
 use CodeIgniter\HTTP\IncomingRequest;
 use CodeIgniter\HTTP\Method;
+use CodeIgniter\Router\Attributes\Filter;
 use CodeIgniter\Router\Exceptions\RouterException;
 use CodeIgniter\Test\CIUnitTestCase;
 use Config\App;
@@ -29,6 +30,7 @@
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\Attributes\Group;
 use Tests\Support\Filters\Customfilter;
+use Tests\Support\Router\Controllers\InvalidAttributeController;
 
 /**
  * @internal
@@ -1003,4 +1005,27 @@ public function testRoutePlaceholderAnyWithMultipleSegmentsParamTrue(): void
         $this->assertSame('productLookup', $router->methodName());
         $this->assertSame(['123/456'], $router->params());
     }
+
+    public function testLogsRouteAttributeInstantiationFailureWithContext(): void
+    {
+        $collection = clone $this->collection;
+        $collection->resetRoutes();
+        $collection->get(
+            'invalid-attribute',
+            'Tests\Support\Router\Controllers\InvalidAttributeController::invalidMultipleFilters',
+        );
+
+        $router = new Router($collection, $this->request);
+
+        $router->handle('invalid-attribute');
+
+        $this->assertSame(
+            '\\' . InvalidAttributeController::class,
+            $router->controllerName(),
+        );
+        $this->assertSame('invalidMultipleFilters', $router->methodName());
+        $this->assertSame([], $router->getFilters());
+        $this->assertLogContains('error', 'Failed to instantiate route attribute "' . Filter::class . '" on "\Tests\Support\Router\Controllers\InvalidAttributeController::invalidMultipleFilters()":');
+        $this->assertLogContains('error', 'must be of type string');
+    }
 }

user_guide_src/source/incoming/controller_attributes/003.php

@@ -18,8 +18,9 @@ public function api()
     {
     }
 
-    // Multiple filters can be applied
-    #[Filter(by: ['auth', 'csrf'])]
+    // Multiple filters can be applied by repeating the attribute
+    #[Filter(by: 'auth')]
+    #[Filter(by: 'csrf')]
     public function admin()
     {
     }