diff -u b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
--- b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -8,11 +8,12 @@
 namespace Drupal\Core\Plugin\Discovery;
 
 use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
+use Drupal\Component\Reflection\MockFileFinder;
 use Drupal\Core\Annotation\DirectoryIterator;
+use Drupal\Core\Annotation\Plugin;
 use Doctrine\Common\Annotations\AnnotationReader;
 use Doctrine\Common\Annotations\AnnotationRegistry;
 use Doctrine\Common\Reflection\StaticReflectionParser;
-use Drupal\Core\Annotation\Plugin;
 
 /**
  * A discovery mechanism finds annotated plugins in PSR-0 namespaces.
@@ -53,12 +54,14 @@
           $directories = new DirectoryIterator($dir);
           foreach ($directories as $fileinfo) {
             if ($fileinfo->getExtension() == 'php') {
-              $className = str_replace(DIRECTORY_SEPARATOR, '\\', "$prefix/". $fileinfo->getBasename('.php'));
-              $finder = DumbFindFile::create($fileinfo->getPathName());
-              $staticReflectionParser = new StaticReflectionParser($className, $finder);
-              if ($annotation = $reader->getClassAnnotation($staticReflectionParser->getReflectionClass(), 'Drupal\Core\Annotation\Plugin')) {
+              $class = str_replace(DIRECTORY_SEPARATOR, '\\', "$prefix/". $fileinfo->getBasename('.php'));
+              // The file name is already known so no need to find the file,
+              // but StaticReflectionParser needs one so use a mock version.
+              $finder = MockFileFinder::create($fileinfo->getPathName());
+              $parser = new StaticReflectionParser($class, $finder);
+              if ($annotation = $reader->getClassAnnotation($parser->getReflectionClass(), 'Drupal\Core\Annotation\Plugin')) {
                 $definition = $annotation->get();
-                $definition['class'] = $className;
+                $definition['class'] = $class;
                 $definitions[$definition['plugin_id']] = $definition;
               }
             }
reverted:
--- b/core/lib/Drupal/Core/Plugin/Discovery/DumbFindFile.php
+++ /dev/null
@@ -1,37 +0,0 @@
-<?php
-
-/**
- * Definition of Drupal\Core\Plugin\Discovery\DumbFindFile.
- */
-
-namespace Drupal\Core\Plugin\Discovery;
-
-use Doctrine\Common\Reflection\ClassFinderInterface;
-
-/**
- * This is a dumb file finder: only returns a single filename.
- */
-class DumbFindFile implements ClassFinderInterface {
-
-  /**
-   * The only filename this finder ever returns.
-   */
-  protected $filename;
-
-  public function __construct($prefixes) {
-  }
-
-  public function hint($filename) {
-    $this->filename = $filename;
-    return $this;
-  }
-
-  public function findFile($class) {
-    return $this->filename;
-  }
-
-  static public function create($filename) {
-    $dumbFindFile = new DumbFindFile(array());
-    return $dumbFindFile->hint($filename);
-  }
-}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/lib/Drupal/Component/Reflection/MockFileFinder.php
@@ -0,0 +1,47 @@
+<?php
+
+/**
+ * Definition of Drupal\Core\Plugin\Discovery\DumbFindFile.
+ */
+
+namespace Drupal\Component\Reflection;
+
+use Doctrine\Common\Reflection\ClassFinderInterface;
+
+/**
+ * This is a dumb file finder: only returns a single filename.
+ *
+ * It can be used with \Doctrine\Common\Reflection\StaticReflectionParser if
+ * the filename is known and inheritance is not a concern (for example, if
+ * only the class annotation is needed).
+ */
+class MockFileFinder implements ClassFinderInterface {
+
+  /**
+   * The only filename this finder ever returns.
+   */
+  protected $filename;
+
+  /**
+   * Implements \Doctrine\Common\Reflection\ClassFinderInterface::__construct().
+   */
+  public function __construct($prefixes) {
+  }
+
+  /**
+   * Implements \Doctrine\Common\Reflection\ClassFinderInterface::findFile().
+   */
+  public function findFile($class) {
+    return $this->filename;
+  }
+
+
+  /**
+   * Factory for the mock file finder.
+   */
+  static public function create($filename) {
+    $object = new static(array());
+    $object->filename = $filename;
+    return $object;
+  }
+}