diff --git a/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php b/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php
index 8cf45a1..fa3bafb 100644
--- a/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php
+++ b/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php
@@ -20,7 +20,7 @@ class YamlDirectoryDiscovery implements DiscoverableInterface {
   /**
    * Defines the key in the discovered data where the file path is stored.
    */
-  const DISCOVERY_PATH = '_discovery_path';
+  const FILE_KEY = '_discovered_file_path';
 
   /**
    * An array of directories to scan, keyed by the provider.
@@ -44,7 +44,7 @@ class YamlDirectoryDiscovery implements DiscoverableInterface {
    *
    * @var string
    */
-  protected $key;
+  protected $idKey;
 
   /**
    * Constructs a YamlDirectoryDiscovery object.
@@ -61,7 +61,7 @@ class YamlDirectoryDiscovery implements DiscoverableInterface {
   public function __construct(array $directories, $file_cache_key_suffix, $key = 'id') {
     $this->directories = $directories;
     $this->fileCacheKeySuffix = $file_cache_key_suffix;
-    $this->key = $key;
+    $this->idKey = $key;
   }
 
   /**
@@ -92,7 +92,7 @@ public function findAll() {
         catch (InvalidDataTypeException $e) {
           throw new DiscoveryException("The $file contains invalid YAML", 0, $e);
         }
-        $data[static::DISCOVERY_PATH] = $file;
+        $data[static::FILE_KEY] = $file;
         $all[$provider][$this->getIdentifier($file, $data)] = $data;
         $file_cache->set($file, $data);
       }
@@ -104,6 +104,8 @@ public function findAll() {
   /**
    * Gets the identifier from the data.
    *
+   * @param string $file
+   *   The filename.
    * @param array $data
    *   The data from the YAML file.
    *
@@ -111,10 +113,10 @@ public function findAll() {
    *   The identifier from the data.
    */
   protected function getIdentifier($file, array $data) {
-    if (!isset($data[$this->key])) {
-      throw new DiscoveryException("The $file contains no data in the identifier key '{$this->key}'");
+    if (!isset($data[$this->idKey])) {
+      throw new DiscoveryException("The $file contains no data in the identifier key '{$this->idKey}'");
     }
-    return $data[$this->key];
+    return $data[$this->idKey];
   }
 
   /**
@@ -146,7 +148,7 @@ protected function findFiles() {
    * a class that extends this one. For example, it could be used to make the
    * scan recursive.
    *
-   * @param $directory
+   * @param string $directory
    *   The directory to scan.
    *
    * @return \Traversable
diff --git a/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php b/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php
index 0289e5f..3e46605 100644
--- a/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php
+++ b/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php
@@ -76,18 +76,18 @@ public function testDiscovery() {
     $discovery = new YamlDirectoryDiscovery($directories, 'test');
     $data = $discovery->findAll();
 
-    $this->assertSame(['id' => 'item1', 'name' => 'test1 item 1', '_discovery_path' => 'vfs://modules/test_1/subdir1/item_1.test.yml'], $data['test_1']['item1']);
-    $this->assertSame(['id' => 'item2', 'name' => 'test1 item 2', '_discovery_path' => 'vfs://modules/test_1/subdir2/item_2.test.yml'], $data['test_1']['item2']);
+    $this->assertSame(['id' => 'item1', 'name' => 'test1 item 1', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_1/subdir1/item_1.test.yml'], $data['test_1']['item1']);
+    $this->assertSame(['id' => 'item2', 'name' => 'test1 item 2', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_1/subdir2/item_2.test.yml'], $data['test_1']['item2']);
     $this->assertCount(2, $data['test_1']);
 
-    $this->assertSame(['id' => 'item3', 'name' => 'test2 item 3', '_discovery_path' => 'vfs://modules/test_2/subdir1/item_3.test.yml'], $data['test_2']['item3']);
+    $this->assertSame(['id' => 'item3', 'name' => 'test2 item 3', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_2/subdir1/item_3.test.yml'], $data['test_2']['item3']);
     $this->assertCount(1, $data['test_2']);
 
     $this->assertTrue(empty($data['test_3']), 'test_3 provides 0 items');
 
-    $this->assertSame(['id' => 'item4', 'name' => 'test4 item 4', '_discovery_path' => 'vfs://modules/test_4/subdir1/item_4.test.yml'], $data['test_4']['item4']);
-    $this->assertSame(['id' => 'item5', 'name' => 'test4 item 5', '_discovery_path' => 'vfs://modules/test_4/subdir1/item_5.test.yml'], $data['test_4']['item5']);
-    $this->assertSame(['id' => 'item6', 'name' => 'test4 item 6', '_discovery_path' => 'vfs://modules/test_4/subdir1/item_6.test.yml'], $data['test_4']['item6']);
+    $this->assertSame(['id' => 'item4', 'name' => 'test4 item 4', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_4/subdir1/item_4.test.yml'], $data['test_4']['item4']);
+    $this->assertSame(['id' => 'item5', 'name' => 'test4 item 5', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_4/subdir1/item_5.test.yml'], $data['test_4']['item5']);
+    $this->assertSame(['id' => 'item6', 'name' => 'test4 item 6', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_4/subdir1/item_6.test.yml'], $data['test_4']['item6']);
     $this->assertCount(3, $data['test_4']);
   }
 
@@ -109,7 +109,7 @@ public function testDiscoveryAlternateId() {
     $discovery = new YamlDirectoryDiscovery($directories, 'test', 'alt_id');
     $data = $discovery->findAll();
 
-    $this->assertSame(['alt_id' => 'item1', 'id' => 'ignored', '_discovery_path' => 'vfs://modules/test_1/item_1.test.yml'], $data['test_1']['item1']);
+    $this->assertSame(['alt_id' => 'item1', 'id' => 'ignored', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_1/item_1.test.yml'], $data['test_1']['item1']);
     $this->assertCount(1, $data['test_1']);
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Plugin/Discovery/YamlDirectoryDiscoveryTest.php b/core/tests/Drupal/Tests/Core/Plugin/Discovery/YamlDirectoryDiscoveryTest.php
index f057f55..d7b2698 100644
--- a/core/tests/Drupal/Tests/Core/Plugin/Discovery/YamlDirectoryDiscoveryTest.php
+++ b/core/tests/Drupal/Tests/Core/Plugin/Discovery/YamlDirectoryDiscoveryTest.php
@@ -61,7 +61,7 @@ public function testGetDefinitions() {
     $this->assertCount(4, $definitions);
 
     foreach ($definitions as $id => $definition) {
-      foreach (array('id', 'provider', ComponentYamlDirectoryDiscovery::DISCOVERY_PATH) as $key) {
+      foreach (array('id', 'provider', ComponentYamlDirectoryDiscovery::FILE_KEY) as $key) {
         $this->assertArrayHasKey($key, $definition);
       }
       $this->assertEquals($id, $definition['id']);