--- /dev/null
+<?php
+
+namespace Drupal\Component\Discovery;
+
+use Drupal\Component\Serialization\Yaml;
+use Drupal\Component\FileCache\FileCacheFactory;
+
+/**
+ * Provides discovery for YAML files within a given set of directories.
+ */
+class YamlDiscovery implements DiscoverableInterface {
+
+ /**
+ * The base filename to look for in each directory.
+ *
+ * @var string
+ */
+ protected $name;
+
+ /**
+ * An array of directories to scan, keyed by the provider.
+ *
+ * @var array
+ */
+ protected $directories = [];
+
+ /**
+ * Constructs a YamlDiscovery object.
+ *
+ * @param string $name
+ * The base filename to look for in each directory. The format will be
+ * $provider.$name.yml.
+ * @param array $directories
+ * An array of directories to scan, keyed by the provider.
+ */
+ public function __construct($name, array $directories) {
+ $this->name = $name;
+ $this->directories = $directories;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function findAll() {
+ $all = [];
+
+ $files = $this->findFiles();
+ $provider_by_files = array_flip($files);
+
+ $file_cache = FileCacheFactory::get('yaml_discovery:' . $this->name);
+
+ // Try to load from the file cache first.
+ foreach ($file_cache->getMultiple($files) as $file => $data) {
+ $all[$provider_by_files[$file]] = $data;
+ unset($provider_by_files[$file]);
+ }
+
+ // If there are files left that were not returned from the cache, load and
+ // parse them now. This list was flipped above and is keyed by filename.
+ if ($provider_by_files) {
+ foreach ($provider_by_files as $file => $provider) {
+ // If a file is empty or its contents are commented out, return an empty
+ // array instead of NULL for type consistency.
+ $all[$provider] = $this->decode($file);
+ $file_cache->set($file, $all[$provider]);
+ }
+ }
+
+ return $all;
+ }
+
+ /**
+ * Decode a YAML file.
+ *
+ * @param string $file
+ * Yaml file path.
+ * @return array
+ */
+ protected function decode($file) {
+ return Yaml::decode(file_get_contents($file)) ?: [];
+ }
+
+ /**
+ * Returns an array of file paths, keyed by provider.
+ *
+ * @return array
+ */
+ protected function findFiles() {
+ $files = [];
+ foreach ($this->directories as $provider => $directory) {
+ $file = $directory . '/' . $provider . '.' . $this->name . '.yml';
+ if (file_exists($file)) {
+ $files[$provider] = $file;
+ }
+ }
+ return $files;
+ }
+
+}