Merged in feature/from-pantheon (pull request #16)

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo/src/values/indexables/indexable-builder-versions.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Yoast\WP\SEO\Values\Indexables;
+
+/**
+ * Class Indexable_Builder_Versions
+ */
+class Indexable_Builder_Versions {
+
+	const DEFAULT_INDEXABLE_BUILDER_VERSION = 1;
+
+	/**
+	 * The list of indexable builder versions defined by Yoast SEO Free.
+	 * If the key is not in this list, the indexable type will not be managed.
+	 * These numbers should be increased if one of the builders implements a new feature.
+	 *
+	 * @var array
+	 */
+	protected $indexable_builder_versions_by_type = [
+		'date-archive'      => self::DEFAULT_INDEXABLE_BUILDER_VERSION,
+		'general'           => self::DEFAULT_INDEXABLE_BUILDER_VERSION,
+		'home-page'         => 2,
+		'post'              => 2,
+		'post-type-archive' => 2,
+		'term'              => 2,
+		'user'              => 2,
+		'system-page'       => self::DEFAULT_INDEXABLE_BUILDER_VERSION,
+	];
+
+	/**
+	 * Provides the most recent version number for an Indexable's object type.
+	 *
+	 * @param string $object_type The Indexable type for which you want to know the most recent version.
+	 *
+	 * @return int The most recent version number for the type, or 1 if the version doesn't exist.
+	 */
+	public function get_latest_version_for_type( $object_type ) {
+		if ( ! \array_key_exists( $object_type, $this->indexable_builder_versions_by_type ) ) {
+			return self::DEFAULT_INDEXABLE_BUILDER_VERSION;
+		}
+
+		return $this->indexable_builder_versions_by_type[ $object_type ];
+	}
+}