(dev/core#174) Update top-level interfaces to show PSR-16 support

CRM/Utils/Cache/Interface.php

@@ -30,32 +30,14 @@
  * @package CRM
  * @copyright CiviCRM LLC (c) 2004-2018
  *
- * CRM_Utils_Cache_Interface
+ * CRM_Utils_Cache_Interface is a long-standing interface used within CiviCRM
+ * for interacting with a cache service. In style and substance, it is extremely
+ * similar to PHP-FIG's SimpleCache interface (PSR-16). Consequently, beginning
+ * with CiviCRM v5.4, this extends \Psr\SimpleCache\CacheInterface.
  *
- * PHP-FIG has been developing a draft standard for caching,
- * PSR-6. The standard has not been ratified yet. When
- * making changes to this interface, please take care to
- * avoid *conflicst* with PSR-6's CacheItemPoolInterface. At
- * time of writing, they do not conflict. Avoiding conflicts
- * will enable more transition paths where Civi
- * simultaneously supports both interfaces in the same
- * implementation.
- *
- * For example, the current interface defines:
- *
- *   function get($key) => mixed $value
- *
- * and PSR-6 defines:
- *
- *   function getItem($key) => ItemInterface $item
- *
- * These are different styles (e.g. "weak item" vs "strong item"),
- * but the two methods do not *conflict*. They can coexist,
- * and you can trivially write adapters between the two.
- *
- * @see https://github.com/php-fig/fig-standards/blob/master/proposed/cache.md
+ * @see https://www.php-fig.org/psr/psr-16/
  */
-interface CRM_Utils_Cache_Interface {
+interface CRM_Utils_Cache_Interface extends \Psr\SimpleCache\CacheInterface {
 
   /**
    * Set the value in the cache.

Civi.php

@@ -26,20 +26,15 @@ class Civi {
   public static $statics = array();
 
   /**
-   * EXPERIMENTAL. Retrieve a named cache instance.
-   *
-   * This interface is flagged as experimental due to political
-   * ambiguity in PHP community -- PHP-FIG has an open but
-   * somewhat controversial draft standard for caching. Based on
-   * the current draft, it's expected that this function could
-   * simultaneously support both CRM_Utils_Cache_Interface and
-   * PSR-6, but that depends on whether PSR-6 changes any more.
+   * Retrieve a named cache instance.
    *
    * @param string $name
    *   The name of the cache. The 'default' cache is biased toward
    *   high-performance caches (eg memcache/redis/apc) when
    *   available and falls back to single-request (static) caching.
    * @return CRM_Utils_Cache_Interface
+   *   NOTE: Beginning in CiviCRM v5.4, the cache instance complies with
+   *   PSR-16 (\Psr\SimpleCache\CacheInterface).
    */
   public static function cache($name = 'default') {
     return \Civi\Core\Container::singleton()->get('cache.' . $name);