From d2900abc52256190275b1ed7c3d75e88d14c48c4 Mon Sep 17 00:00:00 2001
From: David Rothstein <drothstein@gmail.com>
Date: Mon, 12 Oct 2015 14:19:06 -0400
Subject: Issue #1534490 by msonnabaum, bigjim, David_Rothstein, pounard, Dave
 Reid: Make block cache cids alterable

---
 CHANGELOG.txt               |  2 ++
 modules/block/block.api.php | 25 +++++++++++++++++++++++++
 modules/block/block.module  |  1 +
 3 files changed, 28 insertions(+)

diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index 98f4bca25..dfdfdd765 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -1,6 +1,8 @@
 
 Drupal 7.40, xxxx-xx-xx (development version)
 -----------------------
+- Added a new hook, hook_block_cid_parts_alter(), to allow modules to alter the
+  cache keys used for caching a particular block.
 - Made drupal_set_message() display and return messages when "0" is passed in
   as the message to set.
 - Fixed non-functional "Files displayed by default" setting on file fields.
diff --git a/modules/block/block.api.php b/modules/block/block.api.php
index d7453b24b..e38f7d6ee 100644
--- a/modules/block/block.api.php
+++ b/modules/block/block.api.php
@@ -363,6 +363,31 @@ function hook_block_list_alter(&$blocks) {
   }
 }
 
+/**
+ * Act on block cache ID (cid) parts before the cid is generated.
+ *
+ * This hook allows you to add, remove or modify the custom keys used to
+ * generate a block cache ID (by default, these keys are set to the block
+ * module and delta). These keys will be combined with the standard ones
+ * provided by drupal_render_cid_parts() to generate the final block cache ID.
+ *
+ * To change the cache granularity used by drupal_render_cid_parts(), this hook
+ * cannot be used; instead, set the 'cache' key in the block's definition in
+ * hook_block_info().
+ *
+ * @params $cid_parts
+ *   An array of elements used to build the cid.
+ * @param $block
+ *   The block object being acted on.
+ *
+ * @see _block_get_cache_id()
+ */
+function hook_block_cid_parts_alter(&$cid_parts, $block) {
+  global $user;
+  // This example shows how to cache a block based on the user's timezone.
+  $cid_parts[] = $user->timezone;
+}
+
 /**
  * @} End of "addtogroup hooks".
  */
diff --git a/modules/block/block.module b/modules/block/block.module
index 48c80d766..fe04e9902 100644
--- a/modules/block/block.module
+++ b/modules/block/block.module
@@ -967,6 +967,7 @@ function _block_get_cache_id($block) {
     // Start with common sub-patterns: block identification, theme, language.
     $cid_parts[] = $block->module;
     $cid_parts[] = $block->delta;
+    drupal_alter('block_cid_parts', $cid_parts, $block);
     $cid_parts = array_merge($cid_parts, drupal_render_cid_parts($block->cache));
 
     return implode(':', $cid_parts);
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