SmartPlaceholderCache

smart-placeholder-cache-wip.diff

diff --git a/core/lib/Drupal/Core/Render/BubbleableMetadata.php b/core/lib/Drupal/Core/Render/BubbleableMetadata.php
index c56b421..748bc0b 100644
--- a/core/lib/Drupal/Core/Render/BubbleableMetadata.php
+++ b/core/lib/Drupal/Core/Render/BubbleableMetadata.php
@@ -39,6 +39,13 @@ class BubbleableMetadata {
   protected $postRenderCache;
 
   /**
+   * #placeholder metadata.
+   *
+   * @var array[]
+   */
+  protected $placeholders;
+
+  /**
    * Constructs a BubbleableMetadata value object.
    *
    * @param string[] $tags
@@ -47,9 +54,12 @@ class BubbleableMetadata {
    *   An array of attached assets.
    * @param array $post_render_cache
    *   An array of #post_render_cache metadata.
+   * @param array $placeholders
+   *   An array of #cache placeholders metadata.
    */
-  public function __construct(array $tags = [], array $attached = [], array $post_render_cache = []) {
+  public function __construct(array $tags = [], array $attached = [], array $post_render_cache = [], array $placeholders = []) {
     $this->tags = $tags;
+    $this->placeholders = $placeholders;
     $this->attached = $attached;
     $this->postRenderCache = $post_render_cache;
   }
@@ -70,6 +80,7 @@ public function __construct(array $tags = [], array $attached = [], array $post_
   public function merge(BubbleableMetadata $other) {
     $result = new BubbleableMetadata();
     $result->tags = Cache::mergeTags($this->tags, $other->tags);
+    $result->placeholders = NestedArray::mergeDeep($this->placeholders, $other->placeholders);
     $result->attached = drupal_merge_attached($this->attached, $other->attached);
     $result->postRenderCache = NestedArray::mergeDeep($this->postRenderCache, $other->postRenderCache);
     return $result;
@@ -83,6 +94,7 @@ public function merge(BubbleableMetadata $other) {
    */
   public function applyTo(array &$build) {
     $build['#cache']['tags'] = $this->tags;
+    $build['#cache']['placeholders'] = $this->placeholders;
     $build['#attached'] = $this->attached;
     $build['#post_render_cache'] = $this->postRenderCache;
   }
@@ -98,6 +110,7 @@ public function applyTo(array &$build) {
   public static function createFromRenderArray(array $build) {
     $meta = new static();
     $meta->tags = (isset($build['#cache']['tags'])) ? $build['#cache']['tags'] : [];
+    $meta->placeholders = (isset($build['#cache']['placeholders'])) ? $build['#cache']['placeholders'] : [];
     $meta->attached = (isset($build['#attached'])) ? $build['#attached'] : [];
     $meta->postRenderCache = (isset($build['#post_render_cache'])) ? $build['#post_render_cache'] : [];
     return $meta;
     diff --git a/core/lib/Drupal/Core/Render/Renderer.php b/core/lib/Drupal/Core/Render/Renderer.php
index 69e99a0..d280cab 100644
--- a/core/lib/Drupal/Core/Render/Renderer.php
+++ b/core/lib/Drupal/Core/Render/Renderer.php
@@ -64,6 +64,11 @@ class Renderer implements RendererInterface {
   protected $cacheContexts;
 
   /**
+   * The stored placeholders.
+   */
+  protected static $cachePlaceholders;
+
+  /**
    * The stack containing bubbleable rendering metadata.
    *
    * @var \SplStack|null
@@ -184,6 +189,11 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
         $this->bubbleStack();
         return $elements['#markup'];
       }
+
+      // Store the cache ID for later comparison.
+      if ($this->requestStack->getCurrentRequest()->isMethodSafe() && $cid = $this->createCacheID($elements)) {
+        $elements['#cache_old_id'] = $cid;
+      }
     }
 
     // If the default values for this element have not been loaded yet, populate
@@ -206,6 +216,7 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
 
     // Defaults for bubbleable rendering metadata.
     $elements['#cache']['tags'] = isset($elements['#cache']['tags']) ? $elements['#cache']['tags'] : array();
+    $elements['#cache']['placeholders'] = isset($elements['#cache']['placeholders']) ? $elements['#cache']['placeholders'] : array();
     $elements['#attached'] = isset($elements['#attached']) ? $elements['#attached'] : array();
     $elements['#post_render_cache'] = isset($elements['#post_render_cache']) ? $elements['#post_render_cache'] : array();
 
@@ -339,6 +350,11 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
     $suffix = isset($elements['#suffix']) ? SafeMarkup::checkAdminXss($elements['#suffix']) : '';
 
     $elements['#markup'] = $prefix . $elements['#children'] . $suffix;
+    
+    // @todo This means the root call element should not have #cache to be cached properly.
+    if ($is_root_call) {
+      $this->processPlaceholders($elements);
+    }
 
     // We've rendered this element (and its subtree!), now update the stack.
     $this->updateStack($elements);
@@ -394,6 +410,7 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
    */
   protected function resetStack() {
     static::$stack = NULL;
+    static::$cachePlaceholders = NULL;
   }
 
   /**
@@ -468,6 +485,17 @@ protected function processPostRenderCache(array &$elements) {
     }
   }
 
+  protected function processPlaceholders(array &$elements) {
+    if (isset($elements['#cache']['placeholders'])) {
+      foreach ($elements['#cache']['placeholders'] as $placeholder => $element) {
+        $data = static::$cachePlaceholders[$placeholder];
+        // This is already rendered, but we want to bubble the data up to $elements.
+        $markup = $this->doRender($data);
+        $elements['#markup'] = str_replace($placeholder, $markup, $elements['#markup']);
+      }
+    }
+  }
+
   /**
    * Gets the cached, prerendered element of a renderable element from the cache.
    *
@@ -493,12 +521,45 @@ protected function cacheGet(array $elements) {
 
     if (!empty($cid) && $cache = $this->cacheFactory->get($bin)->get($cid)) {
       $cached_element = $cache->data;
+      if (!empty($cached_element['#cache']['placeholders']) && !$this->checkPlaceholders($cached_element['#cache']['placeholders'])) {
+        return FALSE; 
+      }
+
       // Return the cached element.
       return $cached_element;
     }
     return FALSE;
   }
 
+  protected function checkPlaceholders($placeholders) {
+    $cid_map = [];
+    foreach ($placeholders as $placeholder => $elements) {
+      $cid_map[$placeholder] = $this->createCacheID($elements);
+    }
+    $cids = array_keys($cid_map);
+
+    // @todo do this per 'bin'.
+    $cached = $this->cacheFactory->get('render')->getMultiple($cids);
+
+    // A cache miss is fatal.
+    if (count($cached) != count($cid_map)) {
+      return FALSE;
+    }
+
+    $data = array();
+    // Store in this class - unless reset.
+    foreach ($cid_map as $placeholder => $cid) {
+      $cached_element = $cached[$cid]->data;
+      if (!empty($cached_element['#cache']['placeholders']) && !$this->checkPlaceholders($cached_element['#cache']['placeholders'])) {
+        return FALSE;
+      }
+      $data[$placeholder] = $cached_element;
+    }
+    static::$cachePlaceholders = array_merge(static::$cachePlaceholders, $data);
+
+    return TRUE;
+  }
+
   /**
    * Caches the rendered output of a renderable element.
    *
@@ -530,7 +591,19 @@ protected function cacheSet(array &$elements) {
 
 
     $bin = isset($elements['#cache']['bin']) ? $elements['#cache']['bin'] : 'render';
     $expire = isset($elements['#cache']['expire']) ? $elements['#cache']['expire'] : Cache::PERMANENT;
-    $this->cacheFactory->get($bin)->set($cid, $data, $expire, $data['#cache']['tags']);
+    $cache = $this->cacheFactory->get($bin);
+
+    // This assumes bubbling worked correctly and createCacheID() working on contexts instead of cache keys.
+    if (isset($elements['#cache_old_id']) && $cid != $elements['#cache_old_id']) {
+      $cache_old_id = $elements['#cache_old_id'];
+      $placeholder = '<!-- PLACEHOLDER: ' . $cache_old_id . ' -->';
+      
+      $elements = [ '#markup' => $placeholder ];
+      $elements['#cache']['placeholders'][$placeholder] = [ '#cache' => $elements['#cache'] ];
+      $this->cacheFactory->get('render')->set($cache_old_id, $elements, $expire, $data['#cache']['tags']);
+      static::$cachePlaceholders[$placeholder] = $data;
+    }
+    $cache->set($cid, $data, $expire, $data['#cache']['tags']);
   }
 
   /**
@@ -569,6 +642,7 @@ public function getCacheableRenderArray(array $elements) {
       '#post_render_cache' => $elements['#post_render_cache'],
       '#cache' => [
         'tags' => $elements['#cache']['tags'],
+        'placeholders' => $elements['#cache']['placeholders'],
       ],
     ];
   }