Issue #2994550 by tedbow, tim.plunkett, gapple, johndevman, Wim Leers, neclimdul, EclipseGc, catch: Filtering block plugins by context is slow

(cherry picked from commit 2753c01)

Author: xjm

lib/Drupal/Core/Plugin/Context/ContextHandler.php

@@ -17,12 +17,19 @@ class ContextHandler implements ContextHandlerInterface {
    * {@inheritdoc}
    */
   public function filterPluginDefinitionsByContexts(array $contexts, array $definitions) {
-    return array_filter($definitions, function ($plugin_definition) use ($contexts) {
+    $checked_requirements = [];
+    return array_filter($definitions, function ($plugin_definition) use ($contexts, &$checked_requirements) {
       $context_definitions = $this->getContextDefinitions($plugin_definition);
-
       if ($context_definitions) {
-        // Check the set of contexts against the requirements.
-        return $this->checkRequirements($contexts, $context_definitions);
+        // Generate a unique key for the current context definitions. This will
+        // allow calling checkRequirements() once for all plugins that have the
+        // same context definitions.
+        $context_definitions_key = hash('sha256', serialize($context_definitions));
+        if (!isset($checked_requirements[$context_definitions_key])) {
+          // Check the set of contexts against the requirements.
+          $checked_requirements[$context_definitions_key] = $this->checkRequirements($contexts, $context_definitions);
+        }
+        return $checked_requirements[$context_definitions_key];
       }
       // If this plugin doesn't need any context, it is available to use.
       return TRUE;