ENGCOM-5631: Extract handles from layout updates before layout merge step. #23918

Author: sidolov

lib/internal/Magento/Framework/View/Model/Layout/Merge.php

@@ -18,6 +18,7 @@
  * Layout merge model
  * @SuppressWarnings(PHPMD.TooManyFields)
  * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
+ * @SuppressWarnings(PHPMD.ExcessiveClassComplexity)
  */
 class Merge implements \Magento\Framework\View\Layout\ProcessorInterface
 {
@@ -462,6 +463,8 @@ public function load($handles = [])
             return $this;
         }
 
+        $this->extractHandlers();
+
         foreach ($this->getHandles() as $handle) {
             $this->_merge($handle);
         }
@@ -951,4 +954,25 @@ public function getCacheId()
         // phpcs:ignore Magento2.Security.InsecureFunction
         return $this->generateCacheId(md5(implode('|', array_merge($this->getHandles(), $layoutCacheKeys))));
     }
+
+    /**
+     * Walk all updates and extract handles before the merge step.
+     */
+    private function extractHandlers(): void
+    {
+        foreach ($this->updates as $update) {
+            $updateXml = null;
+
+            try {
+                $updateXml = $this->_loadXmlString($update);
+                // phpcs:ignore Magento2.CodeAnalysis.EmptyBlock
+            } catch (\Exception $exception) {
+                // ignore invalid
+            }
+
+            if ($updateXml && strtolower($updateXml->getName()) == 'update' && isset($updateXml['handle'])) {
+                $this->addHandle((string)$updateXml['handle']);
+            }
+        }
+    }
 }