Trace me

gistfile1.diff

diff --git a/core/lib/Drupal/Core/Form/FormCache.php b/core/lib/Drupal/Core/Form/FormCache.php
index a35000d..6ddcccc 100644
--- a/core/lib/Drupal/Core/Form/FormCache.php
+++ b/core/lib/Drupal/Core/Form/FormCache.php
@@ -212,8 +212,40 @@ public function setCache($form_build_id, $form, FormStateInterface $form_state)
     $form_state->addBuildInfo('safe_strings', SafeMarkup::getAll());
 
     if ($data = $form_state->getCacheableArray()) {
+      $this->traceMe($data);
       $this->keyValueExpirableFactory->get('form_state')->setWithExpire($form_build_id, $data, $expire);
     }
   }
 
+  protected function traceMe(array $array, $depth = 0) {
+    if ($depth == 10) {
+      print str_repeat('- ', $depth) . "RECURSION\n";
+      return;
+    }
+    foreach ($array as $key => $value) {
+      if (is_array($value)) {
+        print str_repeat('- ', $depth) . "$key:\n";
+        $this->traceMe($value, $depth + 1);
+      }
+      elseif (is_object($value)) {
+        print str_repeat('- ', $depth) . "$key: " . get_class($value) . "\n";
+        if (method_exists($value, '__sleep')) {
+          $properties = $value->__sleep();
+          $reflection_object = new \ReflectionObject($value);
+          $value_array = [];
+
+          foreach ($properties as $property) {
+            $reflection_property = $reflection_object->getProperty($property);
+            $reflection_property->setAccessible(TRUE);
+            $value_array[$property] = $reflection_property->getValue($value);
+          }
+        }
+        else {
+          $value_array = (array) $value;
+        }
+        $this->traceMe($value_array, $depth + 1);
+      }
+    }
+  }
+
 }