MAGETWO-87358: #12717 - Catalog Products List widget is not displayed on Storefront #12765

 - Merge Pull Request #12765 from RostislavS/magento2:issue12717
 - Merged commits:
   1. d30696e
   2. 55a3ded

Author: dmanners

app/code/Magento/Catalog/Model/ResourceModel/Eav/Attribute.php

@@ -230,6 +230,16 @@ public function afterSave()
         return parent::afterSave();
     }
 
+    /**
+     * Is attribute enabled for flat indexing
+     *
+     * @return bool
+     */
+    public function isEnabledInFlat()
+    {
+        return $this->_isEnabledInFlat();
+    }
+
     /**
      * Is attribute enabled for flat indexing
      *

app/code/Magento/CatalogWidget/Model/Rule/Condition/Product.php

@@ -119,8 +119,21 @@ public function addToCollection($collection)
         $attribute = $this->getAttributeObject();
 
         if ($collection->isEnabledFlat()) {
-            $alias = array_keys($collection->getSelect()->getPart('from'))[0];
-            $this->joinedAttributes[$attribute->getAttributeCode()] = $alias . '.' . $attribute->getAttributeCode();
+            if ($attribute->isEnabledInFlat()) {
+                $alias = array_keys($collection->getSelect()->getPart('from'))[0];
+                $this->joinedAttributes[$attribute->getAttributeCode()] = $alias . '.' . $attribute->getAttributeCode();
+            } else {
+                $alias = 'at_' . $attribute->getAttributeCode();
+                if (!in_array($alias, array_keys($collection->getSelect()->getPart('from')))) {
+                    $collection->joinAttribute(
+                        $attribute->getAttributeCode(),
+                        'catalog_product/'.$attribute->getAttributeCode(),
+                        'entity_id'
+                    );
+                }
+
+                $this->joinedAttributes[$attribute->getAttributeCode()] = $alias . '.value';
+            }
             return $this;
         }