MAGETWO-87564: [2.3] Add fallback for product links position attribute #13437

 - Merge Pull Request #13437 from ihor-sviziev/magento2:Add-fallback-for-Product_links-position-attribute
 - Merged commits:
   1. e765098
   2. d83c90a

Author: mzeis

app/code/Magento/Catalog/Model/Product/Link/SaveHandler.php

@@ -31,6 +31,7 @@ class SaveHandler
     private $linkResource;
 
     /**
+     * SaveHandler constructor.
      * @param MetadataPool $metadataPool
      * @param Link $linkResource
      * @param ProductLinkRepositoryInterface $productLinkRepository
@@ -55,17 +56,50 @@ public function execute($entityType, $entity)
     {
         $link = $entity->getData($this->metadataPool->getMetadata($entityType)->getLinkField());
         if ($this->linkResource->hasProductLinks($link)) {
-            /** @var \Magento\Catalog\Api\Data\ProductInterface $entity*/
+            /** @var \Magento\Catalog\Api\Data\ProductInterface $entity */
             foreach ($this->productLinkRepository->getList($entity) as $link) {
                 $this->productLinkRepository->delete($link);
             }
         }
-        $productLinks = $entity->getProductLinks();
+
+        // Build links per type
+        $linksByType = [];
+        foreach ($entity->getProductLinks() as $link) {
+            $linksByType[$link->getLinkType()][] = $link;
+        }
+
+        // Set array position as a fallback position if necessary
+        foreach ($linksByType as $linkType => $links) {
+            if (!$this->hasPosition($links)) {
+                array_walk($linksByType[$linkType], function ($productLink, $position) {
+                    $productLink->setPosition(++$position);
+                });
+            }
+        }
+
+        // Flatten multi-dimensional linksByType in ProductLinks
+        $productLinks = array_reduce($linksByType, 'array_merge', []);
+
         if (count($productLinks) > 0) {
             foreach ($entity->getProductLinks() as $link) {
                 $this->productLinkRepository->save($link);
             }
         }
         return $entity;
     }
+
+    /**
+     * Check if at least one link without position
+     * @param array $links
+     * @return bool
+     */
+    private function hasPosition(array $links)
+    {
+        foreach ($links as $link) {
+            if (!array_key_exists('position', $link->getData())) {
+                return false;
+            }
+        }
+        return true;
+    }
 }