From 95ed67ee4adbbd7f3f0107a52da4b9238cf44803 Mon Sep 17 00:00:00 2001
From: Magento EngCom Team <magento-engcom-team@magento.com>
Date: Tue, 23 Jan 2018 11:00:33 -0600
Subject: [PATCH] :arrow_double_up: Forwardport of magento/magento2#12001 to
 2.3-develop branch

Applied pull request patch https://github.com/magento/magento2/pull/12001.patch (created by @RomaKis) based on commit(s):
  1. 17aa13c9664fd55d02e535131b0d882102e61aab
  2. 3f79b80549bf42ebf96ead47d39824d949723daa

Fixed GitHub Issues in 2.3-develop branch:
  - magento/magento2#11532: Duplicate Simple Product Throws Error: Undefined offset: 0 in SaveHandler.php on line 122 (reported by @lee586)
---
 .../Catalog/Model/Category/Link/SaveHandler.php   |  4 +++-
 .../Unit/Model/Category/Link/SaveHandlerTest.php  | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php b/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php
index 29a1ef60a43de..f22c6903a230c 100644
--- a/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php
+++ b/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php
@@ -119,7 +119,9 @@ private function mergeCategoryLinks($newCategoryPositions, $oldCategoryPositions
 
             if ($key === false) {
                 $result[] = $newCategoryPosition;
-            } elseif ($oldCategoryPositions[$key]['position'] != $newCategoryPosition['position']) {
+            } elseif (isset($oldCategoryPositions[$key])
+                && $oldCategoryPositions[$key]['position'] != $newCategoryPosition['position']
+            ) {
                 $result[] = $newCategoryPositions[$key];
                 unset($oldCategoryPositions[$key]);
             }
diff --git a/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php b/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php
index 78db12be56b42..0b85ef38387fa 100644
--- a/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php
+++ b/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php
@@ -197,6 +197,21 @@ public function getCategoryDataProvider()
                 ],
                 [], //affected category_ids
             ],
+            [
+                [3], //model category_ids
+                [
+                    ['category_id' => 3, 'position' => 20],
+                    ['category_id' => 4, 'position' => 30],
+                ], // dto category links
+                [
+                    ['category_id' => 3, 'position' => 10],
+                ],
+                [
+                    ['category_id' => 3, 'position' => 20],
+                    ['category_id' => 4, 'position' => 30],
+                ],
+                [3, 4], //affected category_ids
+            ],
         ];
     }