MAGETWO-62271: Inconsistent saving of Stock Data

Author: Valeriy Nayda

app/code/Magento/Catalog/Model/Product/Copier.php

@@ -60,7 +60,12 @@ public function copy(\Magento\Catalog\Model\Product $product)
         /** @var \Magento\Catalog\Model\Product $duplicate */
         $duplicate = $this->productFactory->create();
         $productData = $product->getData();
-        unset($productData[ProductInterface::EXTENSION_ATTRIBUTES_KEY]);
+        if (isset($productData[ProductInterface::EXTENSION_ATTRIBUTES_KEY])) {
+            $extensionAttributes = $productData[ProductInterface::EXTENSION_ATTRIBUTES_KEY];
+            if (null !== $extensionAttributes->getStockItem()) {
+                $extensionAttributes->setData('stock_item', null);
+            }
+        }
         $duplicate->setData($productData);
         $duplicate->setOptions([]);
         $duplicate->setIsDuplicate(true);

app/code/Magento/Catalog/Test/Unit/Model/Product/CopierTest.php

@@ -81,9 +81,23 @@ protected function setUp()
 
     public function testCopy()
     {
+        $stockItem = $this->getMockBuilder(\Magento\CatalogInventory\Api\Data\StockItemInterface::class)
+            ->getMock();
+        $extensionAttributes = $this->getMockBuilder(\Magento\Catalog\Api\Data\ProductExtension::class)
+            ->setMethods(['getStockItem', 'setData'])
+            ->getMock();
+        $extensionAttributes
+            ->expects($this->once())
+            ->method('getStockItem')
+            ->willReturn($stockItem);
+        $extensionAttributes
+            ->expects($this->once())
+            ->method('setData')
+            ->with('stock_item', null);
+
         $productData = [
             'product data' => ['product data'],
-            ProductInterface::EXTENSION_ATTRIBUTES_KEY => [],
+            ProductInterface::EXTENSION_ATTRIBUTES_KEY => $extensionAttributes,
         ];
         $this->productMock->expects($this->atLeastOnce())->method('getWebsiteIds');
         $this->productMock->expects($this->atLeastOnce())->method('getCategoryIds');
@@ -140,7 +154,7 @@ public function testCopy()
         )->with(
             \Magento\Store\Model\Store::DEFAULT_STORE_ID
         );
-        $duplicateMock->expects($this->once())->method('setData')->with(['product data' => ['product data']]);
+        $duplicateMock->expects($this->once())->method('setData')->with($productData);
         $this->copyConstructorMock->expects($this->once())->method('build')->with($this->productMock, $duplicateMock);
         $duplicateMock->expects($this->once())->method('getUrlKey')->willReturn('urk-key-1');
         $duplicateMock->expects($this->once())->method('setUrlKey')->with('urk-key-2');