Fixed indexed product positions for anchor categories.

Author: Evgeni Obukhovsky

app/code/Magento/Catalog/Model/Indexer/Category/Product/AbstractAction.php

@@ -431,6 +431,10 @@ protected function createAnchorSelect(\Magento\Store\Model\Store $store)
             ['ccp' => $this->getTable('catalog_category_product')],
             'ccp.category_id = cc2.child_id',
             []
+        )->joinLeft(
+            ['ccp2' => $this->getTable('catalog_category_product')],
+            'ccp2.category_id = cc2.parent_id AND ccp.product_id = ccp2.product_id',
+            []
         )->joinInner(
             ['cpe' => $this->getTable('catalog_product_entity')],
             'ccp.product_id = cpe.entity_id',
@@ -493,7 +497,7 @@ protected function createAnchorSelect(\Magento\Store\Model\Store $store)
             [
                 'category_id' => 'cc.entity_id',
                 'product_id' => 'ccp.product_id',
-                'position' => new \Zend_Db_Expr('ccp.position + 10000'),
+                'position' => new \Zend_Db_Expr($this->connection->getIfNullSql('ccp2.position', 'ccp.position + 10000')),
                 'is_parent' => new \Zend_Db_Expr('0'),
                 'store_id' => new \Zend_Db_Expr($store->getId()),
                 'visibility' => new \Zend_Db_Expr($this->connection->getIfNullSql('cpvs.value', 'cpvd.value')),