Fixing the error "Not all of your products are available in the requested quantity." when admin try create a shipment with backorder items

github-issue-21646.patch

From 55dbc56b22f609c1b1a943f71566569f6f7affb0 Mon Sep 17 00:00:00 2001
From: Denis Colli Spalenza <[email protected]>
Date: Thu, 8 Oct 2020 21:01:08 -0300
Subject: [PATCH] Adding support to backorders

---
 Model/SourceDeductionService.php | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Model/SourceDeductionService.php b/Model/SourceDeductionService.php
index 142e569..9458f00 100644
--- a/Model/SourceDeductionService.php
+++ b/Model/SourceDeductionService.php
@@ -73,8 +73,11 @@ class SourceDeductionService implements SourceDeductionServiceInterface
                 $stockId
             );
 
-            if (!$stockItemConfiguration->isManageStock()) {
-                //We don't need to Manage Stock
+            $isBackorders = $stockItemConfiguration->getBackorders() == \Magento\CatalogInventory\Model\Stock::BACKORDERS_YES_NONOTIFY
+                || $stockItemConfiguration->getBackorders() == \Magento\CatalogInventory\Model\Stock::BACKORDERS_YES_NOTIFY;
+
+            if (!$stockItemConfiguration->isManageStock() || $isBackorders) {
+                //We don't need to Manage Stock or backorder products
                 continue;
             }
 
-- 
2.21.1 (Apple Git-122.3)