PR fixes.

_config/versionedownership.yml

@@ -12,3 +12,9 @@ OnlyIf:
 SilverStripe\Admin\LeftAndMain:
   extensions:
     RecursivePublishableHandler: SilverStripe\Versioned\RecursivePublishableHandler
+---
+Name: versionedrecursivestages
+---
+SilverStripe\Core\Injector\Injector:
+  SilverStripe\Versioned\RecursiveStagesInterface:
+    class: SilverStripe\Versioned\RecursiveStagesService

src/RecursiveStagesInterface.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace SilverStripe\Versioned;
+
+use SilverStripe\ORM\DataObject;
+
+/**
+ * Interface RecursiveStagesInterface
+ *
+ * Interface for @see RecursiveStagesService to provide the capability to for "smart" durty model state
+ * which can cover nested models
+ */
+interface RecursiveStagesInterface
+{
+
+    /**
+     * Determine if content differs on stages including nested objects
+     *
+     * @param DataObject $object
+     * @param string $mode
+     * @return bool
+     */
+    public function stagesDifferRecursive(DataObject $object, string $mode): bool;
+}

src/RecursiveStagesService.php

@@ -3,18 +3,15 @@
 namespace SilverStripe\Versioned;
 
 use SilverStripe\Core\Injector\Injectable;
-use SilverStripe\ORM\DataList;
 use SilverStripe\ORM\DataObject;
 use SilverStripe\ORM\SS_List;
 
 /**
  * Class RecursiveStagesService
  *
  * Functionality for detecting the need of publishing nested objects owned by common parent / ancestor object
- *
- * @package SilverStripe\Versioned
  */
-class RecursiveStagesService
+class RecursiveStagesService implements RecursiveStagesInterface
 {
     use Injectable;
 

src/Versioned.php

@@ -11,6 +11,7 @@
 use SilverStripe\Core\ClassInfo;
 use SilverStripe\Core\Config\Config;
 use SilverStripe\Core\Extension;
+use SilverStripe\Core\Injector\Injector;
 use SilverStripe\Core\Resettable;
 use SilverStripe\Dev\Deprecation;
 use SilverStripe\Forms\FieldList;
@@ -2071,7 +2072,10 @@ public function stagesDiffer()
      */
     public function stagesDifferRecursive(string $mode = RecursiveStagesService::OWNERSHIP_STRONG): bool
     {
-        return RecursiveStagesService::singleton()->stagesDifferRecursive($this->owner, $mode);
+        /** @var RecursiveStagesInterface $service */
+        $service = Injector::inst()->get(RecursiveStagesInterface::class);
+
+        return $service->stagesDifferRecursive($this->owner, $mode);
     }
 
     /**