[TypeDeclaration] Allow interface return change to exact return on private method on NarrowObjectReturnTypeRector

rules-tests/TypeDeclaration/Rector/ClassMethod/NarrowObjectReturnTypeRector/Fixture/allow_interface_return_on_private_method.php.inc

@@ -0,0 +1,33 @@
+<?php
+
+namespace Rector\Tests\TypeDeclaration\Rector\ClassMethod\NarrowObjectReturnTypeRector\Fixture;
+
+use Rector\Tests\TypeDeclaration\Rector\ClassMethod\NarrowObjectReturnTypeRector\Source\TalkInterface;
+use Rector\Tests\TypeDeclaration\Rector\ClassMethod\NarrowObjectReturnTypeRector\Source\ConferenceTalkImplementation;
+
+final class AllowInterfaceReturnOnPrivateMethod
+{
+    private function create(): TalkInterface
+    {
+        return new ConferenceTalkImplementation();
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\TypeDeclaration\Rector\ClassMethod\NarrowObjectReturnTypeRector\Fixture;
+
+use Rector\Tests\TypeDeclaration\Rector\ClassMethod\NarrowObjectReturnTypeRector\Source\TalkInterface;
+use Rector\Tests\TypeDeclaration\Rector\ClassMethod\NarrowObjectReturnTypeRector\Source\ConferenceTalkImplementation;
+
+final class AllowInterfaceReturnOnPrivateMethod
+{
+    private function create(): \Rector\Tests\TypeDeclaration\Rector\ClassMethod\NarrowObjectReturnTypeRector\Source\ConferenceTalkImplementation
+    {
+        return new ConferenceTalkImplementation();
+    }
+}
+
+?>

rules/TypeDeclaration/Rector/ClassMethod/NarrowObjectReturnTypeRector.php

@@ -150,7 +150,8 @@ public function refactor(Node $node): ?Node
             }
 
             // this rule narrows only object or class types, not interfaces
-            if (! $declaredTypeClassReflection->isClass()) {
+            // except private methods, as they are not part of contract, and not mockable from tests
+            if (! $declaredTypeClassReflection->isClass() && ! $node->isPrivate()) {
                 return null;
             }
         }