Add regression test for #8108

tests/Tests/ORM/Functional/Ticket/Issue8108Test.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\ORM\Mapping\Column;
+use Doctrine\ORM\Mapping\DiscriminatorMap;
+use Doctrine\ORM\Mapping\Entity;
+use Doctrine\ORM\Mapping\Id;
+use Doctrine\ORM\Mapping\InheritanceType;
+use Doctrine\ORM\Mapping\ManyToOne;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+class Issue8108Test extends OrmFunctionalTestCase
+{
+    public function testIssue(): void
+    {
+        $this->createSchemaForModels(
+            Issue8108User::class,
+            Issue8108Base::class,
+            Issue8108Extending::class,
+        );
+    }
+}
+
+#[Entity]
+class Issue8108User
+{
+    public function __construct(
+        #[Id]
+        #[Column]
+        public int $id,
+    ) {
+    }
+}
+
+abstract class Issue8108WithRelation
+{
+    #[ManyToOne(targetEntity: Issue8108User::class)]
+    public Issue8108User|null $createdBy;
+}
+
+#[Entity]
+#[InheritanceType('SINGLE_TABLE')]
+#[DiscriminatorMap(['extending' => Issue8108Extending::class])]
+abstract class Issue8108Base extends Issue8108WithRelation
+{
+    #[Id]
+    #[Column]
+    public int $id;
+}
+
+#[Entity]
+class Issue8108Extending extends Issue8108Base
+{
+}