Failing test: Duplicate private fields not detected

This test case demonstrates a situation where two entities inherit from each other. Both entity classes have a private property named `field`. (Inheritance is set up correctly, but that is irrelevant here.)

Technically, that's two properties on two separate classes. Also, the mapping configuration given suggests to put both properties into separate database columns.

I think this violates fundamental design assumptions, since `ClassMetadata::$fieldMappings` is indexed by "field name" – there is no room for juggling with duplicate private fields being declared in different classes. My guess is this is a design limitation that would be very hard to change, should be documented as a limitation and be rejected when it is noticed.

The same applies to association mappings and embeddables.

The current situation, however, is that the property and mapping configuration will be picked up from the first (parent) entity class.

At least the annotation and attribute mapping driver will then silently skip the property on the subclass (see doctrine#10417).

Mapping configuration for `GH10450ChildClass::$field` will never be considered. This property will (silently) remain unmapped.

Author: mpdude

tests/Doctrine/Tests/ORM/Functional/Ticket/GH10450Test.php

@@ -0,0 +1,106 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\ORM\Mapping\MappingException;
+use Doctrine\Tests\OrmTestCase;
+use Generator;
+
+class GH10450Test extends OrmTestCase
+{
+    /**
+     * @param class-string $className
+     *
+     * @dataProvider classesThatOverrideFieldNames
+     */
+    public function testDuplicatePrivateFieldsShallBeRejected(string $className): void
+    {
+        $em = $this->getTestEntityManager();
+
+        $this->expectException(MappingException::class);
+
+        $em->getClassMetadata($className);
+    }
+
+    public function classesThatOverrideFieldNames(): Generator
+    {
+        yield 'Entity class that redeclares a private field inherited from a base entity' => [GH10450EntityChild::class];
+        yield 'Entity class that redeclares a private field inherited from a mapped superclass' => [GH10450MappedSuperclassChild::class];
+    }
+}
+
+/**
+ * @ORM\Entity
+ * @ORM\InheritanceType("JOINED")
+ * @ORM\DiscriminatorMap({ "base": "GH10450BaseEntity", "child": "GH10450EntityChild" })
+ * @ORM\DiscriminatorColumn(name="type")
+ */
+class GH10450BaseEntity
+{
+    /**
+     * @ORM\Column(type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    private $id;
+
+    /**
+     * @ORM\Column(type="text", name="base")
+     *
+     * @var string
+     */
+    private $field;
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH10450EntityChild extends GH10450BaseEntity
+{
+    /**
+     * @ORM\Column(type="text", name="child")
+     *
+     * @var string
+     */
+    private $field;
+}
+
+/**
+ * @ORM\MappedSuperclass
+ */
+class GH10450BaseMappedSuperclass
+{
+    /**
+     * @ORM\Column(type="integer")
+     * @ORM\Id
+     * @ORM\GeneratedValue
+     *
+     * @var int
+     */
+    private $id;
+
+    /**
+     * @ORM\Column(type="text", name="base")
+     *
+     * @var string
+     */
+    private $field;
+}
+
+/**
+ * @ORM\Entity
+ */
+class GH10450MappedSuperclassChild extends GH10450BaseMappedSuperclass
+{
+    /**
+     * @ORM\Column(type="text", name="child")
+     *
+     * @var string
+     */
+    private $field;
+}