fix: do not cast BackedEnum identifiers

src/Proxy/ProxyGenerator.php

@@ -940,12 +940,16 @@ private function generateMethods(ClassMetadata $class)
             if ($this->isShortIdentifierGetter($method, $class)) {
                 $identifier = lcfirst(substr($name, 3));
                 $fieldType  = $class->getTypeOfField($identifier);
-                $cast       = in_array($fieldType, ['integer', 'smallint'], true) ? '(int) ' : '';
+                $castToInt  = in_array($fieldType, ['integer', 'smallint'], true);
 
                 $methods .= '        if ($this->__isInitialized__ === false) {' . "\n";
                 $methods .= '            ';
                 $methods .= $this->shouldProxiedMethodReturn($method) ? 'return ' : '';
-                $methods .= $cast . ' parent::' . $method->getName() . "();\n";
+                if ($castToInt) {
+                    $methods .= '! parent::' . $method->getName() . '() instanceof \BackedEnum ';
+                    $methods .= '? (int) parent::' . $method->getName() . '() : ';
+                }
+                $methods .= 'parent::' . $method->getName() . "();\n";
                 $methods .= '        }' . "\n\n";
             }
 

tests/Common/Proxy/LazyLoadableObjectWithPHP81EnumIntType.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Doctrine\Tests\Common\Proxy;
+
+class LazyLoadableObjectWithPHP81EnumIntType
+{
+    private LazyLoadableObjectWithPHP81EnumIntTypeIdentfier $identifierFieldEnumIntType;
+
+    public function getIdentifierFieldEnumIntType(): LazyLoadableObjectWithPHP81EnumIntTypeIdentfier
+    {
+        return $this->identifierFieldEnumIntType;
+    }
+
+    public static function getFooIdentifier(): LazyLoadableObjectWithPHP81EnumIntTypeIdentfier
+    {
+        return LazyLoadableObjectWithPHP81EnumIntTypeIdentfier::FOO;
+    }
+}
+
+enum LazyLoadableObjectWithPHP81EnumIntTypeIdentfier: int
+{
+    case FOO = 1;
+    case BAR = 2;
+}

tests/Common/Proxy/LazyLoadableObjectWithPHP81EnumIntTypeClassMetadata.php

@@ -0,0 +1,157 @@
+<?php
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Common\Proxy;
+
+use BadMethodCallException;
+use Doctrine\Persistence\Mapping\ClassMetadata;
+use ReflectionClass;
+use function array_keys;
+
+class LazyLoadableObjectWithPHP81EnumIntTypeClassMetadata implements ClassMetadata
+{
+    /** @var ReflectionClass */
+    protected $reflectionClass;
+
+    /** @var array<string,bool> */
+    protected $identifier = [
+        'identifierFieldEnumIntType' => true,
+    ];
+
+    /** @var array<string,bool> */
+    protected $fields = [
+        'identifierFieldEnumIntType' => true,
+    ];
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getName()
+    {
+        return $this->getReflectionClass()->getName();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getIdentifier()
+    {
+        return array_keys($this->identifier);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getReflectionClass()
+    {
+        if ($this->reflectionClass === null) {
+            $this->reflectionClass = new ReflectionClass(__NAMESPACE__ . '\LazyLoadableObjectWithPHP81EnumIntType');
+        }
+
+        return $this->reflectionClass;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function isIdentifier($fieldName)
+    {
+        return isset($this->identifier[$fieldName]);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function hasField($fieldName)
+    {
+        return isset($this->fields[$fieldName]);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function hasAssociation($fieldName)
+    {
+        return false;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function isSingleValuedAssociation($fieldName)
+    {
+        throw new BadMethodCallException('not implemented');
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function isCollectionValuedAssociation($fieldName)
+    {
+        throw new BadMethodCallException('not implemented');
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getFieldNames()
+    {
+        return array_keys($this->fields);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getIdentifierFieldNames()
+    {
+        return $this->getIdentifier();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getAssociationNames()
+    {
+        return [];
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getTypeOfField($fieldName)
+    {
+        return 'integer';
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getAssociationTargetClass($assocName)
+    {
+        throw new BadMethodCallException('not implemented');
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function isAssociationInverseSide($assocName)
+    {
+        throw new BadMethodCallException('not implemented');
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getAssociationMappedByTargetField($assocName)
+    {
+        throw new BadMethodCallException('not implemented');
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getIdentifierValues($object)
+    {
+        throw new BadMethodCallException('not implemented');
+    }
+}

tests/Common/Proxy/ProxyLogicIdentifierGetterTest.php

@@ -75,6 +75,7 @@ public function methodsForWhichLazyLoadingShouldBeDisabled()
         ];
 
         if (PHP_VERSION_ID >= 80000) {
+            $data[] = [new LazyLoadableObjectWithPHP81EnumIntTypeClassMetadata(), 'identifierFieldEnumIntType', LazyLoadableObjectWithPHP81EnumIntType::getFooIdentifier()];
             $data[] = [new LazyLoadableObjectWithPHP8UnionTypeClassMetadata(), 'identifierFieldUnionType', 123];
             $data[] = [new LazyLoadableObjectWithPHP8UnionTypeClassMetadata(), 'identifierFieldUnionType', 'string'];
         }