Throw exception when trying to use non-backed enum types

lib/Doctrine/ORM/Mapping/DefaultTypedFieldMapper.php

@@ -57,7 +57,15 @@ public function validateAndComplete(array $mapping, ReflectionProperty $field):
                 $mapping['enumType'] = $type->getName();
 
                 $reflection = new ReflectionEnum($type->getName());
-                $type       = $reflection->getBackingType();
+                if (! $reflection->isBacked()) {
+                    throw MappingException::backedEnumTypeRequired(
+                        $field->class,
+                        $mapping['fieldName'],
+                        $mapping['enumType']
+                    );
+                }
+
+                $type = $reflection->getBackingType();
 
                 assert($type instanceof ReflectionNamedType);
             }

lib/Doctrine/ORM/Mapping/MappingException.php

@@ -954,6 +954,16 @@ public static function enumsRequirePhp81(string $className, string $fieldName):
         return new self(sprintf('Enum types require PHP 8.1 in %s::$%s', $className, $fieldName));
     }
 
+    public static function backedEnumTypeRequired(string $className, string $fieldName, string $enumType): self
+    {
+        return new self(sprintf(
+            'Attempting to map a non-backed enum type %s in entity %s::$%s. Please use backed enums only',
+            $enumType,
+            $className,
+            $fieldName
+        ));
+    }
+
     public static function nonEnumTypeMapped(string $className, string $fieldName, string $enumType): self
     {
         return new self(sprintf(

tests/Doctrine/Tests/Models/Enums/FaultySwitch.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Models\Enums;
+
+use Doctrine\ORM\Mapping\Column;
+
+class FaultySwitch
+{
+    #[Column(type: 'string')]
+    public string $value;
+
+    /**
+     * The following line is ignored on psalm and phpstan so that we can test
+     * that the mapping is throwing an exception when a non-backed enum is used.
+     *
+     * @psalm-suppress InvalidArgument
+     */
+    #[Column(enumType: SwitchStatus::class)]
+    public SwitchStatus $status;
+}

tests/Doctrine/Tests/Models/Enums/SwitchStatus.php

@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Models\Enums;
+
+enum SwitchStatus
+{
+    case ON;
+    case OFF;
+}

tests/Doctrine/Tests/ORM/Mapping/TypedEnumFieldMapperTest.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\ORM\Mapping;
+
+use Doctrine\ORM\Mapping\DefaultTypedFieldMapper;
+use Doctrine\ORM\Mapping\MappingException;
+use Doctrine\Tests\Models\Enums\FaultySwitch;
+use Doctrine\Tests\OrmTestCase;
+use ReflectionClass;
+
+/**
+ * @requires PHP >= 8.1
+ */
+class TypedEnumFieldMapperTest extends OrmTestCase
+{
+    private static function defaultTypedFieldMapper(): DefaultTypedFieldMapper
+    {
+        return new DefaultTypedFieldMapper();
+    }
+
+    public function testNotBackedEnumThrows(): void
+    {
+        $reflectionClass = new ReflectionClass(FaultySwitch::class);
+
+        $this->expectException(MappingException::class);
+        $this->expectExceptionMessage(
+            'Attempting to map a non-backed enum type Doctrine\Tests\Models\Enums\SwitchStatus in entity Doctrine\Tests\Models\Enums\FaultySwitch::$status. Please use backed enums only'
+        );
+
+        self::defaultTypedFieldMapper()->validateAndComplete(['fieldName' => 'status'], $reflectionClass->getProperty('status'));
+    }
+}