Deprecate reliance on sequence-emulated identity columns

UPGRADE.md

@@ -1,5 +1,10 @@
 # Upgrade to 2.13
 
+## Deprecated using the `IDENTITY` identifier strategy on platform that do not support identity columns
+
+If identity columns are emulated with sequences on the platform you are using,
+you should switch to the `SEQUENCE` strategy.
+
 ## Deprecated passing `null` to `Doctrine\ORM\Query::setFirstResult()`
 
 `$query->setFirstResult(null);` is equivalent to `$query->setFirstResult(0)`.

lib/Doctrine/ORM/Id/BigIntegerIdentityGenerator.php

@@ -4,6 +4,7 @@
 
 namespace Doctrine\ORM\Id;
 
+use Doctrine\Deprecations\Deprecation;
 use Doctrine\ORM\EntityManagerInterface;
 
 /**
@@ -27,6 +28,15 @@ class BigIntegerIdentityGenerator extends AbstractIdGenerator
      */
     public function __construct($sequenceName = null)
     {
+        if ($sequenceName !== null) {
+            Deprecation::trigger(
+                'doctrine/orm',
+                'https://github.com/doctrine/orm/issues/8850',
+                'Passing a sequence name to the IdentityGenerator is deprecated in favor of using %s. $sequenceName will be removed in ORM 3.0',
+                SequenceGenerator::class
+            );
+        }
+
         $this->sequenceName = $sequenceName;
     }
 

lib/Doctrine/ORM/Id/IdentityGenerator.php

@@ -4,6 +4,7 @@
 
 namespace Doctrine\ORM\Id;
 
+use Doctrine\Deprecations\Deprecation;
 use Doctrine\ORM\EntityManagerInterface;
 
 /**
@@ -27,6 +28,15 @@ class IdentityGenerator extends AbstractIdGenerator
      */
     public function __construct($sequenceName = null)
     {
+        if ($sequenceName !== null) {
+            Deprecation::trigger(
+                'doctrine/orm',
+                'https://github.com/doctrine/orm/issues/8850',
+                'Passing a sequence name to the IdentityGenerator is deprecated in favor of using %s. $sequenceName will be removed in ORM 3.0',
+                SequenceGenerator::class
+            );
+        }
+
         $this->sequenceName = $sequenceName;
     }
 

lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php

@@ -33,6 +33,7 @@
 use function count;
 use function end;
 use function explode;
+use function get_class;
 use function in_array;
 use function is_subclass_of;
 use function str_contains;
@@ -558,6 +559,18 @@ private function completeIdGeneratorMapping(ClassMetadataInfo $class): void
 
                 // Platforms that do not have native IDENTITY support need a sequence to emulate this behaviour.
                 if ($this->getTargetPlatform()->usesSequenceEmulatedIdentityColumns()) {
+                    Deprecation::trigger(
+                        'doctrine/orm',
+                        'https://github.com/doctrine/orm/issues/8850',
+                        <<<'DEPRECATION'
+Context: Loading metadata for class %s
+Problem: Using the IDENTITY generator strategy with platform "%s" is deprecated and will not be possible in Doctrine ORM 3.0.
+Solution: Use the SEQUENCE generator strategy instead.
+DEPRECATION
+                            ,
+                        $class->name,
+                        get_class($this->getTargetPlatform())
+                    );
                     $columnName     = $class->getSingleIdentifierColumnName();
                     $quoted         = isset($class->fieldMappings[$fieldName]['quoted']) || isset($class->table['quoted']);
                     $sequencePrefix = $class->getSequencePrefix($this->getTargetPlatform());

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

@@ -97,6 +97,27 @@ public function testGetMetadataForSingleClass(): void
         self::assertTrue($cmMap1->hasField('name'));
     }
 
+    public function testUsingIdentityWithAPlatformThatDoesNotSupportIdentityColumnsIsDeprecated(): void
+    {
+        $cm = $this->createValidClassMetadata();
+        $cm->setIdGeneratorType(ClassMetadata::GENERATOR_TYPE_IDENTITY);
+        $cmf      = new ClassMetadataFactoryTestSubject();
+        $driver   = $this->createMock(Driver::class);
+        $platform = $this->createStub(AbstractPlatform::class);
+        $platform->method('usesSequenceEmulatedIdentityColumns')->willReturn(true);
+        $platform->method('getIdentitySequenceName')->willReturn('whatever');
+        $driver->method('getDatabasePlatform')->willReturn($platform);
+        $entityManager = $this->createEntityManager(
+            new MetadataDriverMock(),
+            new Connection([], $driver)
+        );
+        $cmf->setEntityManager($entityManager);
+        $cmf->setMetadataForClass($cm->name, $cm);
+
+        $this->expectDeprecationWithIdentifier('https://github.com/doctrine/orm/issues/8850');
+        $cmf->getMetadataFor($cm->name);
+    }
+
     public function testItThrowsWhenUsingAutoWithIncompatiblePlatform(): void
     {
         $cm1 = $this->createValidClassMetadata();