Dynamically resolve AUTO to SEQUENCE or IDENTITY

With DBAL 3.x, IDENTITY results in SERIAL.
With DBAL 4.x, it results in the standard GENERATED BY DEFAULT AS IDENTITY.

UPGRADE.md

@@ -9,12 +9,12 @@ Make sure to use the former when writing a type declaration or an `instanceof` c
 To keep PHP mapping attributes consistent, order of arguments passed to above attributes has been changed
 so `$targetEntity` is a first argument now. This change affects only non-named arguments usage.
 
-## BC BREAK: AUTO keyword for identity generation defaults to IDENTITY for PostgreSQL now
+## BC BREAK: AUTO keyword for identity generation defaults to IDENTITY for PostgreSQL when using `doctrine/dbal` 4
 
-When using the AUTO strategy to let Doctrine determine the identity generation mecehanism for
-an entity, PostgreSQL now uses IDENTITY instead of SEQUENCE. When upgrading from ORM 2.x
-and preference is on keeping the SEQUENCE based identity generation, then configure the ORM
-this way:
+When using the `AUTO` strategy to let Doctrine determine the identity generation mechanism for
+an entity, and when using `doctrine/dbal` 4, PostgreSQL now uses `IDENTITY`
+instead of `SEQUENCE`. When upgrading from ORM 2.x and preference is on keeping
+the `SEQUENCE` based identity generation, then configure the ORM this way:
 
 ```php
 use Doctrine\DBAL\Platforms\PostgreSQLPlatform;

docs/en/reference/basic-mapping.rst

@@ -329,9 +329,9 @@ defaults to the identifier generation mechanism your current database
 vendor preferred at the time that strategy was introduced:
 ``AUTO_INCREMENT`` with MySQL, sequences with PostgreSQL and Oracle and
 so on.
-We now recommend using ``IDENTITY`` for PostgreSQL, and you can achieve
-that while still using the ``AUTO`` strategy, by configuring what it
-defaults to.
+If you are using `doctrine/dbal` 4, we now recommend using ``IDENTITY``
+for PostgreSQL, and you can achieve that while still using the ``AUTO``
+strategy, by configuring what it defaults to.
 
 .. code-block:: php
 

lib/Doctrine/ORM/Mapping/ClassMetadataFactory.php

@@ -34,6 +34,7 @@
 use function in_array;
 use function is_a;
 use function is_subclass_of;
+use function method_exists;
 use function str_contains;
 use function strlen;
 use function strtolower;
@@ -616,7 +617,14 @@ private function determineIdGeneratorStrategy(AbstractPlatform $platform): int
             }
         }
 
-        foreach (self::NON_IDENTITY_DEFAULT_STRATEGY as $platformFamily => $strategy) {
+        $nonIdentityDefaultStrategy = self::NON_IDENTITY_DEFAULT_STRATEGY;
+
+        // DBAL 3
+        if (method_exists($platform, 'getIdentitySequenceName')) {
+            $nonIdentityDefaultStrategy[Platforms\PostgreSQLPlatform::class] = ClassMetadata::GENERATOR_TYPE_SEQUENCE;
+        }
+
+        foreach ($nonIdentityDefaultStrategy as $platformFamily => $strategy) {
             if (is_a($platform, $platformFamily)) {
                 return $strategy;
             }

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

@@ -9,6 +9,7 @@
 use Doctrine\DBAL\Driver;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
 use Doctrine\DBAL\Platforms\OraclePlatform;
+use Doctrine\DBAL\Platforms\PostgreSQLPlatform;
 use Doctrine\Deprecations\PHPUnit\VerifyDeprecations;
 use Doctrine\ORM\Configuration;
 use Doctrine\ORM\EntityManagerInterface;
@@ -139,6 +140,38 @@ public function testRelyingOnLegacyIdGenerationDefaultsIsOKIfItResultsInTheCurre
         $cmf->getMetadataFor($cm->name);
     }
 
+    public function testPostgresSticksWithSequencesWhenDbal3IsUsed(): void
+    {
+        if (! method_exists(AbstractPlatform::class, 'getIdentitySequenceName')) {
+            self::markTestSkipped('This test requires DBAL 3');
+        }
+
+        $cm = $this->createValidClassMetadata();
+        $cm->setIdGeneratorType(ClassMetadata::GENERATOR_TYPE_AUTO);
+        $cmf = $this->setUpCmfForPlatform(new PostgreSQLPlatform());
+        $cmf->setMetadataForClass($cm->name, $cm);
+
+        $metadata = $cmf->getMetadataFor($cm->name);
+
+        self::assertSame(ClassMetadata::GENERATOR_TYPE_SEQUENCE, $metadata->generatorType);
+    }
+
+    public function testPostgresSwitchesToIdentityColumnsWhenDbal4IsUsed(): void
+    {
+        if (method_exists(AbstractPlatform::class, 'getIdentitySequenceName')) {
+            self::markTestSkipped('This test requires DBAL 4');
+        }
+
+        $cm = $this->createValidClassMetadata();
+        $cm->setIdGeneratorType(ClassMetadata::GENERATOR_TYPE_AUTO);
+        $cmf = $this->setUpCmfForPlatform(new PostgreSQLPlatform());
+        $cmf->setMetadataForClass($cm->name, $cm);
+
+        $metadata = $cmf->getMetadataFor($cm->name);
+
+        self::assertSame(ClassMetadata::GENERATOR_TYPE_IDENTITY, $metadata->generatorType);
+    }
+
     public function testGetMetadataForThrowsExceptionOnUnknownCustomGeneratorClass(): void
     {
         $cm1 = $this->createValidClassMetadata();