Dynamically recommend 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.

Author: greg0ire

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;

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;
@@ -616,6 +617,13 @@ private function determineIdGeneratorStrategy(AbstractPlatform $platform): int
             }
         }
 
+        $nonIdentityDefaultStrategy = self::NON_IDENTITY_DEFAULT_STRATEGY;
+
+        // DBAL 3
+        if (method_exists($platform, 'getIdentitySequenceName')) {
+            $nonIdentityDefaultStrategy[Platforms\PostgreSQLPlatform::class] = ClassMetadata::GENERATOR_TYPE_SEQUENCE;
+        }
+
         foreach (self::NON_IDENTITY_DEFAULT_STRATEGY as $platformFamily => $strategy) {
             if (is_a($platform, $platformFamily)) {
                 return $strategy;