Hello,
I'm currently updating Doctrine DBAL from version 3 to 4 on an app that uses Doctrine generated ID columns (with no strategy defined, thus using AUTO if I'm not mistaken) with PostgreSQL 17.

I suspect that the generation strategies' documentation for PostgreSQL is outdated or inaccurate, due to changes introduced in / for Doctrine DBAL 4.

Here's a more detailed report / explanation:

I initially encountered database errors about PostgreSQL's SEQUENCE, and tried tinkering with the strategy, to no avail.
I then stumbled upon the following documentation: https://github.com/doctrine/dbal/blob/4.3.x/docs/en/how-to/postgresql-identity-migration.rst

Still, something about the generation strategies' documentation confused me: the documentation claims that no matter Doctrine DBAL's version, the default (AUTO) strategy on PostgreSQL is SEQUENCE.

When tested on my app, either of these 2 lines produce the same database migrations:

#[ORM\GeneratedValue(strategy: 'IDENTITY')]
#[ORM\GeneratedValue]

ALTER TABLE my_table ALTER id DROP DEFAULT;
ALTER TABLE my_table ALTER id ADD GENERATED BY DEFAULT AS IDENTITY;

but the SEQUENCE strategy just seems to remove the DEFAULT:

#[ORM\GeneratedValue(strategy: 'SEQUENCE')]

ALTER TABLE my_table ALTER id DROP DEFAULT;

This behavior suggested that the default strategy on PostgreSQL would be IDENTITY and not SEQUENCE.

After digging into the code, it seems to be the case:

• PostgreSQL isn't listed in NON_IDENTITY_DEFAULT_STRATEGY:

  orm/src/Mapping/ClassMetadataFactory.php

  Lines 63 to 65 in 21e9fcb

  	private const NON_IDENTITY_DEFAULT_STRATEGY = [
  	Platforms\OraclePlatform::class => ClassMetadata::GENERATOR_TYPE_SEQUENCE,
  	];

• but it is set only when using DBAL 3:

  orm/src/Mapping/ClassMetadataFactory.php

  Lines 631 to 634 in 21e9fcb

  	// DBAL 3
  	if (method_exists($platform, 'getIdentitySequenceName')) {
  	$nonIdentityDefaultStrategy[Platforms\PostgreSQLPlatform::class] = ClassMetadata::GENERATOR_TYPE_SEQUENCE;
  	}

• when using DBAL 4, the previous code isn't triggered, and falls back to IDENTITY:

  orm/src/Mapping/ClassMetadataFactory.php

  Line 666 in 21e9fcb

  return ClassMetadata::GENERATOR_TYPE_IDENTITY;

• Doctrine DBAL's PostgreSQLPlatform then outputs GENERATED BY DEFAULT AS IDENTITY: https://github.com/doctrine/dbal/blob/1432ec68513bb1788d9ed4e7ace4f12f6595fb9c/src/Platforms/PostgreSQLPlatform.php#L276

Thank you for reviewing my PR, tell me if there is anything wrong / that can be improved in it 👍
Thank you for all the work you did on Doctrine!

PS : Do these documentation changes need to be backported all the way back to ORM 3.0? The initial commit that introduced this difference seems to date back to ORM 3.0 RC 1: bdc039f