DeprecationHelper helps modules support multiple versions of core

The contributed module ecosystem has had to craft ways to provide backward compatibility between minor and major versions of Drupal core.

• Minor versions: silence runtime deprecations triggered while supporting the current major version's minor versions with security coverage.
• Major versions: prevent calling deprecated code that was removed while bridging support with the latest minor version of the last major version (9.5 && 10.0.)

It often looks like this:

if (version_compare(\Drupal::VERSION, '9.4', '>=')) {
  // Do the new way introduced in 9.4, and supported in 9.5 and 10.0.
}
else {
  // @phpstan-ignore-next-line
  // Call the deprecated code for 9.2 and 9.3.
}

This is painful to copy around. By adding a new Drupal\Component\Utility\DeprecationHelper utility class, any module can now call the correct code based on the provided version.

$result = DeprecationHelper::backwardsCompatibleCall(
  currentVersion: \Drupal::VERSION,
  deprecatedVersion: '10.3',
  currentCallable: fn() => Role::loadMultiple(),
  deprecatedCallable: fn() => user_roles(),
);

PHPStan's deprecation rule package can now define custom deprecation scopes (see https://github.com/phpstan/phpstan-deprecation-rules/pull/99.) The phpstan-drupal package can then consider this as a deprecated scope, removing the need for @phpstan-ignore-next-line throughout backward compatibility layer code. This will be available soon as we work towards Drupal 11 readiness.

Drupal rector support was merged into main in september 2023.