Introduce database driver extensions and autoload database drivers' dependencies

Extensions for database drivers

The extensions for database drivers have been added. The service for getting the list of database driver extensions is \Drupal::service('extension.list.database_driver'). The extensions are keyed by their namespace and not their driver name as can be multiple drivers for the same database. For instance we have the pgsql database driver that is provided by the core module pgsql. The module pgsql_fallback also provides a pgsql database driver. It does that for older versions of PostgreSQL that are no longer supported by Drupal.

Calling \Drupal::service('extension.list.database_driver')->get($driver_name) with the driver name is deprecated. The correct way of getting the database driver extension is by using the drivers namespace. Like: \Drupal::service('extension.list.database_driver')->get($namespace).

The added method \Drupal::service('extension.list.database_driver')->getFromDriverName($driver_name) is deprecated. The method is helper method to make the previous deprecation possible. The method returns the first available database driver extension for the given driver name.

The Drupal form install_settings_form that lives in the class Drupal\Core\Installer\Form\SiteSettingsForm must use the namespace for the driver field and using the field with the driver name is deprecated.

drupal_get_database_types()

The function drupal_get_database_types() has been deprecated and is being replaced by \Drupal::service('extension.list.database_driver')->getInstallableList();

Before:

// The drivers are keyed by their driver name.
$drivers = drupal_get_database_types();

After:

// The drivers are keyed by their namespace.
$drivers = \Drupal::service('extension.list.database_driver')->getInstallableList();

OR

// The drivers are keyed by their driver name. Will fail when multiple drivers have the same name.
$drivers = [];
foreach (\Drupal::service('extension.list.database_driver')->getInstallableList() as $driver) {
  $drivers[$driver->getDriverName()] = $driver->getInstallTasks();
}

drupal_detect_database_types()

The function drupal_detect_database_types() has been deprecated and is being replaced by \Drupal::service('extension.list.database_driver')->getInstallableList();

Before:

// The drivers are keyed by their driver name.
$drivers = drupal_detect_database_types();

After:

// The drivers are keyed by their namespace.
$drivers = \Drupal::service('extension.list.database_driver')->getInstallableList();

OR

// The drivers are keyed by their driver name. Will fail when multiple drivers have the same name.
$drivers = [];
foreach (\Drupal::service('extension.list.database_driver')->getInstallableList() as $driver) {
  $drivers[$driver->getDriverName()] = $driver->getInstallTasks()->name();
}

Drupal\Core\Database\Database::findDriverAutoloadDirectory()

The method Drupal\Core\Database\Database::findDriverAutoloadDirectory() has been deprecated and is being replaced by \Drupal::service('extension.list.database_driver')->get($namespace)->getAutoloadInfo().

Before:
$autoload_data = Drupal\Core\Database\Database::findDriverAutoloadDirectory($namespace, DRUPAL_ROOT))

After:

$autoload_data = \Drupal::service('extension.list.database_driver')->get($namespace)->getAutoloadInfo()['autoload']

// Autoload data on which the current database driver is dependent.
$autoload_data_dependencies = \Drupal::service('extension.list.database_driver')->get($namespace)->getAutoloadInfo()['dependencies']

Settings.php

During the installation process, database drivers that have dependencies will have the autoloading information for the dependencies added in the settings.php file. This is necessary to allow ensuring access to the extended classes very early during the request, before the container is actually available.

For most (> 99%) sites this will not be the case. There are at the moment only 2 database drivers that are dependent on another database driver. Those are: https://www.drupal.org/project/mysql56 and https://www.drupal.org/project/pgsql_fallback.

When a new site is created the database driver data in settings.php will have an additional key named "dependencies". That key will contain the dependency data for the database driver. Something like:

$databases['default']['default'] = [
  'driver' => 'my_driver',
  'namespace' => 'Drupal\my_module\Driver\Database\my_driver',
  'autoload' => 'modules/my_module/src/Driver/Database/my_driver/',
  'database' => 'databasename',
  'username' => 'sqlusername',
  'password' => 'sqlpassword',
  'host' => 'localhost',
  'prefix' => '',
  'dependencies' => [
    'parent_module' => [
      'namespace' => 'Drupal\parent_module',
      'autoload' => 'core/modules/parent_module/src/',
    ],
  ],
];