Forward port https://www.drupal.org/node/2455677

SerialSQLStorage must implement bundle rename method.

Extend FieldItemBase as as replacement of hook_field_info, hook_field_schema and hook_field_is_empty.

It is currently designed like this in the D7 version of Serial, but makes me unsure about the model. Should the site builder be able to define the cardinality of the field (should always be 1, no ?) or define the field as not required ?
Also, it can be considered with Make serial IDs optional, so the settings could probably be replaced by a clearer configuration screen for the end user.
See #5

The schema and update hooks have to be converted.

• serial_schema
• serial_field_schema (documentation for D8)
• serial_update_7130, serial_update_7131, serial_update_7132

The module does not create any table on install. It triggers table creation while creating a field on a content type. The table created is then "serial_" suffixed with a md5 generated string 'serial_' . md5("{$entity_type}{$bundle}{$field_name}").
There was already a todo left under D7 about improving this naming convention.

function _serial_get_table_name($entity_type, $bundle, $field_name) {
  // Remember about max length of MySQL tables - 64 symbols.
  // @todo Think about improvement for this.
  return db_escape_table('serial_' . md5("{$entity_type}_{$bundle}_{$field_name}"));
}

The table columns are sid - primary key ("The atomic serial field") and uniqid - unique key ("Unique temporary allocation Id") that relies on http://php.net/manual/en/function.uniqid.php.

Storage operations should be encapsulated in a service for usage amongst the classes.
It will also allow easy implementation change.

Operations to implement (interface)

• create storage
• drop storage
• init old entities
• rename storage
• get storage name
• generate schema
• generate value

Apply Drupal coding standards.

Roughly, cleaning up of

• serial.service.yml
• Drupal\serial\SerialSQLStorage

Currently, dependending on the content translation configuration you follow (create serial field then install Content translation module), you have to uncheck translation for the serial field in admin/config/regional/content-language (or e.g. admin/structure/types/manage/article/fields/node.article.field_serial) which is probably unfair because in most use cases, the serial id should follow the entity translation concept where node id's are the same, unlike i18n in D7 (see related issue Serial Field with translated nodes).

Convert automated tests to Drupal 8

The D7 version implemented hook_field_create_instance() which is not available anymore.
It had 2 side effects

1. Create the dedicated serial table (see discussion in #2)
2. Update the existing entities instances (e.g. nodes)

hook_field_delete_instance() operations must be implemented as well.

PHPCode Sniffer with Drupal coding standards + cleaning up.
https://www.drupal.org/project/coder

The Manage display form throws "Drupal\Component\Plugin\Exception\PluginException: The plugin (integer) did not specify an instance class. in Drupal\Component\Plugin\Factory\DefaultFactory::getPluginClass() (line 79 of /var/www/drupal82/core/lib/Drupal/Component/Plugin/Factory/DefaultFactory.php)."