New config schema data type: machine_name

A new config schema data type, called machine_name, has been added to core. As the name suggests, this constraint can be used to indicate that not just any string is allowed, but a string shaped like a machine name.

The default validation constraints can be found in the definition of the new machine_name data type:

# Machine-readable identifier that can only contain certain characters.
machine_name:
  type: string
  label: 'Machine name'
  constraints:
    Regex: '/^[a-z0-9_]+$/'
    Length:
      max: 64

(Note that this did not add a new MachineName validation constraint because that is not flexible enough — unfortunately not all machine names are alike!)

How to use?

Generally speaking:

Before

   mapping:
     id:
       type: string
       label: 'ID'

After

   mapping:
     id:
       type: machine_name
       label: 'ID'

Non-standard machine names

And cases where the machine name has a different set of allowed characters or a different maximum length can then override it:

Specifying a machine_name max length other than 64

media.type.*:
  type: config_entity
  label: 'Media type'
  mapping:
    id:
      type: machine_name
      label: 'Machine name'
      constraints:
        Length:
          # Media type IDs are specifically limited to 32 characters.
          # @see \Drupal\media\MediaTypeForm::form()
          max: 32

Specifying a machine_name that allows something else than alphanumeric characters & underscores

system.menu.*:
  type: config_entity
  label: 'Menu'
  mapping:
    id:
      type: machine_name
      label: 'ID'
      # Menu IDs are specifically limited to 32 characters, and allow dashes but not
      # underscores.
      # @see \Drupal\menu_ui\MenuForm::form()
      constraints:
        Regex: '/^[a-z0-9-]+$/'
        Length:
          max: 32