Simplify the HTML of field.html.twig

kostask → closed merge request !7416

At DrupalCon Prague we decided that field--has-multiple-items and field--has-single-item were not communicating the correct information. We need to communicate the field cardinality in the database. When a user sees has-multiple or has-single they will connect this information what is rendered. A multivalue field can have just one entry, but in the original patch it would get a has-multiple-items class.

Just for clarity, the way field.html.twig currently works is that if it's a multivalue field - even if it only has one item in it - it gets the .field__items wrapper. If it has only one item, that item is wrapped in a div and if it has more than one item it uses ul.

The class we are intending to add here field--multiple will denote that this is a multivalue field, not how many items are in the field.
Perhaps we could add another class field--has-N-items to denote how many items we actually have.

Suggestion for classes:

  'field--name-' ~ field_name|clean_class,
  'field--type-' ~ field_type|clean_class,
  'field--label-' ~ label_display,
  multiple ? 'field--multivalue-field' : 'field--single-value-field',
  multiple ? 'field--has' ~ items|length ~ 'items'|clean_class : 'field--has-1-item',
  label_display == 'inline' ? 'clearfix',

Note: we will need to update the issue summary with new notes for the change record.