This module allows other modules to define changes to installable configuration in a config/modify folder.

This module will try to apply modifications whenever Drupal core would apply config from config/optional.

Modifications are defined in YAML files in the config/modify folder of your module. Files must be named <module>.<unique>.yml where <module> matches the name of your module and <unique> is a unique string (e.g. add_search_field).

The files contain two top-level keys: dependencies and items. The contents of dependencies matches Drupal core's config dependency format. items should contain a list of named config items using the Config Update Definition format from the update_helper module.

All configuration keys under items are implicit config dependencies, providing for atomic updates.

For example to add an article field to a search index:

dependencies:
  config:
    - field.field.node.article.body
items:
  search_api.index.my_search:
    expected_config: { }
    add:
      field_settings:
        article_body:
          label: Article Contents
          datasource_id: 'entity:node'
          property_path: body
          type: text
          dependencies:
            config: field.field.node.article.body

The above file will automatically add an article_body field to the my_search index when the search index exists and the body field exists on the article node type. If the search index or the field does not exist it will do nothing.