[RFC] Posts: Introduce register_content_type() API for declarative content modeling

[whyisjake]

Summary

This is a prototype implementation of the Declarative Content Modeling RFC that introduces register_content_type() - a higher-level API for registering content types in WordPress.

Try it out

Try the demo in WordPress Playground - includes a "Books" content type with sample data.

What it does

• Registers a post type via register_post_type()
• Registers meta fields via register_post_meta() for each declared field
• Provides automatic REST API schema generation
• Supports field type validation (string, integer, number, boolean, array, object)
• Stores UI hints for potential editor/admin integrations

Example usage

register_content_type( 'book', array(
    'labels'       => array( 'name' => 'Books' ),
    'public'       => true,
    'show_in_rest' => true,
    'fields'       => array(
        'isbn' => array(
            'type'     => 'string',
            'required' => true,
            'label'    => 'ISBN',
        ),
        'published_year' => array(
            'type'  => 'integer',
            'label' => 'Published Year',
        ),
    ),
    'ui' => array(
        'editor_panel' => array(
            'title'  => 'Book Details',
            'fields' => array( 'isbn', 'published_year' ),
        ),
    ),
) );

New functions

• register_content_type() / unregister_content_type()
• content_type_exists() / get_content_type_object() / get_content_types()
• get_content_type_fields() / get_content_type_field()
• get_content_type_ui() / get_content_type_rest_schema()
• validate_content_type_values()

Files added

• src/wp-includes/class-wp-content-type.php - Core class
• src/wp-includes/content-type.php - API functions
• tests/phpunit/tests/post/wpContentType.php - Unit tests (38 tests)

Status

🚧 Work in Progress - This is an early prototype for discussion and feedback.

Test plan

• [x] All 38 unit tests pass
• [ ] Manual testing with example plugin
• [ ] REST API endpoint testing
• [ ] Editor integration testing