[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

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

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[whyisjake]

Trac ticket: https://core.trac.wordpress.org/ticket/64423