Register and filter fields for DataViews/DataForm in the server

[oandregal]

Related to https://core.trac.wordpress.org/ticket/65981

We want to introduce the ability to register and extend the fields used by DataViews/DataForm in the server for any given entity.

The whole initiative is tracked in Gutenberg at ​https://github.com/WordPress/gutenberg/issues/74865

Trac ticket: https://core.trac.wordpress.org/ticket/66229
See: ​https://github.com/WordPress/gutenberg/pull/83368

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Opus 5.5
Used for: Implementation. Reviewed and edited by me.

[waneezashafiq32]

Tested PR #13911 on WordPress Playground (core-pr=13911).

Environment:

• WordPress: 7.2-alpha-20261001.231912
• PHP: 7.4
• Playground (WASM) — ​https://playground.wordpress.net/?core-pr=13911

Testing performed:

1. REST endpoint verification
   • GET /wp/v2/fields → 400 rest_missing_callback_param (kind, name required) ✅
   • GET /wp/v2/fields?kind=postType&name=page (unauthenticated) → 401 rest_cannot_read ✅
   • GET /wp/v2/fields?kind=postType&name=page (authenticated via wp.apiFetch) → 200 with empty fields ✅

2. Field registration via fields_api_init hook Registered 2 custom fields on postType/page using WP_Fields_Registry::register():
   • my_test_field (text)
   • my_second_field (integer)

Confirmed signature: register( $origin, $kind, $name, $fields[], $script_module = null )

3. REST response after registration GET /wp/v2/fields?kind=postType&name=page → { kind: 'postType', name: 'page', fields: Array(2), script_modules: Array(0) } Both fields returned correctly ✅

4. Validation
   • Calling register() with incorrect arguments (missing 'id' in field definition) produces proper _doing_it_wrong() notice ✅
   • Duplicate fields are skipped as documented ✅

Result: PR works as described. The register() method correctly stores origin as
both 'origin' and 'registeredBy' properties on each field, and the REST
controller serves them per entity.

Note: During testing, I confirmed that the fields definition parameter must be
a list of arrays (each with an 'id' key), not a single field definition. The
docblock is clear about this, but it's worth noting for anyone writing their
first registration.

Props to @oandregal for the implementation.