Editor: Register the core entity fields on the server

Gruntfile.js

@@ -697,7 +697,7 @@ module.exports = function(grunt) {
 				src: 'vendor/composer/ca-bundle/res/cacert.pem',
 				dest: SOURCE_DIR + 'wp-includes/certificates/ca-bundle.crt'
 			},
-			// Gutenberg PHP infrastructure files (routes.php, pages.php, constants.php, pages/, core actions).
+			// Gutenberg PHP infrastructure files (routes.php, pages.php, constants.php, pages/, core actions, core fields).
 			'gutenberg-php': {
 				options: {
 					process: function( content ) {
@@ -718,6 +718,8 @@ module.exports = function(grunt) {
 						'pages/**/*.php',
 						// The actions Core registers through the entity actions API.
 						'scripts/core-actions/**/*.php',
+						// The fields Core registers through the entity fields API.
+						'scripts/core-fields/**/*.php',
 					],
 					dest: SOURCE_DIR + 'wp-includes/build/',
 				} ],

src/wp-includes/entity-fields.php

@@ -19,7 +19,9 @@
  * Fields can also be declared as files, grouped in a field collection, which
  * a `wp_entity_fields_api_init` callback registers with
  * {@see wp_register_entity_field_collection()}. A collection is for a single
- * entity.
+ * entity. WordPress core registers its own fields this way, from
+ * packages/core-fields: the defaults every post type derives from its
+ * supports in code, the fields of single post types as collections.
  *
  * The registered fields are exposed by the `/wp/v2/entity-fields` REST API
  * route, see {@see WP_REST_Entity_Fields_Controller}.

src/wp-settings.php

@@ -257,6 +257,9 @@
 if ( file_exists( ABSPATH . WPINC . '/build/scripts/core-actions/index.php' ) ) {
 	require ABSPATH . WPINC . '/build/scripts/core-actions/index.php';
 }
+if ( file_exists( ABSPATH . WPINC . '/build/scripts/core-fields/index.php' ) ) {
+	require ABSPATH . WPINC . '/build/scripts/core-fields/index.php';
+}
 require ABSPATH . WPINC . '/taxonomy.php';
 require ABSPATH . WPINC . '/class-wp-taxonomy.php';
 require ABSPATH . WPINC . '/class-wp-term.php';

tests/phpunit/tests/entity-fields/base.php

@@ -27,12 +27,14 @@ abstract class WP_Entity_Fields_UnitTestCase extends WP_UnitTestCase {
 	 * Sets up each test.
 	 *
 	 * Registers the fixture defaults, see register_default_fields(), at
-	 * priority 0, before the callbacks of the tests, and resets the registry
-	 * so its next read fires `wp_entity_fields_api_init` anew.
+	 * priority 0, before the callbacks of the tests, in place of the fields
+	 * WordPress core registers, and resets the registry so its next read
+	 * fires `wp_entity_fields_api_init` anew.
 	 */
 	public function set_up() {
 		parent::set_up();
 
+		remove_action( 'wp_entity_fields_api_init', 'wp_register_core_field_collections', 0 );
 		add_action( 'wp_entity_fields_api_init', array( static::class, 'register_default_fields' ), 0 );
 		self::reset_registry();
 	}