Add default_template_part_areas and default_template_types to site index endpoint

src/wp-admin/edit-form-blocks.php

@@ -269,10 +269,6 @@ static function ( $classes ) {
 	}
 }
 
-if ( wp_is_block_theme() && $editor_settings['supportsTemplateMode'] ) {
-	$editor_settings['defaultTemplatePartAreas'] = get_allowed_block_template_part_areas();
-}
-
 /**
  * Scripts
  */

src/wp-admin/site-editor.php

@@ -61,8 +61,6 @@ static function ( $classes ) {
 	'siteUrl'                   => site_url(),
 	'postsPerPage'              => get_option( 'posts_per_page' ),
 	'styles'                    => get_block_editor_theme_styles(),
-	'defaultTemplateTypes'      => $indexed_template_types,
-	'defaultTemplatePartAreas'  => get_allowed_block_template_part_areas(),
 	'supportsLayout'            => wp_theme_has_theme_json(),
 	'supportsTemplatePartsMode' => ! wp_is_block_theme() && current_theme_supports( 'block-template-parts' ),
 );

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -1402,6 +1402,14 @@ public function get_index( $request ) {
 			}
 		}
 
+		if ( rest_is_field_included( 'default_template_part_areas', $fields ) ) {
+			$this->add_default_template_part_areas_to_index( $response );
+		}
+
+		if ( rest_is_field_included( 'default_template_types', $fields ) ) {
+			$this->add_default_template_types_to_index( $response );
+		}
+
 		/**
 		 * Filters the REST API root index data.
 		 *
@@ -1481,6 +1489,34 @@ protected function add_site_icon_to_index( WP_REST_Response $response ) {
 		$response->data['site_icon_url'] = get_site_icon_url();
 	}
 
+	/**
+	 * Exposes the default template part areas through the WordPress REST API.
+	 *
+	 * @since 6.8.0
+	 *
+	 * @param WP_REST_Response $response REST API response.
+	 */
+	protected function add_default_template_part_areas_to_index( WP_REST_Response $response ) {
+		$response->data['default_template_part_areas'] = get_allowed_block_template_part_areas();
+	}
+
+	/**
+	 * Exposes the default template types through the WordPress REST API.
+	 *
+	 * @since 6.8.0
+	 *
+	 * @param WP_REST_Response $response REST API response.
+	 */
+	protected function add_default_template_types_to_index( WP_REST_Response $response ) {
+		$indexed_template_types = array();
+		foreach ( get_default_block_template_types() as $slug => $template_type ) {
+			$template_type['slug']    = (string) $slug;
+			$indexed_template_types[] = $template_type;
+		}
+
+		$response->data['default_template_types'] = $indexed_template_types;
+	}
+
 	/**
 	 * Exposes an image through the WordPress REST API.
 	 * This is used for fetching this information when user has no rights

tests/phpunit/tests/rest-api/rest-server.php

@@ -1358,6 +1358,82 @@ public function data_get_index_should_return_site_icon_and_site_logo_fields() {
 		);
 	}
 
+	/**
+	 * Test that the "get_index" method doesn't include the default_template_part_areas
+	 * and default_template_types fields by default.
+	 * @ticket 62574
+	 *
+	 * @covers WP_REST_Server::get_index
+	 */
+	public function test_get_index_should_not_include_default_template_part_areas_and_default_template_types() {
+		$server  = new WP_REST_Server();
+		$request = new WP_REST_Request( 'GET', '/' );
+		$index   = $server->dispatch( $request );
+		$data    = $index->get_data();
+
+		$this->assertArrayNotHasKey( 'default_template_types', $data, 'The "default_template_types" field is missing in the response.' );
+		$this->assertArrayNotHasKey( 'default_template_part_areas', $data, 'The "default_template_part_areas" field is missing in the response.' );
+	}
+
+	/**
+	 * Test that the "get_index" method returns the expected default_template_part_areas
+	 * and default_template_types fields based on the specified request parameters.
+	 *
+	 * @ticket 62574
+	 *
+	 * @covers WP_REST_Server::get_index
+	 *
+	 * @dataProvider data_get_index_should_return_default_template_part_areas_and_default_template_types
+	 *
+	 * @param string $fields            List of fields to use in the request.
+	 * @param array  $expected_fields   Expected fields.
+	 * @param array  $unexpected_fields Optional. Fields that should not be in the results. Default array().
+	 */
+	public function test_get_index_should_return_default_template_part_areas_and_default_template_types( $fields, $expected_fields, $unexpected_fields = array() ) {
+		$server  = new WP_REST_Server();
+		$request = new WP_REST_Request( 'GET', '/', array() );
+		$request->set_param( '_fields', $fields );
+		$response = $server->get_index( $request )->get_data();
+
+		foreach ( $expected_fields as $expected_field ) {
+			$this->assertArrayHasKey( $expected_field, $response, "Expected \"{$expected_field}\" field is missing in the response." );
+		}
+
+		foreach ( $unexpected_fields as $unexpected_field ) {
+			$this->assertArrayNotHasKey( $unexpected_field, $response, "Response must not contain the \"{$unexpected_field}\" field." );
+		}
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array
+	 */
+	public function data_get_index_should_return_default_template_part_areas_and_default_template_types() {
+		return array(
+			'no default_template_types or default_template_part_areas fields' => array(
+				'fields'            => 'name',
+				'expected_fields'   => array(),
+				'unexpected_fields' => array( 'default_template_types', 'default_template_part_areas' ),
+			),
+			'default_template_types field'      => array(
+				'fields'            => 'default_template_types',
+				'expected_fields'   => array( 'default_template_types' ),
+				'unexpected_fields' => array( 'default_template_part_areas' ),
+			),
+			'default_template_part_areas field' => array(
+				'fields'            => 'default_template_part_areas',
+				'expected_fields'   => array( 'default_template_part_areas' ),
+				'unexpected_fields' => array( 'default_template_types' ),
+			),
+			'default_template_part_areas and default_template_types fields' => array(
+				'fields'            => 'default_template_part_areas,default_template_types',
+				'expected_fields'   => array( 'default_template_types', 'default_template_part_areas' ),
+				'unexpected_fields' => array( '' ),
+			),
+		);
+	}
+
 	public function test_get_namespace_index() {
 		$server = new WP_REST_Server();
 		$server->register_route(