Introduce On This Day widget

lib/experimental/on-this-day/on-this-day.php

@@ -0,0 +1,73 @@
+<?php
+/**
+ * Extends the native posts REST collection with an `on_this_day` query
+ * parameter that filters posts by month and day, regardless of year.
+ *
+ * The parameter accepts a `MM-DD` string. When present, the controller
+ * appends a `date_query` clause to the underlying `WP_Query`, which
+ * resolves to an efficient SQL filter on the month and day components
+ * of `post_date`.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Pattern enforced on the `on_this_day` REST parameter.
+ *
+ * Accepts months `01`-`12` and days `01`-`31`. The combination is not
+ * calendar-validated here; impossible dates simply return no results.
+ */
+const GUTENBERG_ON_THIS_DAY_PATTERN = '^(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$';
+
+/**
+ * Advertises the `on_this_day` parameter on the posts REST collection.
+ *
+ * @param array $params Collection parameters keyed by name.
+ * @return array Collection parameters with `on_this_day` appended.
+ */
+function gutenberg_on_this_day_register_collection_param( $params ) {
+	$params['on_this_day'] = array(
+		'description' => __( 'Limit response to posts published on the given month and day (MM-DD), regardless of year.', 'gutenberg' ),
+		'type'        => 'string',
+		'pattern'     => GUTENBERG_ON_THIS_DAY_PATTERN,
+	);
+
+	return $params;
+}
+add_filter( 'rest_post_collection_params', 'gutenberg_on_this_day_register_collection_param' );
+
+/**
+ * Translates the `on_this_day` REST parameter into a `date_query` clause.
+ *
+ * Skips the translation when the parameter is missing or fails the schema
+ * pattern. The schema-level validation in `rest_post_collection_params`
+ * normally catches invalid input before this filter runs, but the
+ * defensive check keeps the filter safe for callers that bypass the
+ * controller's argument validation.
+ *
+ * @param array           $args    `WP_Query` arguments built by the controller.
+ * @param WP_REST_Request $request REST request being handled.
+ * @return array `WP_Query` arguments, extended with a `date_query` clause when applicable.
+ */
+function gutenberg_on_this_day_apply_query( $args, $request ) {
+	$value = $request['on_this_day'] ?? null;
+
+	if ( ! is_string( $value ) || ! preg_match( '/' . GUTENBERG_ON_THIS_DAY_PATTERN . '/', $value ) ) {
+		return $args;
+	}
+
+	[ $month, $day ] = array_map( 'intval', explode( '-', $value ) );
+
+	if ( ! isset( $args['date_query'] ) || ! is_array( $args['date_query'] ) ) {
+		$args['date_query'] = array();
+	}
+
+	$args['date_query'][] = array(
+		'month' => $month,
+		'day'   => $day,
+	);
+
+	return $args;
+}
+
+add_filter( 'rest_post_query', 'gutenberg_on_this_day_apply_query', 10, 2 );

lib/load.php

@@ -240,4 +240,5 @@ function gutenberg_is_experiment_enabled( $name ) {
 	require __DIR__ . '/experimental/dashboard-widgets/widget-types.php';
 	require __DIR__ . '/experimental/dashboard-widgets/dashboard-layout.php';
 	require __DIR__ . '/experimental/dashboard-widgets/default-layout-seed.php';
+	require __DIR__ . '/experimental/on-this-day/on-this-day.php';
 }

phpunit/experimental/on-this-day/on-this-day-test.php

@@ -0,0 +1,158 @@
+<?php
+/**
+ * Tests for the on_this_day REST parameter that extends the posts collection.
+ *
+ * @package gutenberg
+ */
+class On_This_Day_Test extends WP_UnitTestCase {
+
+	/**
+	 * REST route under test.
+	 */
+	const ROUTE = '/wp/v2/posts';
+
+	/**
+	 * Subscriber id with `read` capability.
+	 *
+	 * @var int
+	 */
+	protected static $subscriber_id;
+
+	/**
+	 * Fixture post ids keyed by intent.
+	 *
+	 * @var array<string, int>
+	 */
+	protected static $post_ids = array();
+
+	public static function wpSetUpBeforeClass( $factory ) {
+		self::$subscriber_id = $factory->user->create( array( 'role' => 'subscriber' ) );
+
+		self::$post_ids['oldest_may_11'] = $factory->post->create(
+			array(
+				'post_status' => 'publish',
+				'post_date'   => '2018-05-11 10:00:00',
+				'post_title'  => 'Oldest May 11',
+			)
+		);
+		self::$post_ids['newer_may_11']  = $factory->post->create(
+			array(
+				'post_status' => 'publish',
+				'post_date'   => '2020-05-11 10:00:00',
+				'post_title'  => 'Newer May 11',
+			)
+		);
+		self::$post_ids['other_day']     = $factory->post->create(
+			array(
+				'post_status' => 'publish',
+				'post_date'   => '2019-07-04 10:00:00',
+				'post_title'  => 'Independence Day',
+			)
+		);
+	}
+
+	public function set_up() {
+		parent::set_up();
+		wp_set_current_user( self::$subscriber_id );
+	}
+
+	public function tear_down() {
+		wp_set_current_user( 0 );
+		parent::tear_down();
+	}
+
+	public function test_collection_param_is_advertised_in_schema() {
+		$routes = rest_get_server()->get_routes();
+		$this->assertArrayHasKey( self::ROUTE, $routes );
+
+		$get_route_args = null;
+		foreach ( $routes[ self::ROUTE ] as $route_handler ) {
+			if ( in_array( 'GET', (array) $route_handler['methods'], true ) || ! empty( $route_handler['methods']['GET'] ) ) {
+				$get_route_args = $route_handler['args'];
+				break;
+			}
+		}
+
+		$this->assertNotNull( $get_route_args );
+		$this->assertArrayHasKey( 'on_this_day', $get_route_args );
+		$this->assertSame( 'string', $get_route_args['on_this_day']['type'] );
+		$this->assertSame( GUTENBERG_ON_THIS_DAY_PATTERN, $get_route_args['on_this_day']['pattern'] );
+	}
+
+	public function test_filter_returns_only_posts_matching_month_day() {
+		$request = new WP_REST_Request( 'GET', self::ROUTE );
+		$request->set_param( 'on_this_day', '05-11' );
+		$request->set_param( 'orderby', 'date' );
+		$request->set_param( 'order', 'asc' );
+
+		$response = rest_do_request( $request );
+
+		$this->assertSame( 200, $response->get_status() );
+
+		$ids = array_column( $response->get_data(), 'id' );
+		sort( $ids );
+
+		$expected = array( self::$post_ids['oldest_may_11'], self::$post_ids['newer_may_11'] );
+		sort( $expected );
+
+		$this->assertSame( $expected, $ids );
+	}
+
+	public function test_orderby_ascending_returns_oldest_match_first() {
+		$request = new WP_REST_Request( 'GET', self::ROUTE );
+		$request->set_param( 'on_this_day', '05-11' );
+		$request->set_param( 'orderby', 'date' );
+		$request->set_param( 'order', 'asc' );
+		$request->set_param( 'per_page', 1 );
+
+		$response = rest_do_request( $request );
+
+		$this->assertSame( 200, $response->get_status() );
+
+		$data = $response->get_data();
+		$this->assertCount( 1, $data );
+		$this->assertSame( self::$post_ids['oldest_may_11'], $data[0]['id'] );
+	}
+
+	public function test_no_match_returns_empty_collection() {
+		$request = new WP_REST_Request( 'GET', self::ROUTE );
+		$request->set_param( 'on_this_day', '02-29' );
+
+		$response = rest_do_request( $request );
+
+		$this->assertSame( 200, $response->get_status() );
+		$this->assertSame( array(), $response->get_data() );
+	}
+
+	public function test_missing_param_returns_all_published_posts() {
+		$request = new WP_REST_Request( 'GET', self::ROUTE );
+
+		$response = rest_do_request( $request );
+
+		$this->assertSame( 200, $response->get_status() );
+
+		$ids = array_column( $response->get_data(), 'id' );
+		$this->assertContains( self::$post_ids['oldest_may_11'], $ids );
+		$this->assertContains( self::$post_ids['newer_may_11'], $ids );
+		$this->assertContains( self::$post_ids['other_day'], $ids );
+	}
+
+	public function test_invalid_format_is_rejected_with_400() {
+		$request = new WP_REST_Request( 'GET', self::ROUTE );
+		$request->set_param( 'on_this_day', '2026-05-11' );
+
+		$response = rest_do_request( $request );
+
+		$this->assertSame( 400, $response->get_status() );
+	}
+
+	public function test_query_filter_ignores_invalid_value_when_called_directly() {
+		$args    = array( 'post_type' => 'post' );
+		$request = new WP_REST_Request( 'GET', self::ROUTE );
+		$request->set_param( 'on_this_day', 'not-a-date' );
+
+		$filtered = gutenberg_on_this_day_apply_query( $args, $request );
+
+		$this->assertSame( $args, $filtered );
+	}
+}

tsconfig.json

@@ -93,7 +93,8 @@
 		{ "path": "storybook" },
 		{ "path": "test/e2e" },
 		{ "path": "test/storybook-playwright" },
-		{ "path": "test/performance" }
+		{ "path": "test/performance" },
+		{ "path": "widgets" }
 	],
 	"files": []
 }

widgets/on-this-day/components/on-this-day-view/index.ts

@@ -0,0 +1 @@
+export { OnThisDayView, type BackgroundEffect } from './on-this-day-view';