Proposal: Add On This Day Widget

src/wp-admin/css/dashboard.css

@@ -1017,6 +1017,35 @@ body #dashboard-widgets .postbox form .submit {
 	top: 0;
 }
 
+/* On This Day dashboard widget */
+
+#wp_dashboard_on_this_day h3 {
+	font-weight: 600;
+}
+
+#wp_dashboard_on_this_day li {
+	margin: 0;
+	padding: 0;
+}
+
+#wp_dashboard_on_this_day ul ul {
+	margin: 0 0 0 18px;
+	padding: 0;
+	list-style: disc;
+}
+
+#wp_dashboard_on_this_day ul ul li + li {
+	margin-top: 6px;
+}
+
+#wp_dashboard_on_this_day .wp-on-this-day-widget > ul > li + li {
+	margin-top: 16px;
+}
+
+#wp_dashboard_on_this_day .wp-on-this-day-post-author {
+	color: #646970;
+}
+
 /* Browse happy box */
 
 #dashboard-widgets #dashboard_browser_nag.postbox .inside {

src/wp-admin/includes/dashboard-on-this-day.php

@@ -0,0 +1,238 @@
+<?php
+/**
+ * WordPress Dashboard "On This Day" widget.
+ *
+ * @package WordPress
+ * @subpackage Administration
+ * @since 7.1.0
+ */
+
+/**
+ * Registers the On This Day dashboard widget.
+ *
+ * Designed to be the single entry point called from the dashboard setup
+ * routine. The widget is always registered so that it remains available in
+ * Screen Options and keeps its user-customized position. When there are no
+ * matching posts, a marker class is added to the postbox so the widget can be
+ * hidden with CSS.
+ *
+ * @since 7.1.0
+ */
+function wp_dashboard_on_this_day_setup() {
+	add_filter( 'postbox_classes_dashboard_wp_dashboard_on_this_day', 'wp_dashboard_on_this_day_postbox_classes' );
+
+	wp_add_dashboard_widget(
+		'wp_dashboard_on_this_day',
+		__( 'On This Day' ),
+		'wp_dashboard_on_this_day'
+	);
+}
+
+/**
+ * Hides the On This Day postbox when there are no posts to show.
+ *
+ * Adds the core `hidden` class so the widget stays registered — preserving its
+ * Screen Options entry and user-customized position — while being hidden when
+ * empty. A user can still reveal it via Screen Options, in which case the
+ * placeholder message is shown.
+ *
+ * @since 7.1.0
+ *
+ * @param string[] $classes An array of postbox classes.
+ * @return string[] Filtered postbox classes.
+ */
+function wp_dashboard_on_this_day_postbox_classes( $classes ) {
+	if ( empty( wp_dashboard_on_this_day_get_posts() ) ) {
+		$classes[] = 'hidden';
+	}
+
+	return $classes;
+}
+
+/**
+ * Renders the On This Day dashboard widget.
+ *
+ * Outputs the matching posts grouped by publication year, newest year first.
+ *
+ * @since 7.1.0
+ */
+function wp_dashboard_on_this_day() {
+	$posts = wp_dashboard_on_this_day_get_posts();
+
+	if ( empty( $posts ) ) {
+		// Placeholder shown when a user reveals the hidden widget via Screen
+		// Options on a day with no matching posts.
+		echo '<p>' . esc_html__( 'No posts were published on this day in previous years.' ) . '</p>';
+		return;
+	}
+
+	$posts_by_year = array();
+	$post_count    = count( $posts );
+
+	foreach ( $posts as $post ) {
+		$year = get_the_date( 'Y', $post );
+
+		if ( ! isset( $posts_by_year[ $year ] ) ) {
+			$posts_by_year[ $year ] = array();
+		}
+
+		$posts_by_year[ $year ][] = $post;
+	}
+
+	/* translators: Date format for the On This Day widget date, without year. See https://www.php.net/manual/datetime.format.php */
+	$date = '<strong>' . esc_html( wp_date( _x( 'F jS', 'on this day date format' ) ) ) . '</strong>';
+	?>
+	<div class="wp-on-this-day-widget">
+		<p>
+			<?php
+			if ( 1 === $post_count ) {
+				printf(
+					/* translators: %s: Date, without year. */
+					esc_html__( 'One post has been published on %s:' ),
+					$date // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Date is escaped above.
+				);
+			} else {
+				printf(
+					esc_html(
+						/* translators: 1: Number of posts, 2: Date, without year. */
+						_n(
+							'%1$s post has been published on %2$s:',
+							'%1$s posts have been published on %2$s:',
+							$post_count
+						)
+					),
+					esc_html( number_format_i18n( $post_count ) ),
+					$date // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Date is escaped above.
+				);
+			}
+			?>
+		</p>
+		<ul>
+			<?php foreach ( $posts_by_year as $year => $year_posts ) : ?>
+				<li>
+					<h3><?php echo esc_html( $year ); ?></h3>
+					<ul>
+						<?php foreach ( $year_posts as $year_post ) : ?>
+							<?php
+							$title = get_the_title( $year_post );
+
+							if ( '' === trim( $title ) ) {
+								$title = __( '(no title)' );
+							}
+
+							$author_id   = (int) $year_post->post_author;
+							$author_name = $author_id > 0 ? (string) get_the_author_meta( 'display_name', $author_id ) : '';
+							$show_author = '' !== trim( $author_name ) && get_current_user_id() !== $author_id;
+							?>
+							<li>
+								<a href="<?php echo esc_url( get_permalink( $year_post ) ); ?>"><?php echo esc_html( $title ); ?></a>
+								<?php if ( $show_author ) : ?>
+									<?php
+									echo '<span class="wp-on-this-day-post-author">' . esc_html(
+										sprintf(
+											/* translators: %s: Post author's display name. */
+											__( 'by %s' ),
+											$author_name
+										)
+									) . '</span>';
+									?>
+								<?php endif; ?>
+							</li>
+						<?php endforeach; ?>
+					</ul>
+				</li>
+			<?php endforeach; ?>
+		</ul>
+	</div>
+	<?php
+}
+
+/**
+ * Retrieves published posts from all authors that were published on this
+ * calendar day in previous years.
+ *
+ * The date constraint matches today's month and day, combined with a
+ * `before` clause anchored to January 1 of the current year. Up to ten posts
+ * are returned; use the `wp_dashboard_on_this_day_query_args` filter to change
+ * the limit. Results are cached by WP_Query's native query caching.
+ *
+ * @since 7.1.0
+ *
+ * @return WP_Post[] Array of posts ordered by newest first.
+ */
+function wp_dashboard_on_this_day_get_posts() {
+	$today      = current_datetime();
+	$year       = (int) $today->format( 'Y' );
+	$date_query = array(
+		'relation' => 'AND',
+		array(
+			'before' => array( 'year' => $year ),
+		),
+		_wp_dashboard_on_this_day_date_query_clause( $today ),
+	);
+
+	$args = array(
+		'post_type'              => 'post',
+		'post_status'            => array( 'publish' ),
+		'posts_per_page'         => 10,
+		'ignore_sticky_posts'    => true,
+		'orderby'                => 'date',
+		'order'                  => 'DESC',
+		'no_found_rows'          => true,
+		'update_post_term_cache' => false,
+		'update_post_meta_cache' => false,
+		'date_query'             => $date_query,
+	);
+
+	/**
+	 * Filters the arguments used to query posts for the On This Day dashboard widget.
+	 *
+	 * @since 7.1.0
+	 *
+	 * @param array $args WP_Query arguments.
+	 */
+	$args = apply_filters( 'wp_dashboard_on_this_day_query_args', $args );
+
+	$query = new WP_Query( $args );
+
+	return $query->posts;
+}
+
+/**
+ * Builds the date query clause for today's anniversary date.
+ *
+ * On February 28 in a non-leap year, February 29 posts are included so
+ * leap-day anniversaries still appear.
+ *
+ * @since 7.1.0
+ * @access private
+ *
+ * @param DateTimeInterface $date Date to build the clause for.
+ * @return array Date query clause.
+ */
+function _wp_dashboard_on_this_day_date_query_clause( $date ) {
+	$month  = (int) $date->format( 'm' );
+	$day    = (int) $date->format( 'd' );
+	$clause = array(
+		'month' => $month,
+		'day'   => $day,
+	);
+
+	// Display leap day posts on Feb 28 in non leap years.
+	if (
+		28 === $day
+		&& 2 === $month
+		&& false === (bool) $date->format( 'L' )
+	) {
+		$clause = array(
+			'relation' => 'OR',
+			$clause,
+			array(
+				'month' => 2,
+				'day'   => 29,
+			),
+		);
+	}
+
+	return $clause;
+}

src/wp-admin/includes/dashboard.php

@@ -88,6 +88,13 @@ function wp_dashboard_setup() {
 		wp_add_dashboard_widget( 'dashboard_quick_press', $quick_draft_title, 'wp_dashboard_quick_press' );
 	}
 
+	// On This Day.
+	if ( ! function_exists( 'wp_dashboard_on_this_day_setup' ) ) {
+		require_once ABSPATH . 'wp-admin/includes/dashboard-on-this-day.php';
+	}
+
+	wp_dashboard_on_this_day_setup();
+
 	// WordPress Events and News.
 	wp_add_dashboard_widget( 'dashboard_primary', __( 'WordPress Events and News' ), 'wp_dashboard_events_news' );