Fix: Core sitemaps rendered with HTTP 404 status when no post.

src/wp-admin/includes/class-wp-site-icon.php

@@ -48,8 +48,7 @@ class WP_Site_Icon {
 		/*
 		 * App icon for Android/Chrome.
 		 *
-		 * @link https://developers.google.com/web/updates/2014/11/Support-for-theme-color-in-Chrome-39-for-Android
-		 * @link https://developer.chrome.com/multidevice/android/installtohomescreen
+		 * @link https://developer.chrome.com/blog/support-for-theme-color-in-chrome-39-for-android
 		 */
 		192,
 

src/wp-includes/sitemaps/class-wp-sitemaps.php

@@ -76,6 +76,7 @@ public function init() {
 
 		// Add additional action callbacks.
 		add_filter( 'robots_txt', array( $this, 'add_robots' ), 0, 2 );
+		add_filter( 'pre_handle_404', array( $this, 'prevent_sitemap_404' ), 10, 2 );
 	}
 
 	/**
@@ -263,4 +264,24 @@ public function add_robots( $output, $is_public ) {
 
 		return $output;
 	}
+
+	/**
+	 * Prevents core from issuing a 404 status header on valid sitemap requests
+	 * when no standard blog posts exist.
+	 *
+	 * @since 6.8.0
+	 *
+	 * @param bool     $preempt Whether to short-circuit default 404 handling.
+	 * @param WP_Query $query   The global WP_Query object.
+	 * @return bool True to preempt 404 handling if a valid sitemap route is requested, original $preempt otherwise.
+	 */
+	public function prevent_sitemap_404( $preempt, $query ) {
+		if ( $query->is_main_query() && get_query_var( 'sitemap' ) ) {
+			if ( $this->sitemaps_enabled() ) {
+				return true;
+			}
+		}
+
+		return $preempt;
+	}
 }