WordPress Snippet for changing the RSS Feed GUID after a significant post update

change-guid-on-update.php

<?php
/**
 * Plugin Name:  Change RSS Feed GUID on update
 * Plugin URI:
 * Description:  Change the RSS Feed GUID after a significant post update
 * Author:       Johannes Kinast <johannes@travel-dealz.de>
 * Author URI:   https://go-around.de
 * Version:     1.0.0
 */
namespace Feed_Guid;

function check_post_update( $post_id, $post_after, $post_before ) {


	$timestamp_before = strtotime( $post_before->post_date );
	$timestamp_after = strtotime( $post_after->post_date );

	// Check if Post Date changed
	if ( $timestamp_before >= $timestamp_after ) {
		return;
	}

	// Check is Post Status is publish and if the Post Date changed significant
	if ( 'publish' === $post_after->post_status && 60*60*24 < $timestamp_after - $timestamp_before ) {

		// Find lates Revision
		if ( $latest_revision = array_shift( wp_get_post_revisions( $post_id ) ) ) {

			// Update _last_update_id to the latest revision ID
			update_post_meta( $post_id, '_last_update_id', $latest_revision->ID );

		}

	}

}
add_action( 'post_updated', __NAMESPACE__ . '\check_post_update', 10, 3 );

function feed_guid( $guid, $id ) {

	// Check if current query is for a feed
	if( ! is_feed() ) {
		return $guid;
	}

	// Get the last id
	if ( $last_id = get_metadata( 'post', $id, '_last_update_id', true ) ) {

		// Add the last id
		$guid .= '#' . (int) $last_id;

	}

	return $guid;
}
add_filter( 'the_guid', __NAMESPACE__ . '\feed_guid', 10, 2 );