wp_check_for_changed_slugs( int $post_id, WP_Post $post, WP_Post $post_before )

Source

File: wp-includes/post.php

function wp_check_for_changed_slugs( $post_id, $post, $post_before ) {
	// Don't bother if it hasn't changed.
	if ( $post->post_name == $post_before->post_name ) {
		return;
	}

	// We're only concerned with published, non-hierarchical objects.
	if ( ! ( 'publish' === $post->post_status || ( 'attachment' === get_post_type( $post ) && 'inherit' === $post->post_status ) ) || is_post_type_hierarchical( $post->post_type ) ) {
		return;
	}

	$old_slugs = (array) get_post_meta( $post_id, '_wp_old_slug' );

	// If we haven't added this old slug before, add it now.
	if ( ! empty( $post_before->post_name ) && ! in_array( $post_before->post_name, $old_slugs, true ) ) {
		add_post_meta( $post_id, '_wp_old_slug', $post_before->post_name );
	}

	// If the new slug was used previously, delete it from the list.
	if ( in_array( $post->post_name, $old_slugs, true ) ) {
		delete_post_meta( $post_id, '_wp_old_slug', $post->post_name );
	}
}