Assuming you mean $post->ID, you can use the post_link and post_type_link filters to append your query string. We’re using the add_query_arg() function to do this:
/**
* Modify the posts navigation WHERE clause
* to include our acceptable post types
*
* @param String $post_link - Post URL
* @param WP_Post $post - Current Post
*
* @return String
*/
function wpse375877_link_referrer( $post_link, $post ) {
// Return Early
if( is_admin() ) {
return $post_link;
}
return add_query_arg( array(
'id' => $post->ID,
'referrer' => $post_link,
) );
}
add_filter( 'post_link', 'wpse375877_link_referrer', 20, 2 );
add_filter( 'post_type_link', 'wpse375877_link_referrer', 20, 2 );
The above ensures that any WordPress functions will be given a modified post URL. Now, if we wanted to redirect any URLs missing this query string, you can use template_redirect action hook:
/**
* Redirect any items without query string
*
* @return void
*/
function wpse375877_redirect_to_referrer() {
if( ! isset( $_GET, $_GET['id'], $_GET['referrer'] ) ) {
wp_safe_redirect(
add_query_arg( array(
'id' => get_the_ID(),
'referrer' => get_permalink(),
), get_permalink() )
);
exit();
}
}
add_action( 'template_redirect', 'wpse375877_redirect_to_referrer' );
I’m not 100% sure if I should be using urlencode() on these URLs or not.