Apply Gift Aid to renewal donations

functions.php

<?php 
/**
 * If the original recurring donation opted in to Gift Aid, apply Gift Aid for
 * all renewals too.
 *
 * @param  array $args Array of arguments to create donation.
 * @return array
 */
function ed_charitable_apply_gift_aid_to_renewals( $args ) {
	// Make sure this is a renewal. 
	if ( ! array_key_exists( 'meta', $args ) || ! array_key_exists( '_renewal_donation', $args['meta'] ) ) {
		return $args;
	}
	
	// We have already set the Gift Aid. 
	if ( isset( $args['meta']['giftaid'] ) ) {
		return $args;
	}
	
	// Get the original donation.
	$original = charitable_get_donation( $args['meta']['_renewal_donation'] );
	
	// Apply Gift Aid to the renewal if it was used on the original.
	if ( $original->__get( 'giftaid' ) ) {
		$args['meta']['giftaid'] = (int) $original->__get( 'giftaid' );
	}
	
	return $args;
}

add_filter( 'charitable_donation_values', 'ed_charitable_apply_gift_aid_to_renewals' );