Protect all child pages of a page protected by the "Protect Add-on Pages" add-on

pmpro-apply-addon-access-to-all-child-pages.php

<?php
/*
Plugin Name: Paid Memberships Pro - Protect Child Pages Add On
Plugin URI: http://www.paidmembershipspro.com/wp/pmpro-customizations/
Description: Apply protection to all child pages of a Add-on Page that's protected.
Version: .1
Author: Thomas Sjolshagen @ Stranger Studios <thomas@eighty20results.com>
Author URI: https://eighty20results.com/thomas-sjolshagen/
*/
/**
 * Apply protection of parent page to child pages.
 *
 * @param $hasaccess
 * @param $thepost
 * @param $theuser
 * @param $post_membership_levels
 * @return bool
 *
 * @since v.1
 */
function pmproap_hide_child_posts( $hasaccess, $thepost, $theuser, $post_membership_levels)
{
    global $wpdb;
    global $pmpro_inaccessible_parent;
    global $pmpro_pages;

    if (in_array($thepost->ID, $pmpro_pages)) {
        return $hasaccess;
    }

    $pmpro_inaccessible_parent = null;

    //if PMPro says false already, return false
    if (!$hasaccess)
        return false;

    //if PMPro Addon Packages is not installed, return
    if (!function_exists('pmproap_hasAccess'))
        return $hasaccess;

    // this post/page doesn't have a parent so nothing to check.
    if (empty( $thepost->post_parent ) ) {
        return $hasaccess;
    }

    if ( ! pmproap_hasAccess($theuser->ID, $thepost->post_parent) ) {
        $pmpro_inaccessible_parent = $thepost->post_parent;
        $hasaccess = false;
    }

    return $hasaccess;
}
add_filter("pmpro_has_membership_access_filter", "pmproap_hide_child_posts", 10, 4);

/**
 * Show a link to checkout for the addon package for child-posts of a Add-on protected parent page
 * @param $text
 * @return string
 */
function pmproap_pmpro_text_filter_for_child_posts($text)
{
    global $wpdb, $current_user, $post, $pmpro_currency_symbol;
    global $pmpro_inaccessible_parent;
    global $pmpro_pages;

    if (empty($post->post_parent) || ( !empty($post->post_parent) && in_array( $post->post_parent, $pmpro_pages) )) {
        error_log("No parent post configured, so exiting");
        return $text;
    }

    if ( ! pmproap_hasAccess($current_user->ID, $post->post_parent) ) {

        //which level to use for checkout link?
        $text_level_id = pmproap_getLevelIDForCheckoutLink($post->post_parent, $current_user->ID);

        //what's the price
        $pmproap_price = get_post_meta($post->post_parent, "_pmproap_price", true);

        //check for all access levels
        $all_access_levels = apply_filters("pmproap_all_access_levels", array(), $current_user->ID, $post->post_parent);

            //update text
        if (!empty($all_access_levels)) {
            $level_names = array();
            foreach ($all_access_levels as $level_id) {
                $level = pmpro_getLevel($level_id);
                $level_names[] = $level->name;
            }

            error_log("Set additional access text for all access levels");
            $text = "<p>This content requires that you purchase additional access. The price is " . $pmpro_currency_symbol . $pmproap_price . " or free for our " . pmpro_implodeToEnglish($level_names) . " members.</p>";
            $text .= "<p><a href=\"" . pmpro_url("checkout", "?level=" . $text_level_id . "&ap=" . $post->post_parent) . "\">Purchase this Content (" . pmpro_formatPrice($pmproap_price) . ")</a> <a href=\"" . pmpro_url("levels") . "\">Choose a Membership Level</a></p>";
        } elseif( !empty($text_level_id)) {
            error_log("Set additional access text for all level: {$text_level_id}");
            $text = "<p>This content requires that you purchase additional access. The price is " . pmpro_formatPrice($pmproap_price) . ".</p>";
            $text .= "<p><a href=\"" . pmpro_url("checkout", "?level=" . $text_level_id . "&ap=" . $post->post_parent) . "\">Click here to checkout</a></p>";
        }
    }

    return $text;
}
add_filter("pmpro_non_member_text_filter", "pmproap_pmpro_text_filter_for_child_posts", 15);
add_filter("pmpro_not_logged_in_text_filter", "pmproap_pmpro_text_filter_for_child_posts", 15);

This recipe is included in the blog post on "Sister Plugin for Addon Packages: Apply Parent Page’s Protection to All Child Pages" at Paid Memberships Pro here: https://www.paidmembershipspro.com/use-addon-packages-apply-parent-pages-protection-child-pages/