WordPress Share a Draft Custom Post Type Support

wp-share-a-draft-cpt-support.php

<?php
/**
 * Plugin Name:     Share A Draft Helper
 * Plugin URI:      derweili.de
 * Description:     Add Custom Post Type Support to the Share A Draft Plugin
 * Author:          derweili
 * Author URI:      derweili.de
 * Text Domain:     share-a-draft-helper
 * Domain Path:     /languages
 * Version:         0.1.0
 */

/**
 * Add Custom Post Type to Draft Select Dropdown
 * 
 * @see https://wordpress.org/support/topic/custom-post-type-support-solution/
 */
add_filter('pre_get_posts',"sad_helper_add_cpt_to_dropdown");

function sad_helper_add_cpt_to_dropdown($query) {
   if(!is_admin()) return; 
   $screen = get_current_screen();
   if($screen->base != "posts_page_shareadraft/shareadraft") return;
   $query->set('post_type',array('post','my-custom-post-type')); // Add your post types to this array
}

/**
 * Manipulate the sql query where WordPress looks for posts.
 *
 * The Share a Draft plugin hooks in very early using the 
 * `posts_results` where WordPress only searches for the
 * default `post` post-type.
 * This can only be changed by directly manipulating the SQL WHERE clause
 */
add_filter('posts_clauses_request', function( $clauses ) {
	// only manipulate the sql query when a share-a-draft link is requested
	if( ! isset( $_GET['shareadraft'] ) ) return $clauses;

	// Change the SQL where clause
	$clauses['where'] = str_replace(
		"post_type = 'post'",
		"post_type IN ('post', 'my-custom-post-type')", // Add your post types to this where clause
		$clauses['where']
	);

	return $clauses;
}, 10, 1);