WordPress fork detection

wp_fork_detect.php

<?php
/**
* WordPress fork detection
*
* Check if a WordPress fork is in use. The check is a seperate function, instead of simply using the current function_exists
* in case the method of detection needs to change.
*/

function is_fork() {
	
	$fork = false;
	
	if ( function_exists( 'calmpress_version' ) ) { $fork = 'calmPress'; }		
	if ( function_exists( 'classicpress_version' ) ) { $fork = 'ClassicPress'; }

	return $fork;

}

/**
* Show fork message
*
* Display a message, if user is using a WordPress fork
*/

function fork_admin_message() {
	
	if ( false !== is_fork() ) {

		echo '<div class="notice notice-error"><p>' .  __( '[Plugin name] does not support forks of WordPress. Please disable the plugin or consider switching to WordPress.', 'sample-text-domain' ) . '</p></div>';
		
	}
}

add_action( 'admin_notices', 'fork_admin_message' );