Get all the functions registered to a specific WordPress hook

get-functions-for-hook.php

<?php
function debug_get_functions_for_hook( $hook ) {
	global $wp_filter;
	
	if( ! isset( $wp_filter[$hook] ) )
		return;
	
	$functions = array();
	foreach( (array) $wp_filter[$hook] as $key => $actions ) {
		//$functions = array_merge( $functions,  $actions );
		$functions['priority_' . $key] = array_keys( $actions );
	}
	ksort( $functions );
	return $functions;
}