Get difference between two dates including a one-month difference when both dates are on the last day of a month regardles the actual date

DateInterval.php

<?php

namespace Org_Heigl\Date;

class DateInterval extends \DateInterval
{

    public static function fromDates(DateTimeInterface $a, DateTimeInterface $b) : \DateInterval
    { 
        $first = $a;
        $second = $b;
    
        if ($a > $b) {
            $first = $b;
            $second = $a;
        }
        
        $diff = $first->diff($second);
    
        if (
            $first->format('t') === $first->format('d') &&
            $second->format('t') === $second->format('d') 
        ) {
            $numberOfMonths = $second->format('m') - $first->format('m');
            $numberOfYears = $second->format('Y') - $first->format('Y');
            $numberOfMonths += $numberOfYears * 12;
            
            $diff->d = 0;
            $diff->y = floor($numberOfMonths/12);
            $diff->m = $numberOfMonths % 12;
        }
    
        return $diff;
    }
}