dirty_solution_func_get_args_default_params.php

<?php

class ArgsMerger
{
    /**
     * @param mixed[] $args
     * @param ReflectionMethod $reflectionMethod
     *
     * @return array
     */
    public static function mergeArgsWithDefaults($args, \ReflectionMethod $reflectionMethod)
    {
        foreach (array_slice($reflectionMethod->getParameters(), count($args)) as $param) {
            /**
             * @var ReflectionParameter $param
             */
            $args[] = $param->getDefaultValue();
        }

        return $args;
    }
}

interface ProxyCandidateInterface
{
    public function foo(string $a, string $b, string $c = 'foo');

    public function fooImproved(string $a, string $b, string $c = 'foo', int $d = 1);

    public function fooEachVar($a, $b, $c = 'foo');
}

class GeneratedProxy implements ProxyCandidateInterface
{
    public function foo(string $a, string $b, string $c = 'foo')
    {
        var_dump(func_get_args());
    }

    public function fooImproved(string $a, string $b, string $c = 'foo', int $d = 1)
    {
        var_dump(ArgsMerger::mergeArgsWithDefaults(func_get_args(), new ReflectionMethod(__CLASS__, __FUNCTION__)));
    }

    public function fooEachVar($a, $b, $c = 'foo')
    {
        var_dump([$a, $b, $c]);
    }
}

$ex = new GeneratedProxy();

echo 'foo - no output of defaults';
$ex->foo('sample', 'other');
echo 'foo - WITH output of defaults';
$ex->fooImproved('sample', 'other', '2123');
echo 'foo - Previous way before 2.2.2';
$ex->fooEachVar('sample', 'other');