PHPStan Extension: Dynamic Return Types with Value Objects

Question

Some libraries (like Doctrine) use simple stringable value-objects, like Func:

<?php

class Func {

  protected $name;
  protected $arguments;

  public function __construct($name, $arguments) {
    $this->name      = $name;
    $this->arguments = $arguments;
  }

  public function __toString() {
    return $this->name . '(' . implode(', ', $this->arguments) . ')';
  }

}

$min = new Func('MIN', ['my_field']);

echo $min; // MIN(my_field)

Would it be possible for PHPStan to use a Conditional Return Type for the __toString() method, something like:

/**
 * @return ($this->value is literal-string ? literal-string : string)
 */

If not, maybe a Dynamic Return Type could work? I have used DynamicMethodReturnTypeExtension::​getTypeFromMethodCall() before, but I'm not sure if it can remember the values that have gone into the object, either during __construct() or via other methods.

This relates to the PHPStan Doctrine Extension, where my intention is for __toString() to return the literal-string type when all the inputs to the value-object are literal-string, otherwise return a string.