Fuuuuuu.java

    /**
     * Best attempt at breaking the code of arity values!  We figure out how many fixed/required parameters
     * must be supplied.  Then we figure out if we need to mark the value as optional.  Optional is indicated
     * by multiplying -1 * (fixed + 1).  Keyword args optional and rest values can indicate this optional
     * condition but only if no required keyword arguments are present.
     */
    public int arityValue() {
        int oneForKeywords = requiredKwargs > 0 ? 1 : 0;
        int fixedValue = pre() + post() + oneForKeywords;
        boolean hasOptionalKeywords = kwargs - requiredKwargs > 0;

        if (opt() > 0 || rest() != Rest.NONE || (hasOptionalKeywords || restKwargs()) && oneForKeywords == 0) {
            return -1 * (fixedValue + 1);
        }

        return fixedValue;
    }