luaur-analysis 0.1.3

Luau type checker and type inference (Rust).
Documentation 
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//! Source: `Analysis/src/OverloadResolver.cpp:147-173` (hand-ported)
use crate::enums::pack_field::PackField;
use crate::functions::flatten_type_pack::flatten_type_pack_id;
use crate::functions::is_optional::is_optional;
use crate::records::path::Path;
use crate::type_aliases::component::Component;
use crate::type_aliases::subtyping_reasonings::SubtypingReasonings;
use crate::type_aliases::type_pack_id::TypePackId;

pub fn are_unsatisfied_arguments_optional(
    reasonings: &SubtypingReasonings,
    arg_pack: TypePackId,
    func_arg_pack: TypePackId,
) -> bool {
    // If the two argument lists are incompatible solely because of the argument
    // counts, the reasonings will simply point at the argument lists
    // themselves. If the reasonings point into a pack, it's because that
    // specific argument has an incompatible type.
    if 1 != reasonings.size() {
        return false;
    }

    let just_arguments = Path::from_component(Component::PackField(PackField::Arguments));
    let reason = match reasonings.iter().next() {
        Some(r) => r,
        None => return false,
    };
    if !reason.sub_path.operator_eq(&just_arguments)
        || !reason.super_path.operator_eq(&just_arguments)
    {
        return false;
    }

    let (arg_head, _arg_tail) = flatten_type_pack_id(arg_pack);
    let (fun_arg_head, _fun_arg_tail) = flatten_type_pack_id(func_arg_pack);

    if arg_head.len() >= fun_arg_head.len() {
        return false;
    }

    for i in arg_head.len()..fun_arg_head.len() {
        if !is_optional(fun_arg_head[i]) {
            return false;
        }
    }
    true
}