input.pds

def_type("test") => container(virtual: "true") {
    virtual_field("tag", ref: "data", prop: "tag") => u8;
    field("data") => union("test_union", ref: "../tag") {
        variant("zero", match: "0") => u8;
        variant("one", match: "1") => container {
            field("woo") => u8;
            field("hoo") => u8;
        };
    };
};

output.js

let test_fun = function (input) {
    let count = 0;
    let type_input_0 = input;
    {
        var type_input_1 = type_input_0;
        switch (type_input_1.tag) {
            case "zero": {
                var type_input_1 = 0;
                break;
            }
            case "one": {
                var type_input_1 = 1;
                break;
            }
        }
        {
            count = count + types["u8"]["size_of"](type_input_1);
        }
        var type_input_2 = type_input_0;
        {
            switch (type_input_2.tag) {
                case "zero": {
                    var type_input_3 = type_input_2.data;
                    {
                        count = count + types["u8"]["size_of"](type_input_3);
                    }
                    break;
                }
                case "one": {
                    var type_input_4 = type_input_2.data;
                    {
                        var type_input_5 = type_input_4["woo"];
                        {
                            count = count + types["u8"]["size_of"](type_input_5);
                        }
                        var type_input_6 = type_input_4["hoo"];
                        {
                            count = count + types["u8"]["size_of"](type_input_6);
                        }
                    }
                    break;
                }
            }
        }
    }
    return count;
}