`ParseCallbacks::field_visibility` is not called for new type aliases

[nyurik]

Given a header file

typedef const char *  VCL_STRING;

I would like to create a new alias type:

let bindings = bindgen::Builder::default()
    .header("src/wrapper.h")
    .parse_callbacks(Box::new(my_callbacks))
    .new_type_alias("VCL_STRING")
    .generate();

The above code generates this Rust code:

pub struct VCL_STRING(pub *const ::std::ffi::c_char);

My my_callbacks instance implements field_visibility callback, but it never gets called for the VCL_STRING type - thus I have no way for the field to be created as private or crate-public.