Encode/Decode tuple structs

[evnu]

As mentioned here by @davydog187:

This also brings up another issue, as far as I can tell, tuple structs and newtypes are not encodeable/decodeable

So the following should be possible:

#[derive(NifTuple)]
pub struct Newtype(i64);

#[derive(NifTuple)]
pub struct TupleStruct(i64, i64, i64);

#[derive(NifRecord)]
#[tag = "newtype"]
pub struct Newtype(i64);

#[derive(NifRecord)]
#[module = "tuplestruct"]
pub struct TupleStruct(i64, i64, i64);

[evnu]

While implementing this, I found a handy way to debug the quote output. This might be interesting to others as well:

#[proc_macro_derive(NifTuple, attributes(rustler))]
pub fn nif_tuple(input: TokenStream) -> TokenStream {
    let ast = syn::parse(input).unwrap();
    let tokens: TokenStream = tuple::transcoder_decorator(&ast).into();
    panic!("{}", TokenStream::to_string(&tokens));
    tokens
}

This aborts code generation with a panic and prints the generated code.