use proc_macro2::*;
use synstructure::*;

pub fn null_trace_impl(s: &Structure) -> TokenStream {
    if !super::has_attr(s, "null_trace") {
        return quote!();
    }

    let bounds = s
        .variants()
        .into_iter()
        .flat_map(|v| v.bindings())
        .map(|b| {
            let ty = &b.ast().ty;
            quote! {
                #ty: elise::raw::NullTrace
            }
        });

    s.gen_impl(quote! {
        extern crate elise;

        gen unsafe impl elise::raw::NullTrace for @Self where
            #(#bounds,)*
        { }
    })
}