You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sync_derive.rs
    path of file: ./repos/darkfi/src/serial/derive-internal/src
    
    the code of the file until where you have to start completion: /* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2020-2024 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

//! Derive (de)serialization for enums and structs, see src/serial/derive
use proc_macro2::{Ident, Span, TokenStream};
use quote::quote;
use syn::{
    Fields, FieldsNamed, FieldsUnnamed, Index, ItemEnum, ItemStruct, WhereClause, WherePredicate,
};

use super::{contains_initialize_with, contains_skip, discriminant_map, VariantParts};

fn named_fields(
    cratename: &Ident,
    enum_ident: &Ident,
    variant_ident: &Ident,
    discriminant_value: &TokenStream,
    fields: &FieldsNamed,
) -> syn::Result<VariantParts> {
    let mut where_predicates: Vec<WherePredicate> = vec![];
    let mut variant_header = TokenStream::new();
    let mut variant_body = TokenStream::new();

    for field in &fields.named {
        if !contains_skip(&field.attrs) {
            let field_ident = field.ident.clone().unwrap();

            variant_header.extend(quote! { #field_ident, });

            let field_type = &field.ty;
            where_predicates.push(
                syn::parse2(quote! {
                    #field_type: #cratename::Encodable
                })
                .unwrap(),
            );

            variant_
    
pub fn struct_de(input: &ItemStruct, cratename: Ident) -> syn::Result<TokenStream> {
    let name = &input.ident;
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
    let mut where_clause = where_clause.map_or_else(
        || WhereClause { where_token: Default::default(), predicates: Default::default() },
        Clone::clone,
    );

    let init_method = contains_initialize_with(&input.attrs);
    let return_value = match &input.fields {
        Fields::Named(fields) => {
            let mut body = TokenStream::new();
            for field in &fields.named {
                let field_name = field.ident.as_ref().unwrap();

                let delta = if contains_skip(&field.attrs) {
                    quote! {
                        #field_name: Default::default(),
                    }
                } else {
                    let field_type = &field.ty;
                    where_clause.predicates.push(
                        syn::parse2(quote! {
                            #field_type: #cratename::Decodable
                        })
                        .unwrap(),
                    );

                    quote! {
                        #field_name: #cratename::Decodable::decode(&mut d)?,
                    }
                };
                body.extend(delta);
            }
            quote! {
                Self { #body }
            }
        }
        Fields::Unnamed(fields) => {
            let mut body = TokenStream::new();
            for _ in 0..fields.unnamed.len() {
                let delta = quote! {
                    #cratename::Decodable::decode(&mut d)?,
                };
                body.extend(delta);
            }
            quote! {
                Self( #body )
            }
        }
        Fields::Unit => {
            quote! {
                Self {}
            }
        }
    };

    if let Some(method_ident) = init_method {
        Ok(quote! {
        impl #impl_generics #cratename::Decodable for #name #ty_generics #where_clause {
            fn decode<D: std::io::Read>(mut d: D) -> ::core::result::Result<Self, std::io::Error> {
                let mut return_value = #return_value;
                return_value.#method_ident();
                Ok(return_value)
            }
        }
        })
    } else {
        Ok(quote! {
            impl #impl_generics #cratename::Decodable for #name #ty_generics #where_clause {
                fn decode<D: std::io::Read>(mut d: D) -> ::core::result::Result<Self, std::io::Error> {
                    Ok(#return_value)
                }
            }
        })
    }
}