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: identity_from.rs
    path of file: ./repos/prusti-dev/vir-gen/src/deriver
    
    the code of the file until where you have to start completion: use quote::quote;
use syn::{parse_quote, spanned::Spanned};
use crate::{ast::PathList, helpers::unbox_type};

pub(super) fn derive(items: &mut Vec<syn::Item>, current_path: &[syn::Ident]) -> Result<(), syn::Error> {
    let mut derived_items = Vec::new();
    for item in items.iter_mut() {
        if let syn::Item::Struct(struct_item) = item {
            let mut new_attributes = Vec::new();
            let mut from_type_roots = Vec::new();
            for attribute in struct_item.attrs.drain(..) {
                if attribute.style == syn::AttrStyle::Outer && attribute.path.is_ident("derive") {
                    let paths = syn::parse2::<PathList>(attribute.tokens.clone())?.paths;
                    if paths.len() == 1 
    
pub(super) fn derive(items: &mut Vec<syn::Item>, current_path: &[syn::Ident]) -> Result<(), syn::Error> {
    let mut derived_items = Vec::new();
    for item in items.iter_mut() {
        if let syn::Item::Struct(struct_item) = item {
            let mut new_attributes = Vec::new();
            let mut from_type_roots = Vec::new();
            for attribute in struct_item.attrs.drain(..) {
                if attribute.style == syn::AttrStyle::Outer && attribute.path.is_ident("derive") {
                    let paths = syn::parse2::<PathList>(attribute.tokens.clone())?.paths;
                    if paths.len() == 1 {
                        let segments = &paths[0].segments;
                        if segments.len() == 1 {
                            if &segments[0].ident == "identity_from" {
                                if let syn::PathArguments::AngleBracketed(syn::AngleBracketedGenericArguments{args, ..}) = &segments[0].arguments {
                                    if args.len() == 1 {
                                        if let syn::GenericArgument::Type(syn::Type::Path(syn::TypePath {qself: None, path: from_type_root})) = &args[0] {
                                            from_type_roots.push(from_type_root.clone());
                                            continue;
                                        }else {
                                            return Err(syn::Error::new(segments[0].span(), "the argument should be a path"));
                                        }
                                    } else {
                                        return Err(syn::Error::new(segments[0].span(), "wrong number of arguments"));
                                    }
                                } else {
                                    return Err(syn::Error::new(segments[0].span(), "wrong path argument"));
                                }
                            }
                        }
                    }
                }
                new_attributes.push(attribute);
            }
            struct_item.attrs = new_attributes;
            for from_type_root in from_type_roots {
                let derived_item = derive_from(&struct_item, from_type_root, current_path);
                derived_items.push(derived_item);
            }
        }
    }
    items.extend(derived_items);
    Ok(())
}