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: index.rs
    path of file: ./repos/derive_more/impl/src
    
    the code of the file until where you have to start completion: use crate::utils::{add_where_clauses_for_new_ident, SingleFieldData, State};
use proc_macro2::TokenStream;
use quote::{format_ident, quote};
use syn::{parse::Result, DeriveInput};

/// Provides the hook to expand `#[derive(Index)]` into an implementation of `Index`
pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
    let index_type = format_ident!("__IdxT");
    let mut state =
        State::with_field_ignore(input, trait_name, trait_name.to_lowercase())?;
    state.add_trait_path_type_param(quote! { #index_type });
    let SingleFieldData {
        field,
        field_type,
        input_type,
        trait_path_with_params,
        casted_trait,
        member,
        ..
    } = state.assert_single_enabled_field();

 
    
pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
    let index_type = format_ident!("__IdxT");
    let mut state =
        State::with_field_ignore(input, trait_name, trait_name.to_lowercase())?;
    state.add_trait_path_type_param(quote! { #index_type });
    let SingleFieldData {
        field,
        field_type,
        input_type,
        trait_path_with_params,
        casted_trait,
        member,
        ..
    } = state.assert_single_enabled_field();

    let type_where_clauses = quote! {
        where #field_type: #trait_path_with_params
    };

    let new_generics = add_where_clauses_for_new_ident(
        &input.generics,
        &[field],
        &index_type,
        type_where_clauses,
        true,
    );

    let (impl_generics, _, where_clause) = new_generics.split_for_impl();
    let (_, ty_generics, _) = input.generics.split_for_impl();
    Ok(quote! {
        #[automatically_derived]
        impl #impl_generics #trait_path_with_params for #input_type #ty_generics #where_clause {
            type Output = #casted_trait::Output;

            #[inline]
            fn index(&self, idx: #index_type) -> &Self::Output {
                #casted_trait::index(&#member, idx)
            }
        }
    })
}