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: lib.rs
    path of file: ./repos/icu4x/utils/databake/derive/src
    
    the code of the file until where you have to start completion: // This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

//! Custom derives for `Bake`

use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use quote::quote;
use syn::{
    parse::{Parse, ParseStream},
    parse_macro_input,
    punctuated::Punctuated,
    DeriveInput, Ident, Path, PathSegment, Token,
};
use synstructure::{AddBounds, Structure};

/// This custom derive auto-implements the `Bake` trait on any given type that has public
/// fields that also implement `Bake`.
///
/// For a type `Person` defined in the module `module` of crate `bar`, this derive
/// can be used as follows:
///

    
fn bake_derive_impl(input: &DeriveInput) -> TokenStream2 {
    let mut structure = Structure::new(input);

    struct PathAttr(Punctuated<PathSegment, Token![::]>);

    impl Parse for PathAttr {
        fn parse(input: ParseStream<'_>) -> syn::parse::Result<Self> {
            let i: Ident = input.parse()?;
            if i != "path" {
                return Err(input.error(format!("expected token \"path\", found {i:?}")));
            }
            input.parse::<Token![=]>()?;
            Ok(Self(input.parse::<Path>()?.segments))
        }
    }

    let path = input
        .attrs
        .iter()
        .find(|a| a.path().is_ident("databake"))
        .expect("missing databake(path = ...) attribute")
        .parse_args::<PathAttr>()
        .unwrap()
        .0;

    let body = structure.each_variant(|vi| {
        let recursive_bakes = vi.bindings().iter().map(|b| {
            let ident = b.binding.clone();
            quote! { let #ident =  #ident.bake(env); }
        });

        let constructor = vi.construct(|_, i| {
            let ident = &vi.bindings()[i].binding;
            quote! { # #ident }
        });

        quote! {
            #(#recursive_bakes)*
            databake::quote! { #path::#constructor }
        }
    });

    structure.add_bounds(AddBounds::Fields);

    let crate_name = path.iter().next().unwrap();
    let crate_name = quote!(#crate_name).to_string();

    structure.gen_impl(quote! {
        gen impl databake::Bake for @Self {
            fn bake(&self, env: &databake::CrateEnv) -> databake::TokenStream {
                env.insert(#crate_name);
                match self {
                    #body
                }
            }
        }
    })
}