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/prisma-engines/libs/user-facing-error-macros/src
    
    the code of the file until where you have to start completion: extern crate proc_macro;

#[proc_macro_derive(SimpleUserFacingError, attributes(user_facing))]
pub fn derive_simple_user_facing_error(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = syn::parse_macro_input!(input as syn::DeriveInput);

    let data = match &input.data {
        syn::Data::Struct(data) => data,
        _ => {
            return syn::Error::new_spanned(input, "derive works only on structs")
                
    
pub fn derive_simple_user_facing_error(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = syn::parse_macro_input!(input as syn::DeriveInput);

    let data = match &input.data {
        syn::Data::Struct(data) => data,
        _ => {
            return syn::Error::new_spanned(input, "derive works only on structs")
                .to_compile_error()
                .into()
        }
    };

    if !data.fields.is_empty() {
        return syn::Error::new_spanned(&data.fields, "SimpleUserFacingError implementors cannot have fields")
            .to_compile_error()
            .into();
    }

    let UserErrorDeriveInput { ident, code, message } = match UserErrorDeriveInput::new(&input) {
        Ok(input) => input,
        Err(err) => return err.into_compile_error().into(),
    };

    proc_macro::TokenStream::from(quote::quote! {
        impl serde::Serialize for #ident {
            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
                where S: serde::Serializer
            {
                serializer.serialize_none()
            }
        }

        impl crate::SimpleUserFacingError for #ident {
            const ERROR_CODE: &'static str = #code;
            const MESSAGE: &'static str = #message;
        }
    })
}