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: config_doc.rs
    path of file: ./repos/risingwave/src/common/proc_macro/src
    
    the code of the file until where you have to start completion: // Copyright 2024 RisingWave Labs
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use 
    
pub fn generate_config_doc_fn(input: DeriveInput) -> proc_macro2::TokenStream {
    let mut doc = StructFieldDocs::new();

    let struct_name = input.ident;
    match input.data {
        Data::Struct(ref data) => doc.extract_field_docs(data),
        _ => panic!("This macro only supports structs"),
    };

    let vec_fields = doc.token_vec_fields();
    let call_nested_fields = doc.token_call_nested_fields();
    quote! {
        impl #struct_name {
            pub fn config_docs(name: String, docs: &mut std::collections::BTreeMap<String, Vec<(String, String)>>) {
                docs.insert(name.clone(), #vec_fields);
                #call_nested_fields;
            }
        }
    }
}