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: attr.rs
    path of file: ./repos/serde/serde_derive/src/internals
    
    the code of the file until where you have to start completion: use crate::internals::symbol::*;
use crate::internals::{ungroup, Ctxt};
use proc_macro2::{Spacing, Span, TokenStream, TokenTree};
use quote::ToTokens;
use std::borrow::Cow;
use std::collections::BTreeSet;
use std::iter::FromIterator;
use syn::meta::ParseNestedMeta;
use syn::parse::ParseStream;
use syn::punctuated::
    
fn is_option(ty: &syn::Type, elem: fn(&syn::Type) -> bool) -> bool {
    let path = match ungroup(ty) {
        syn::Type::Path(ty) => &ty.path,
        _ => {
            return false;
        }
    };
    let seg = match path.segments.last() {
        Some(seg) => seg,
        None => {
            return false;
        }
    };
    let args = match &seg.arguments {
        syn::PathArguments::AngleBracketed(bracketed) => &bracketed.args,
        _ => {
            return false;
        }
    };
    seg.ident == "Option"
        && args.len() == 1
        && match &args[0] {
            syn::GenericArgument::Type(arg) => elem(arg),
            _ => false,
        }
}