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/tracing/tracing-attributes/src
    
    the code of the file until where you have to start completion: use std::collections::HashSet;
use syn::{punctuated::Punctuated, Expr, Ident, LitInt, LitStr, Path, Token};

use proc_macro2::TokenStream;
use quote::{quote, quote_spanned, ToTokens};
use syn::ext::IdentExt as _;
use syn::parse::{Parse, ParseStream};

/// Arguments to `#[instrument(err(...))]` and `#[instrument(ret(...))]` which describe how the
/// return value event should be emitted.
#[derive(Clone, Default, Debug)]
pub(crate) struct EventArgs {
    
    fn to_tokens(&self, tokens: &mut TokenStream) {
        if let Some(ref value) = self.value {
            let name = &self.name;
            let kind = &self.kind;
            tokens.extend(quote! {
                #name = #kind #value
            })
        } else if self.kind == FieldKind::Value {
            // XXX(eliza): I don't like that fields without values produce
            // empty fields rather than local variable shorthand...but,
            // we've released a version where field names without values in
            // `instrument` produce empty field values, so changing it now
            // is a breaking change. agh.
            let name = &self.name;
            tokens.extend(quote!(#name = tracing::field::Empty))
        } else {
            self.kind.to_tokens(tokens);
            self.name.to_tokens(tokens);
        }
    }