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: pgp.rs
    path of file: ./repos/sn0int/src/runtime
    
    the code of the file until where you have to start completion: use crate::errors::*;

use sloppy_rfc4880::{self, Tag, Signature};
use crate::engine::ctx::State;
use crate::engine::structs::{LuaMap, LuaList, byte_array};
use crate::hlua::{self, AnyLuaValue};
use std::collections::HashSet;
use std::sync::
    
fn is_new_signing_key(seen: &mut HashSet<String>, sig: &Signature) -> bool {
    let key = if let Some(fp) = &sig.fingerprint {
        fp
    } else if let Some(keyid) = &sig.keyid {
        keyid
    } else {
        return false;
    };

    if seen.contains(key) {
        return false;
    }

    seen.insert(key.to_string());
    true
}