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/stc/crates/stc_ts_errors/src
    
    the code of the file until where you have to start completion: #![allow(incomplete_features)]
#![deny(variant_size_differences)]
#![feature(specialization)]
#![cfg_attr(not(debug_assertions), allow(unused))]

use std::{
    fmt,
    fmt::{Debug, Disp
    
    fn validate(&self, err: &Error) {
        if let Ok(var) = std::env::var("DBG_ERROR") {
            let s = format!("{:?}", err);
            if !var.is_empty() && s.contains(&var) {
                crate::debug::print_backtrace();
            }
        }

        if let ErrorKind::Errors { ref errors, .. } = &*err.inner {
            for err in errors {
                self.validate(err)
            }
            return;
        }

        let code = err.code();
        if (5000..6000).contains(&code) {
            // This is error for invalid options.
        } else if err.span().is_dummy() {
            unreachable!("Error with a dummy span found: {:?}", err)
        }
    }