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: option_as_ref_deref.rs
    path of file: ./repos/rust-clippy/tests/ui
    
    the code of the file until where you have to start completion: #![allow(unused, clippy::redundant_clone, clippy::useless_vec)]
#![warn(clippy::option_as_ref_deref)]

use std::ffi::{CString, OsString};
use std::ops::{Deref, DerefMut};
use std::path::PathBuf;

fn main() {
    let mu
    
fn main() {
    let mut opt = Some(String::from("123"));

    let _ = opt.clone().as_ref().map(Deref::deref).map(str::len);

    #[rustfmt::skip]
    let _ = opt.clone()
        .as_ref().map(
            Deref::deref
        )
        .map(str::len);

    let _ = opt.as_mut().map(DerefMut::deref_mut);

    let _ = opt.as_ref().map(String::as_str);
    let _ = opt.as_ref().map(|x| x.as_str());
    let _ = opt.as_mut().map(String::as_mut_str);
    let _ = opt.as_mut().map(|x| x.as_mut_str());
    let _ = Some(CString::new(vec![]).unwrap()).as_ref().map(CString::as_c_str);
    let _ = Some(OsString::new()).as_ref().map(OsString::as_os_str);
    let _ = Some(PathBuf::new()).as_ref().map(PathBuf::as_path);
    let _ = Some(Vec::<()>::new()).as_ref().map(Vec::as_slice);
    let _ = Some(Vec::<()>::new()).as_mut().map(Vec::as_mut_slice);

    let _ = opt.as_ref().map(|x| x.deref());
    let _ = opt.clone().as_mut().map(|x| x.deref_mut()).map(|x| x.len());

    let vc = vec![String::new()];
    let _ = Some(1_usize).as_ref().map(|x| vc[*x].as_str()); // should not be linted

    let _: Option<&str> = Some(&String::new()).as_ref().map(|x| x.as_str()); // should not be linted

    let _ = opt.as_ref().map(|x| &**x);
    let _ = opt.as_mut().map(|x| &mut **x);

    // Issue #5927
    let _ = opt.as_ref().map(std::ops::Deref::deref);
}