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: build.rs
    path of file: ./repos/failure/failure_derive
    
    the code of the file until where you have to start completion: use std::env;
use std::process::Command;
use std::str;
use std::str::FromStr;

fn main() {
    if rustc_has_dyn_trait() {
        println!("cargo:rustc-cfg=has_dyn_trait");
    }
}

fn rustc_has_dyn_trait() -> bool {
    let rustc = match env::var_os("RUSTC") {
        Some(rustc) => rus
    
fn rustc_has_dyn_trait() -> bool {
    let rustc = match env::var_os("RUSTC") {
        Some(rustc) => rustc,
        None => return false,
    };

    let output = match Command::new(rustc).arg("--version").output() {
        Ok(output) => output,
        Err(_) => return false,
    };

    let version = match str::from_utf8(&output.stdout) {
        Ok(version) => version,
        Err(_) => return false,
    };

    let mut pieces = version.split('.');
    if pieces.next() != Some("rustc 1") {
        return true;
    }

    let next = match pieces.next() {
        Some(next) => next,
        None => return false,
    };

    u32::from_str(next).unwrap_or(0) >= 27
}