some rust with a compile error

test.rs

     let is_rustc = if filename.to_string_lossy().to_lowercase() == "rustc" {
        // Sanity check that it's really rustc.
        let child = creator.clone().new_command_sync(&executable)
            .stdout(Stdio::piped())
            .stderr(Stdio::null())
            .args(&["--version"])
            .spawn().chain_err(|| {
                format!("failed to execute {:?}", executable)
            });
        let output = child.into_future().and_then(move |child| {
            child.wait_with_output()
                .chain_err(|| "failed to read child output")
        });
        Box::new(output.map(|output| {
            if output.status.success() {
                if let Ok(stdout) = String::from_utf8(output.stdout) {
                    if stdout.starts_with("rustc ") {
                        return true;
                    }
                }
            }
            false
        }))
    } else {
        future::ok(false).boxed()
    };