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: env.rs
    path of file: ./repos/nextest/nextest-runner/src/cargo_config
    
    the code of the file until where you have to start completion: // Copyright (c) The nextest Contributors
// SPDX-License-Identifier: MIT OR Apache-2.0

use super::{CargoConfigSource, CargoConfigs, DiscoveredConfig};
use camino::{Utf8Path, Utf8PathBuf};
use std::{
    collections::{btree_map::Entry, BTreeMap, BTreeSet},
    ffi::OsString,
    process::Command,
};

/// Environment variables to set when running tests.
#[derive(Clone, Debug)]
pub struct EnvironmentMap {
    map: BTreeMap<imp::EnvKey, CargoEnvironmentVariable>,
}

impl EnvironmentMap {
    /// Crea
    
        fn cmp(&self, other: &Self) -> cmp::Ordering {
            unsafe {
                let result = CompareStringOrdinal(
                    self.utf16.as_ptr(),
                    self.utf16.len() as _,
                    other.utf16.as_ptr(),
                    other.utf16.len() as _,
                    1, /* ignore case */
                );
                match result {
                    CSTR_LESS_THAN => cmp::Ordering::Less,
                    CSTR_EQUAL => cmp::Ordering::Equal,
                    CSTR_GREATER_THAN => cmp::Ordering::Greater,
                    // `CompareStringOrdinal` should never fail so long as the parameters are correct.
                    _ => panic!(
                        "comparing environment keys failed: {}",
                        std::io::Error::last_os_error()
                    ),
                }
            }
        }