Function xdg_basedir::dirs::get_config_dirs_from_env

pub fn get_config_dirs_from_env<'a, F>(get_env_var: &'a F) -> Vec<PathBuf> where
    F: Fn(&'a str) -> Option<OsString>, 

Get the default config directories given a closure that returns the the value of an environment variable. This method allows having a custom environment.

If $XDG_CONFIG_DIRS is not set, it returns [/etc/xdg].