Function xdg_basedir::dirs::get_cache_home_from_env

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

Get the cache home directory given a closure that returns the the value of an environment variable. This method allows having a custom environment.

If $XDG_CACHE_HOME is not set, it returns $HOME/.cache.