/// any type in its output. It is a write-once cache; values are never evicted,
/// which means that references to the value can safely be returned from the
/// get() method.
-//
-// FIXME: This type does not permit retrieving &Path from a PathBuf, primarily
-// due to a lack of any obvious way to ensure that this is safe, but also not
#[derive(Debug)]
pub struct Cache(
RefCell<HashMap<