message: Document DepFingerprint
diff: @@ -125,6 +125,10 @@ pub fn prepare_target<'a, 'cfg>(
  ))
  }
  +/// A compilation unit dependency has a fingerprint that is comprised of:
  +/// * its package id
  +/// * its extern crate name
  +/// * its calculated fingerprint for the dependency
  type DepFingerprint = (String, String, Arc<Fingerprint>);
  /// A fingerprint can be considered to be a "short string" representing the
  