fn compare_old_fingerprint(
    old_hash_path: &Path,
    new_fingerprint: &Fingerprint,
    mtime_on_use: bool
) -> CargoResult<Option<DirtyReason>>
Expand description

Reads the value from the old fingerprint hash file and compare.

If dirty, it then restores the detailed information from the fingerprint JSON file, and provides an rich dirty reason.