anchor.diff:      pkgs.fetchzip {
         inherit
           name
  +        multihash
           sha256
           version;
         url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz";
  
positive.code:     { owner
      , repo
      , rev
      , sha256
      , version ? null
      , name ? "${repo}-${rev}"
  
negative.code:     { owner
      , repo
      , rev
      , multihash ? ""
      , sha256
      , version ? null
      , name ? "${repo}-${rev}"
  