anchor.diff:  
   let
     optionalPlugins = {
  +    badfiles = enableBadfiles;
       chroma = enableAcoustid;
       discogs = enableDiscogs;
       echonest = enableEchonest;
  
positive.code: }:
  
  assert enableAcoustid    -> pythonPackages.pyacoustid     != null;
  assert enableDiscogs     -> pythonPackages.discogs_client != null;
  assert enableEchonest    -> pythonPackages.pyechonest     != null;
  assert enableFetchart    -> pythonPackages.responses      != null;
  
negative.code:   };
  
    pluginsWithoutDeps = [
      "bench" "bpd" "bpm" "bucket" "convert" "cue" "duplicates" "embedart"
      "filefilter" "freedesktop" "fromfilename" "ftintitle" "fuzzy" "ihate"
      "importadded" "importfeeds" "info" "inline" "ipfs" "keyfinder" "lyrics"
      "mbcollection" "mbsync" "metasync" "missing" "permissions" "play"
      "plexupdate" "random" "rewrite" "scrub" "smartplaylist" "spotify" "the"
      "types" "zero"
    ];
  