anchor.diff:  
   let
     optionalPlugins = {
  +    badfiles = enableBadfiles;
       chroma = enableAcoustid;
       discogs = enableDiscogs;
       echonest = enableEchonest;
  
positive.code: , buildPythonPackage, pythonPackages, python, imagemagick
  
  , enableAcoustid   ? true
  , enableDiscogs    ? true
  , enableEchonest   ? true
  , enableFetchart   ? true
  
negative.code:     sed -i -e '/^BASH_COMPLETION_PATHS *=/,/^])$/ {
        /^])$/i u"${completion}"
      }' beets/ui/commands.py
    '' + optionalString enableBadfiles ''
      sed -i -e '/self\.run_command(\[/ {
        s,"flac","${flac}/bin/flac",
        s,"mp3val","${mp3val}/bin/mp3val",
      }' beetsplug/badfiles.py
    '';
  
    doCheck = true;
  