anchor.diff:    optionalPlugins = {
       absubmit = enableAbsubmit;
       acousticbrainz = enableAcousticbrainz;
  +    aura = enableAura;
       badfiles = enableBadfiles;
       beatport = enableBeatport;
       bpsync = enableBpsync;
  
positive.code:   # unstable does not require bs1770gain[2].
    # [1]: https://discourse.beets.io/t/forming-a-beets-core-team/639
    # [2]: https://github.com/NixOS/nixpkgs/pull/90504
    version = "unstable-2021-01-29";
  
    src = fetchFromGitHub {
      owner = "beetbox";
      repo = "beets";
      rev = "04ea754d00e2873ae9aa2d9e07c5cefd790eaee2";
      sha256 = "sha256-BIa3hnOsBxThbA2WCE4q9eaFNtObr3erZBBqobVOSiQ=";
    };
  
    propagatedBuildInputs = [
  
negative.code:     pythonPackages.confuse
      pythonPackages.mediafile
      gobject-introspection
    ] ++ lib.optional enableAbsubmit         essentia-extractor
      ++ lib.optional enableAcoustid         pythonPackages.pyacoustid
      ++ lib.optional enableBeatport         pythonPackages.requests_oauthlib
      ++ lib.optional (enableFetchart
                    || enableDeezer
                    || enableEmbyupdate
                    || enableKodiupdate
                    || enableLoadext
                    || enablePlaylist
                    || enableSubsonicplaylist
                    || enableSubsonicupdate
                    || enableAcousticbrainz) pythonPackages.requests
      ++ lib.optional enableCheck            beetsExternalPlugins.check
      ++ lib.optional enableConvert          ffmpeg
      ++ lib.optional enableDiscogs          pythonPackages.discogs_client
      ++ lib.optional enableKeyfinder        keyfinder-cli
      ++ lib.optional enableLastfm           pythonPackages.pylast
      ++ lib.optional enableMpd              pythonPackages.mpd2
      ++ lib.optional enableSonosUpdate      pythonPackages.soco
      ++ lib.optional enableThumbnails       pythonPackages.pyxdg
      ++ lib.optional (enableAura
                    || enableWeb)            pythonPackages.flask
      ++ lib.optional enableAlternatives     beetsExternalPlugins.alternatives
      ++ lib.optional enableCopyArtifacts    beetsExternalPlugins.copyartifacts
      ++ lib.optional enableExtraFiles       beetsExternalPlugins.extrafiles
    ;
  
    buildInputs = [
  