anchor.diff:      optionals
       optionalString
       platforms;
  -in
  -
  -let
  +
     optionalPlugins = {
       # TODO: write a generic function to detect null dependencies
       acousticbrainz =
  
positive.code: 
    testShell = "${bash}/bin/bash --norc";
    completion = "${bash-completion}/share/bash-completion/bash_completion";
  in
  
  buildPythonPackage rec {
    name = "beets-${version}";
    version = "1.3.19";
    namePrefix = "";
  
    src = fetchFromGitHub {
      owner = "sampsyo";
  
negative.code:       }
      );
  
    patches = [
      (fetchTritonPatch {
        rev = "d3fc5e59bd2b4b465c2652aae5e7428b24eb5669";
  