anchor.diff:      })
     ];
   
  -  outputs = [ "bin" "dev" "out" "man" "doc" ]
  -    ++ lib.optional pythonSupport "py"
  -    ++ lib.optional (enableStatic && enableShared) "static";
  -
     strictDeps = true;
   
  -  buildInputs = lib.optional pythonSupport python
  -    ++ lib.optional (pythonSupport && python?isPy2 && python.isPy2) gettext
  -    ++ lib.optional (pythonSupport && python?isPy3 && python.isPy3) ncurses
  -    ++ lib.optional (stdenv.isDarwin &&
  -                     pythonSupport && python?isPy2 && python.isPy2) libintl
  +  buildInputs = lib.optionals pythonSupport [
  +    python
  +  ] ++ lib.optionals (pythonSupport && python?isPy2 && python.isPy2) [
  +    gettext
  +  ] ++ lib.optionals (pythonSupport && python?isPy3 && python.isPy3) [
  +    ncurses
  +  ] ++ lib.optionals (stdenv.isDarwin && pythonSupport && python?isPy2 && python.isPy2) [
  +    libintl
  +  ] ++ lib.optionals stdenv.isFreeBSD [
       # Libxml2 has an optional dependency on liblzma.  However, on impure
       # platforms, it may end up using that from /usr/lib, and thus lack a
       # RUNPATH for that, leading to undefined references for its users.
  -    ++ lib.optional stdenv.isFreeBSD xz;
  +    xz
  +  ];
   
  -  propagatedBuildInputs = [ zlib findXMLCatalogs ]
  -    ++ lib.optional stdenv.isDarwin libiconv
  -    ++ lib.optional icuSupport icu;
  +  propagatedBuildInputs = [
  +    zlib
  +    findXMLCatalogs
  +  ] ++ lib.optionals stdenv.isDarwin [
  +    libiconv
  +  ] ++ lib.optionals icuSupport [
  +    icu
  +  ];
   
     configureFlags = [
       "--exec_prefix=$dev"
  
positive.code:     (lib.withFeatureAs pythonSupport "python" python)
    ];
  
    preConfigure = lib.optionalString (lib.versionAtLeast stdenv.hostPlatform.darwinMinVersion "11") ''
      MACOSX_DEPLOYMENT_TARGET=10.16
    '';
  
    enableParallelBuilding = true;
  
    # disable test that's problematic with newer pythons: see
    # https://mail.gnome.org/archives/xml/2017-August/msg00014.html
  
negative.code:   pname = "libxml2";
    version = "2.9.12";
  
    outputs = [ "bin" "dev" "out" "man" "doc" ]
      ++ lib.optional pythonSupport "py"
      ++ lib.optional (enableStatic && enableShared) "static";
  
    src = fetchurl {
      url = "http://xmlsoft.org/sources/${pname}-${version}.tar.gz";
      sha256 = "14hxwzmf5xqppx77z7i0ni9lpzg1a84dqpf8j8l1fvy570g6imn8";
    };
  
    patches = [
      # Upstream bugs:
      #   https://bugzilla.gnome.org/show_bug.cgi?id=789714
  