anchor.diff: -{ lib, stdenv, fetchFromGitHub
  -, meson, ninja, pkg-config, python3, sphinx
  -, acl, curl, fuse, libselinux, udev, xz, zstd
  +{ lib
  +, stdenv
  +, fetchFromGitHub
  +, meson
  +, ninja
  +, pkg-config
  +, python3
  +, sphinx
  +, acl
  +, curl
  +, fuse
  +, libselinux
  +, udev
  +, xz
  +, zstd
   , fuseSupport ? true
   , selinuxSupport ? true
   , udevSupport ? true
  -, glibcLocales, rsync
  +, glibcLocales
  +, rsync
   }:
   
   stdenv.mkDerivation {
  
positive.code: 
    PKG_CONFIG_UDEV_UDEVDIR = "lib/udev";
    mesonFlags = lib.optionals (!fuseSupport) [ "-Dfuse=false" ]
                 ++ lib.optionals (!udevSupport) [ "-Dudev=false" ]
                 ++ lib.optionals (!selinuxSupport) [ "-Dselinux=false" ];
  
    doCheck = true;
    preCheck = ''
  
negative.code: 
    meta = with lib; {
      description = "Content-Addressable Data Synchronizer";
      homepage = "https://github.com/systemd/casync";
      license = licenses.lgpl21;
      platforms = platforms.linux;
      maintainers = with maintainers; [ flokli ];
    };
  }
  