anchor.diff: -{ lib, stdenv, fetchurl, libxml2, pkg-config, perl
  +{ lib, stdenv, fetchurl, libxml2, pkg-config
   , compressionSupport ? true, zlib ? null
   , sslSupport ? true, openssl ? null
   , static ? stdenv.hostPlatform.isStatic
  
positive.code: in
  
  stdenv.mkDerivation rec {
    version = "0.31.0";
    pname = "neon";
  
    src = fetchurl {
      url = "http://www.webdav.org/neon/${pname}-${version}.tar.gz";
      sha256 = "19dx4rsqrck9jl59y4ad9jf115hzh6pz1hcl2dnlfc84hc86ymc0";
    };
  
    patches = optionals stdenv.isDarwin [ ./0.29.6-darwin-fix-configure.patch ];
  
negative.code: 
    passthru = {inherit compressionSupport sslSupport;};
  
    meta = with lib; {
      description = "An HTTP and WebDAV client library";
      homepage = "https://notroj.github.io/neon/";
      changelog = "https://github.com/notroj/${pname}/blob/${version}/NEWS";
      platforms = platforms.unix;
      license = licenses.lgpl2;
    };
  