anchor.diff:  { fetchurl
  +, fetchpatch
   , stdenv
   , perl
   , libxml2
  
positive.code: 
  
  let
    version = "2.4.0";
    sha256 = "02baa90f04da41e04b6c18eedfda53110c45ae943d4e65050f6d202f7de07d29";
  in stdenv.mkDerivation rec {
    name = "postgis-${version}";
  
  
negative.code:     inherit sha256;
    };
  
    patches = [
      (fetchpatch {
        url = "https://trac.osgeo.org/postgis/changeset/16417?format=diff&new=16417";
        name = "json-c-0.13.patch";
        sha256 = "1hk2fh4nsvq76ksi7z4shlgj7fik6ac3sjsb0khsypsjfhz7ic8z";
        stripLen = 3;
        extraPrefix = "";
        excludes = [ "NEWS" ];
      })
    ];
  
    # don't pass these vars to the builder
    removeAttrs = ["sql_comments" "sql_srcs"];
  
    preInstall = ''
      mkdir -p $out/bin
    '';
  
    # create aliases for all commands adding version information
    postInstall = ''
  