anchor.diff:  
     configureFlags = [
         "--disable-manual"
  +      "--with-nghttp2=${libnghttp2}"
         ( if sslSupport then "--with-ssl=${openssl}" else "--without-ssl" )
         ( if scpSupport then "--with-libssh2=${libssh2}" else "--without-libssh2" )
         ( if ldapSupport then "--enable-ldap" else "--disable-ldap" )
  
positive.code: assert c-aresSupport -> c-ares != null;
  
  stdenv.mkDerivation rec {
    name = "curl-7.45.0";
  
    src = fetchurl {
      url = "http://curl.haxx.se/download/${name}.tar.bz2";
      sha256 = "1slq5c0v9wa8hajgimhkxhvsrd07jmih8sa3gjsl597qp5k4w5b5";
    };
  
    # Zlib and OpenSSL must be propagated because `libcurl.la' contains
    # "-lz -lssl", which aren't necessary direct build inputs of
    # applications that use Curl.
    propagatedBuildInputs = with stdenv.lib;
      optional idnSupport libidn ++
      optional ldapSupport openldap ++
      optional zlibSupport zlib ++
  
negative.code: { stdenv, fetchurl, libnghttp2, pkgconfig, perl
  , idnSupport ? false, libidn ? null
  , ldapSupport ? false, openldap ? null
  , zlibSupport ? false, zlib ? null
  