anchor.diff:  { lib, stdenv, fetchurl, fetchpatch, openssl, zlib, pcre, libxml2, libxslt
  +
   , nixosTests
   , substituteAll, gd, geoip, perl
   , withDebug ? false
  
positive.code:     "--with-debug"
    ] ++ optionals withStream [
      "--with-stream"
      "--with-stream_geoip_module"
      "--with-stream_realip_module"
      "--with-stream_ssl_module"
      "--with-stream_ssl_preread_module"
  
negative.code:     "--with-perl_modules_path=lib/perl5"
    ]
      ++ optional (gd != null) "--with-http_image_filter_module"
      ++ optional (geoip != null) "--with-http_geoip_module"
      ++ optional (withStream && geoip != null) "--with-stream_geoip_module"
      ++ optional (with stdenv.hostPlatform; isLinux || isFreeBSD) "--with-file-aio"
      ++ configureFlags
      ++ map (mod: "--add-module=${mod.src}") modules;
  