anchor.diff:    # `fetchurl' downloads a file from the network.
     fetchurl = makeOverridable (import ../build-support/fetchurl) {
       inherit lib stdenvNoCC;
  -    curl = buildPackages.curl.override rec {
  +    curl = buildPackages.curl.override (old: rec {
         # break dependency cycles
         fetchurl = stdenv.fetchurlBoot;
         zlib = buildPackages.zlib.override { fetchurl = stdenv.fetchurlBoot; };
  
positive.code:       };
        # On darwin, libkrb5 needs bootstrap_cmds which would require
        # converting many packages to fetchurl_boot to avoid evaluation cycles.
        gssSupport = !stdenv.isDarwin && !stdenv.hostPlatform.isWindows;
        libkrb5 = buildPackages.libkrb5.override {
          fetchurl = stdenv.fetchurlBoot;
          inherit pkgconfig perl openssl;
  
negative.code:         c-ares = buildPackages.c-ares.override { fetchurl = stdenv.fetchurlBoot; };
          libev = buildPackages.libev.override { fetchurl = stdenv.fetchurlBoot; };
        };
      });
    };
  
    fetchRepoProject = callPackage ../build-support/fetchrepoproject { };
  