anchor.diff:      # not worth the effort.
       !(isDarwin && (stdenv.buildPlatform != stdenv.hostPlatform))
     ), libkrb5 ? null
  -, c-aresSupport ? false, c-ares ? null
  -, brotliSupport ? false, brotli ? null
  +, http2Support ? true, nghttp2 ? null
  +, idnSupport ? false, libidn2 ? null
  +, ldapSupport ? false, openldap ? null
  +, opensslSupport ? zlibSupport, openssl ? null
  +, pslSupport ? false, libpsl ? null
   , rtmpSupport ? false, rtmpdump ? null
  -, pslSupport ? false, libpsl ? null
  +, scpSupport ? zlibSupport && !stdenv.isSunOS && !stdenv.isCygwin, libssh2 ? null
  +, wolfsslSupport ? false, wolfssl ? null
  +, zlibSupport ? true, zlib ? null
  +, zstdSupport ? false, zstd ? null
   }:
   
   # Note: this package is used for bootstrapping fetchurl, and thus
  
positive.code:   # "-lz -lssl", which aren't necessary direct build inputs of
    # applications that use Curl.
    propagatedBuildInputs = with lib;
      optional http2Support nghttp2 ++
      optional idnSupport libidn2 ++
      optional ldapSupport openldap ++
      optional zlibSupport zlib ++
      optional zstdSupport zstd ++
      optional gsaslSupport gsasl ++
      optional gssSupport libkrb5 ++
      optional c-aresSupport c-ares ++
      optional opensslSupport openssl ++
      optional gnutlsSupport gnutls ++
      optional wolfsslSupport wolfssl ++
      optional scpSupport libssh2 ++
      optional brotliSupport brotli ++
      optional rtmpSupport rtmpdump ++
      optional pslSupport libpsl;
  
    # for the second line see https://curl.haxx.se/mail/tracker-2014-03/0087.html
    preConfigure = ''
  
negative.code: { lib, stdenv, fetchurl, pkg-config, perl
  , brotliSupport ? false, brotli ? null
  , c-aresSupport ? false, c-ares ? null
  , gnutlsSupport ? false, gnutls ? null
  , gsaslSupport ? false, gsasl ? null
  , gssSupport ? with stdenv.hostPlatform; (
      !isWindows &&
  