anchor.diff:  , http2Support ? true, nghttp2
   , ldapSupport ? true, openldap
   , libxml2Support ? true, libxml2
  +, brotliSupport ? true, brotli ? null
   , luaSupport ? false, lua5
   }:
   
  
positive.code:   setOutputFlags = false; # it would move $out/modules, etc.
  
    buildInputs = [perl] ++
      optional sslSupport openssl ++
      optional ldapSupport openldap ++    # there is no --with-ldap flag
      optional libxml2Support libxml2 ++
  
negative.code:     optionalString = stdenv.lib.optionalString;
  in
  
  assert brotliSupport -> brotli != null;
  assert sslSupport -> aprutil.sslSupport && openssl != null;
  assert ldapSupport -> aprutil.ldapSupport && openldap != null;
  assert http2Support -> nghttp2 != null;
  