anchor.diff:      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;
  
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: , http2Support ? true, nghttp2
  , ldapSupport ? true, openldap
  , libxml2Support ? true, libxml2
  , brotliSupport ? true, brotli ? null
  , luaSupport ? false, lua5
  }:
  
  