anchor.diff:  , svnSupport, subversionClient, perlLibs, smtpPerlLibs
   , perlSupport ? true
   , nlsSupport ? true
  +, osxkeychainSupport ? stdenv.isDarwin
   , guiSupport
   , withManual ? true
   , pythonSupport ? true
  
positive.code:     make -C contrib/subtree
    '' + (lib.optionalString perlSupport ''
      make -C contrib/diff-highlight
    '') + (lib.optionalString stdenv.isDarwin ''
      make -C contrib/credential/osxkeychain
    '') + (lib.optionalString withLibsecret ''
      make -C contrib/credential/libsecret
  
negative.code: , gzip # needed at runtime by gitweb.cgi
  }:
  
  assert osxkeychainSupport -> stdenv.isDarwin;
  assert sendEmailSupport -> perlSupport;
  assert svnSupport -> perlSupport;
  
  