anchor.diff:  , runCommand, pkgconfig, meson, ninja, makeWrapper
   # build+runtime deps.
   , knot-dns, luajitPackages, libuv, gnutls, lmdb, systemd, dns-root-data
  +, nghttp2
   # test-only deps.
   , cmocka, which, cacert
   , extraFeatures ? false /* catch-all if defaults aren't enough */
  
positive.code:   '';
  
    doInstallCheck = with stdenv; hostPlatform == buildPlatform;
    installCheckInputs = [ cmocka which cacert lua.cqueues lua.basexx ];
    installCheckPhase = ''
      meson test --print-errorlogs
    '';
  
negative.code:   # http://knot-resolver.readthedocs.io/en/latest/build.html#requirements
    buildInputs = [ knot-dns lua.lua libuv gnutls lmdb ]
      ++ optional stdenv.isLinux systemd # passing sockets, sd_notify
      ++ [ nghttp2 ]
      ## optional dependencies; TODO: libedit, dnstap
      ;
  
  