{
  a.x = 1;
  b.y = 2;
  a.z = 3;
}

Running "Pack all 'a' bindings to nested set" yields:

{
  a = { x = 1; z = 3; };
}

Notice that b.y = 2 was removed.

Version: /nix/store/31ns7kqnsw90p8knh44sjn9gqibjs4bi-nixd-2.9.1