* Some syntactic sugar for attribute sets: allow {x.y.z = ...;} as a

shorthand for {x = {y = {z = ...;};};}.  This is especially useful
  for NixOS configuration files, e.g.

    {
      services = {
        sshd = {
          enable = true;
          port = 2022;
        };
      };
    }

  can now be written as

    {
      services.sshd.enable = true;
      services.sshd.port = 2022;
    }

  However, it is currently not permitted to write
  
    {
      services.sshd = {enable = true;};
      services.sshd.port = 2022;
    }

  as this is considered a duplicate definition of `services.sshd'.

tests/lang/parse-fail-dup-attrs-4.nix

@@ -0,0 +1,4 @@
+{
+  services.ssh.port = 22;
+  services.ssh.port = 23;
+}