* 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'.

src/libexpr/nixexpr.cc

@@ -19,7 +19,7 @@ string showPos(ATerm pos)
     if (matchNoPos(pos)) return "undefined position";
     if (!matchPos(pos, path, line, column))
         throw badTerm("position expected", pos);
-    return (format("`%1%', line %2%") % aterm2String(path) % line).str();
+    return (format("`%1%:%2%:%3%'") % aterm2String(path) % line % column).str();
 }