assert versionOlder

Sometimes you have to override a specific package with something that's newer than what's available in nixpkgs. Often times – if you're me at least – you'll forget having done that later and will keep the override on a then older version than what's available in nixpkgs. In that case, it can make sense to do the following so nix will fail your build once the package advances enough.

package =
  assert lib.assertMsg (lib.versionOlder pkgs.fosrl-newt.version "1.16.0")
    "nixpkgs now ships fosrl-newt >= 1.16.0 - remove this override";
  pkgs.fosrl-newt.overrideAttrs (old: rec {
    # ...
  });