[hamandcheese]

What do you mean by auto-upgrade behavior?

If the Django package in nix were upgraded, all packages that use it would be tested.

And you wouldn't get the upgrade automatically, instead you would only get the upgrade when you change the version of Nixpkgs that you are using.

And if you don't like that, then you can use multiple versions of Nixpkgs at the same time. Your old package will stay exactly as it was. This of course cuts both ways, and means you get no security updates for it or any of its transitive dependencies.

Which part of this isn't reproducible or functional? If nixpkgs never changed, it wouldn't be a very good package repository.