Fails to run in pure evaluation mode

[soispha]

How to reproduce

1. Add nix.pure-eval = true to your nixos-config (or add pure-eval = true in nix.conf).
2. Every try to run nixpkgs-review will now fail, as access to the nixpath (<nixpkgs>) is forbidden.

Possible fixes

• Either add --impure to every nix invocation that tries to access <nixpkgs> or
• Remove the need to import <nixpkgs> in the first place.

Implementing the second idea would probably necessitate adding a hash backed builtins.fetchTarball call, or something like it, to get access to nixpkgs.

[Mic92]

I don't think you can have this set globally and still expects all tools to work properly. This should be only set on a cli level.

[Mic92]

We are already passing --impure to nix and use --nix-path instead of '<nixpkgs>'.

[Mic92]

I don't want to also add workarounds for this configuration. This would also break normal nix-shell usage and co. Don't do it or live with the consequences.