Use different nixpkgs versions for nix-script and what it builds

[Nadrieril]

There are two ways of installing nix-script: I can choose to use either your pinned nixpkgs version, or specify my own. The problem I have is that I have a script that requires nixpkgs-unstable to build, but nix-script cannot be built with that because it requires hnix < 14. So either way poses a problem.
However it's not a priori necessary to use the same version of nixpkgs to build nix-script and to run nix-script. So would it be possible to pin nixpkgs only for the purpose of finding script dependencies, while letting nix-script be built with its own version?

[Nadrieril]

I see that you've run into this problem already: 78b063f

[BrianHicks]

yeah, I'm open to PRs that update the version bounds so you don't have to resort to jailbreak hacks!

[Nadrieril]

That shouldn't be required though, I'm proposing a different solution that doesn't require updating nix-script to support all imaginable nixpkgs versions

[Nadrieril]

EDIT: I figured it out. What I'd like is a way to change the nixpkgs version passed to this line without that version being used to build nix-script. But I don't understand flakes enough to know how to make it work.

[GTrunSec]

I did a flake example here
https://github.com/GTrunSec/Coding-Dev-Env-With-NixFlake/tree/main/nix-script

[BrianHicks]

mm, I misunderstood you before then @Nadrieril; sorry about that! Basically: I think the mechanism that we use for this feels pretty hacky currently and could improve a lot. For example, it's not possible to source a nixpkgs from niv with the current setup. Do you have any ideas on how to solve the problem? (Or, could you say more about the solution you briefly described at the top here?)

[Nadrieril]

The thing I have in mind is very close to what you do today. I propose that you simply remove this line, so that nix-script uses whatever $NIX_PATH is found at runtime to build its scripts. I think this is what users expect even.
Then if a user wants to pin a specific nixpkgs version, they can simply wrap nix-script using wrapProgram to pin $NIX_PATH. Maybe this can also be available as an option when building/importing nix-script, but I don't understand flakes very well.
The difference with the current behavior (or at least with what happened before #22 broke "controlling nixpkgs version") is that with the new thing, pinning a nixpkgs version can no longer break the building of nix-script, since nix-script would always be built with its own pinned dependencies.
Am I making sense?

[BrianHicks]

Your analysis and solution sound fine to me! I don't think this will break anything about flakes. Wanna do it and send a PR?

[GTrunSec]

The difference with the current behavior (or at least with what happened before #22 broke "controlling nixpkgs version") is that with the new thing, pinning a nixpkgs version can no longer

you can try the example as following:

• with nix-shell

let
  pkgs = import
    (builtins.fetchTarball {
      url = "https://github.com/NixOS/nixpkgs/tarball/36a05ec28e46d610aab8d05e56e4442c5866b8c7";
      sha256 = "0g95fbj4h1rsdyd81vfl5cwv9p7hfvmbgfhvp5k1sni73zccikl6";
    })
    {
      overlays = [ nix_script.overlay ];
    };
  nix_script = (builtins.getFlake "github:BrianHicks/nix-script");
in
pkgs.mkShell
{
  buildInputs = [ pkgs.nix-script ];
}

Also, we need to update the readme as well.