specialisations break the system argument

[bbjubjub2494]

Describe the bug
A clear and concise description of what the bug is.
When the NixOS specialisations feature is used and any NixOS module evaluates the system attribute in its arguments, an EvalError occurs when instantating.

Introduced by 684804e

relevant nixpkgs snippet

To Reproduce
Steps to reproduce the behavior:

1. Check Minimal Working Example
2. See error

Expected behavior
The configuration should build cleanly.

Additional context

[nrdxp]

I'm unable to reproduce this after checking out your mentioned branch and running nix flake check. Also tried rebuild iso. What exactly is the error your getting, or what command are you running to produce the error on this branch?

edit Nevermind, I got the error. Working now to find best solution. Possibly reverting the commit might be the best thing to do.

[nrdxp]

I can't remember what my initial impetus was for adding this to extraArgs. I am assuming it was to access the value of system, which should also be available via nixpkgs.system, which apparently, I did't know at the time. Thus, it seems that the best solution is simply to remove the extraArgs attribute all together and if you need to reference your current system in your config do something like so:

{ config, ... }:
{
    lib.whatIsMySystem = config.nixpkgs.system; 
}

I'll send in a pull to close this in a bit, unless you have any objections?

[bbjubjub2494]

I would say pkgs.system is slightly more future-proof since it comes somewhat directly from flake.nix rather than through some NixOS snippets that set the default value that we don't control. otherwise. It's also shorter.

[nrdxp]

good point I'll rebase the pr