nixos-rebuild, nixos-install: add support for --file and --attr flags

[amozeo]

Description of changes

Allows building NixOS and using nixos-rebuild commands with a NixOS configuration located in plain nix file. This is useful for using nixos-rebuild command with a NixOS system configuration located in a nix file that is not a flake or a NixOS configuration module.

if you want to test this feature with your own configuration (if not using flakes), you can use this

{ nixosEval ? import <nixpkgs/nixos/lib/eval-config.nix> }:

nixosEval {
  modules = [( import <path/to/nixosConfiguration.nix> )];
}

NixOS configuration in plain nix file can be created using nixos function in nixpkgs, or importing and calling nixos/lib/eval-config.nix.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • nixos/tests/installer.nix simple
  • nixos/tests/installer.nix switchToFlake
  • nixos/tests/installer.nix switchToByAttr (new test)
  • nixos/tests/installer.nix switchFromByAttrToFlake (new test)
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

maintainer mention: @Profpatsch

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[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review/3032/4235

[AndersonTorres]

Looks very nice!

[tomberek]

Result of nixpkgs-review pr 320462 run on x86_64-linux 1

2 packages blacklisted:

• nixos-install-tools
• tests.nixos-functions.nixos-test

5 packages built:

• nixos-rebuild
• tests.testers.lycheeLinkCheck.network
• tests.testers.nixosTest-example
• tests.testers.runNixOSTest-example
• tests.trivial-builders.references

[tomberek]

Builds, runs, tests as expected.

[infinisil]

This is awesome! I just opened #333788 to take this to the next step, but unfortunately I don't have the time to pull it through, so I'd appreciate if you could help out with that @amozeo 🙏