Impure evaluation (--impure) not propagated to inner home-manager activation due to locked flake path

[HariAmoor-professional]

Hi @srid,

I'm encountering an issue where running nix run .# --impure -- --impure (to activate my home-manager config impurely) doesn't work as expected. The activation script uses a locked, store-path flake (e.g., /nix/store/...#hariamoor), which enforces pure evaluation mode and blocks impure builtins like builtins.fetchurl without a hash, even with --impure passed.

Steps to Reproduce:

1. Set up a flake with nixos-unified (e.g., basic home-manager config using autoWire).
2. Add an impure fetch in the config, like:

   let wallpaper = builtins.fetchurl "https://example.com/image.jpg";

3. Run nix run .# --impure -- --impure.
4. Observe the error: "in pure evaluation mode, 'fetchurl' requires a 'sha256' argument".

Expected Behavior:

The --impure flag should propagate to the inner home-manager switch call, allowing impure evaluation similar to running home-manager switch --flake .#config --impure directly.

Actual Behavior:

The inner call uses a locked store path, which ignores --impure and enforces purity.

Workaround:

Directly running home-manager switch --flake .#config --impure works, but bypasses the unified activation.

This seems like a limitation in how the activation script handles locked flakes. Could you add support for optional impure activations, perhaps via a flag to use the original flake path (.) instead of the locked one when --impure is detected?

Thanks for looking into this!

Environment:

• NixOS version: 24.05 (or unstable, as in my flake)
• nixos-unified: latest from github:srid/nixos-unified
• home-manager: following nixpkgs-unstable

You can find a repro Flake with my NixOS config (hosted on Gitea!)

[niksingh710]

Both this issue and the discussion could benefit from changes to the activation script.

[HariAmoor-professional]

@niksingh710 I think what you're talking about is out-of-scope for this issue. I just want home-manager to switch on nix run .# from my nixos-unified repo.

I'm not sure if what I'm asking for somehow makes your thing trivial though.