Can't build image from attr

[mewoocat]

I have confirmed that this is a bug related to nh

• This is a bug, and not an user error or a support request. I understand that my issue will be closed if it is not a bug in NH.
• I have checked the issues tab and confirmed that my issue has not yet been reported. I understand that my issue will be closed if it is a duplicate.

Description

I'm using a non flake tack based setup and I'm having a problem with building an iso image for it.

When I run nh os build-image --image-variant iso -f ~/NixOS obsidian, it outputs

             error: attribute 'config' missing
             at «string»:7:22:
                  6| in
                  7|   builtins.attrNames config.config.system.build.images
                   |                      ^
                  8|

where ~/NixOS/default.nix is https://github.com/mewoocat/NixOS/blob/506fe7805186febb2f0a2826f6b81fb166319452/default.nix#L52-L53

Since ~/NixOS/.default.nix's obsidian attribute outputs a eval-config.nix nixos system using ~NixOS/hosts/obsidian/configuration.nix, that should qualify as a valid installer right?

I normally use nh os switch -f ~/NixOS obsidian to rebuild which works fine.

Installation Method

Stable Release (nixpkgs, pkgs.nh from nixos-unstable or nixos-yy-mm)

Installation Method (Other)

No response

NH Version

nh 4.4.2

System Information

system:

• host os: NixOS-26.05
• multi-user: no
• sandbox: no
• version 26.05
• nixpkgs: 70cc4559b10a6062b05ff1af17e0add065ccaed9