Cannot switch to new configuration (using specialisations)

[RedstoneTrail]

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

run nh os switch --ask ./nixos or nh os switch --ask ./nixos --specialisation hybrid-graphics (my nixos configuration is flake based and in the folder nixos)
output is

> Building NixOS configuration
warning: Git tree '/home/redstonetrail/.dotfiles' is dirty
Finished at 17:01:37 after 16s
Error:
   0: Target profile path does not exist: /tmp/nh-osZzkS34/result/specialisation/hybrid-graphics


Location:
   src/nixos.rs:224

I have a file in /etc/specialisation with the current generation's name, as per the readme.
using a while loop and tree, I have found that the quoted path does exist when the command is running.

running nh os switch --ask ./nixos -S does work, but this of course doesnt apply the specialisation

I am quite sure its not user error, but I am new to this tool.

Installation Method

Flakes (nix profile add) / Channels (nix-env from master branch or from a release)

Installation Method (Other)

Specifically nixos-25.11 in a flake

NH Version

4.2.0

System Information

• system: "x86_64-linux"
• host os: Linux 6.18.6, NixOS, 25.11 (Xantusia), 25.11.20260120.3ceaaa8
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.31.2
• nixpkgs: /nix/store/x2r24fmnvsmcb8sz2fqszbnp72v14hs2-source

[faukah]

Does the file /etc/specialisation contain a newline? I just checked and we do not do any string trimming, that could be the cause of the problem.

[RedstoneTrail]

I found that there was a newline, but after editing my configuration and rebuilding with nixos-rebuild, there is no longer a newline. This hasn't fixed it though, the error message is the same.

(as a note not included in the original post, running with -S does allow building and applying the config, but only the default specialisation)

[faukah]

Before I spend too much time trying to debug and fix this: are you sure it does not contain a newline now? Many editors automatically add one when saving; it could've happened when running wq or something similar.

If this is not the case, I'll try to find the underlying root cause.

[RedstoneTrail]

this is the snippet from my config

    environment.etc = {
      "specialisation".text = if (config.specialisation != { }) then "default" else "hybrid-graphics";
    };

its not whats in the readme verbatim because i was already using a file like this for this state to set arguments in a makefile, but this should be fine, right?

[faukah]

this is the snippet from my config

    environment.etc = {
      "specialisation".text = if (config.specialisation != { }) then "default" else "hybrid-graphics";
    };

its not whats in the readme verbatim because i was already using a file like this for this state to set arguments in a makefile, but this should be fine, right?

yup, that checks out:

No whitespace, so that isn't the problem. I'll try to debug this.