nixos-rebuild-ng: `build-vm` doesn't respect `--specialisation`

[DerRockWolf]

Nixpkgs version

• Unstable (26.11)

Describe the bug

nixos-rebuild build-vm & nixos-rebuild build-vm-with-bootloader don't respect the --specialisation flag

Steps to reproduce

nixos-rebuild build-vm --flake . --specialisation niri -v
outputs:

debug: nixos_rebuild.process: calling run with args=['nix', '--extra-experimental-features', 'nix-command flakes', 'build', '--print-out-paths', '/etc/nixos/dotfiles/internal#nixosConfigurations."framework".config.system.build.vm', '-v'], kwargs={'stdout': -1}, env=None, append_local_env=None

Expected behaviour

It should build the specialized configuration:

debug: nixos_rebuild.process: calling run with args=['nix', '--extra-experimental-features', 'nix-command flakes', 'build', '--print-out-paths', '/etc/nixos/dotfiles/internal#nixosConfigurations."framework".config.specialisation.niri.configuration.system.build.vm', '-v'], kwargs={'stdout': -1}, env=None, append_local_env=None

So config.specialisation.NAME.configuration.system.build.vm instead of config.system.build.vm

Screenshots

No response

Relevant log output

Additional context

No response

System metadata

Notify maintainers

@thiagokokada

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