Nixpkgs: nix-channel --help not working

[hloeffler]

Describe the bug
nix-channel --help
shows
sh: nroff: command not found

To Reproduce
Steps to reproduce the behavior:

1. nix-channel --help

Expected behavior
output

Additional context
nix-channel --help =>sh: nroff: command not found

man man =>man: no manual entry for 'man'

nixos-option documentation.man.enable => Value:true

this is working:

nix run nixpkgs.groff -c nix-channel --help

Notify maintainers

Metadata

• system: "x86_64-linux"
• host os: Linux 5.4.58, NixOS, 20.03.2835.ebf59916232 (Markhor)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.6
• channels(root): "nixos-20.03.2835.ebf59916232, nixos-hardware"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:

[siraben]

Do you have man-pages installed on your system?

[hloeffler]

@siraben
via environment.systemPackages => no

now i have, and it does not change it.

[hloeffler]

maybe its my man?

is this the right one?

BusyBox v1.31.1 () multi-call binary.

i don't know where i got busybox from, i don't installed it.

[hloeffler]

my fault,
i tried do build a package, and after removing it and running: nix-env -q its all good again :/