Failure on nixos-option completion

[toothbrush]

Description

I'm running into an issue where nixos-option isn't able to complete. I think the failure is inside _nix_eval_stdin, but i'm not sure why. It's returning empty from inside _nix_attr_paths. The error shown is:

$ nixos-option
Completing Eval failed, can't complete (an URL might not be cached):
 
Trace output left in /tmp/zsh28661nixos-option2 (up-history to view)

I have a fair bit of configuration in my .zshrc, from before when i used to run Arch Linux -- so perhaps this is messing with me, but i'm not sure how to debug -- apologies! However, when I completely remove my own Zsh config, things still seem to break.

I've set programs.zsh.enable = true; in my configuration.nix, and many of the completions seem fine, e.g. nixos-option --<TAB> expands to nixos-option --all.

Reproduction steps

Set programs.zsh.enable = true; in configuration.nix, restart session, open terminal and type nixos-option <TAB>.

System

• nix-zsh-completions version: nix-zsh-completions-0.4.4
• ZSH version: 5.8
• NIX_PATH: nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos:nixos-config=/etc/nixos/configuration.nix:/nix/var/nix/profiles/per-user/root/channels
• system: "x86_64-linux"
• host os: Linux 5.8.6, NixOS, 21.03.git.8418716f7b9 (Okapi)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.7
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Completion trace

With no ~/.zshrc at all: https://gist.github.com/toothbrush/17426406b47b71934358019eda5ad171
With my usual ~/.zshrc: https://gist.github.com/toothbrush/4f32d5bcd63fb6e238567f1b3a3f5e3c

[Freed-Wu]

I can reproduce this bug:

$ nixos-option <TAB>
Eval failed, can't complete (an URL might not be cached):