nixos-config/modules/system/shell/default.nix

{ pkgs,  ... }:
{
  programs.zsh.enable = true;
  programs.zsh.enableCompletion = true;
  programs.zsh.syntaxHighlighting.enable = true;
  programs.zsh.autosuggestions.enable = true;
  programs.zsh.autosuggestions.async = true;
  programs.zsh.ohMyZsh.enable = true;
  programs.zsh.ohMyZsh.theme = "agnoster";
  users.defaultUserShell = pkgs.zsh;
}