ansible_role_package/tasks/pkgs/zsh.yml

# vim: set filetype=yaml.ansible :
---
- name: append to pkgs
  ansible.builtin.set_fact:
    syspkgs: "{{ syspkgs + [ 'zsh' ] }}"
  when: ansible_os_family != 'Darwin'

- debug:
    msg: "macOS already has zsh, skipping"
  when: ansible_os_family == 'Darwin'