ansible/test/integration/targets/set_fact/incremental.yml

- name: test set_fact incremental https://github.com/ansible/ansible/issues/38271
  hosts: testhost
  gather_facts: no
  tasks:
    - name: Generate inline loop for set_fact
      set_fact:
        dig_list: "{{ dig_list + [ item ] }}"
      loop:
        - two
        - three
        - four
      vars:
        dig_list:
            - one

    - name: verify cumulative set fact worked
      assert:
        that:
           - dig_list == ['one', 'two', 'three', 'four']

    - name: Generate inline loop for set_fact (FQCN)
      ansible.builtin.set_fact:
        dig_list_fqcn: "{{ dig_list_fqcn + [ item ] }}"
      loop:
        - two
        - three
        - four
      vars:
        dig_list_fqcn:
            - one

    - name: verify cumulative set fact worked (FQCN)
      assert:
        that:
           - dig_list_fqcn == ['one', 'two', 'three', 'four']