Ansible Unable to assign variable the value to another variable - variables

Question

If the user does not pass dest_path parameter or if dest_path is EMPTY i.e contains only whitespaces then dest_path should be the same as source_file value.
Below is my playbook:
---
- name: "Play 1"
hosts: localhost
any_errors_fatal: false
gather_facts: false
tasks:
- set_fact:
dest_path: "{{ dest_path | default(source_file) }}"
- set_fact:
dest_path: "{{ source_file }}"
when: dest_path | length == 0
- debug:
msg: "DESTINATION PATH IS: {{ dest_path }} and the SOURCE PATH is: {{ source_file }}"
This is how you run this playbook:
ansible-playbook -i /web/playbooks/allmwhosts.hosts /web/playbooks/test.yml -e '{ source_file: /web/bea_apps/CURRENT }' -e dest_path=
In the above example when the user does not specify any value for dest_path I m expecting dest_path should be source_file i.e /web/bea_apps/CURRENT
However, as you can see in the output below that is not the case:
Output:
PLAY [Play 1] *******************
TASK [set_fact] **************************************************************************************
ok: [localhost]
TASK [set_fact] **************************************************************************************
ok: [localhost]
TASK [debug] *****************************************************************************************
ok: [localhost] => {
"msg": "DESTINATION PATH IS: and the SOURCE PATH is: /web/bea_apps/CURRENT"
}
PLAY RECAP *******************************************************************************************
localhost : ok=3 changed=0 unreachable=0 failed=0
Can you please suggest?

Answer 1

The extra variable that you pass as parameter is overriding the variable in set_fact variable dest_path. Below is the working code. In set_fact instead of dest_path I replaced with path.
---
- name: "Play 1"
hosts: localhost
any_errors_fatal: false
gather_facts: false
tasks:
- set_fact:
path: "{{ source_file }}"
when: (dest_path is not defined) or (dest_path | length == 0)
- set_fact:
path: "{{ dest_path }}"
when: (dest_path is defined) or (dest_path | length != 0)
- debug:
msg: "DESTINATION PATH IS: {{ path }} and the SOURCE PATH is: {{ source_file }}"