Ansible non-empty string conditional variants

is_not_empty.yml

---

# test scenario for task when conditional test for non-empty string
# example command line: ansible-playbook -i "localhost," is_not_empty.yml 

- hosts: all
  gather_facts: false
  tasks:
    # at this point foo is not defined, so we expect task to skip
    
    # skips as expected
    - name: Display value of foo with condition foo is defined and foo != ''
      debug: var=foo
      when: foo is defined and foo != ''
    # skips as expected
    - name: Display value of foo with condition foo | default(false)
      debug: var=foo
      when: foo | default(false)
    # will return 'foo is not defined' error
    - name: Display value of foo with condition foo
      debug: var=foo
      ignore_errors: true
      when: foo
    # will return 'foo is not defined' error
    - name: Display value of foo with condition "{ {foo} }"
      debug: var=foo
      ignore_errors: true
      when: "{{foo}}"

    - set_fact: foo=''

    # when foo contains empty string we expect task to be skipped

    # skips as expected
    - name: Display value of foo with condition foo is defined and foo != ''
      debug: var=foo
      when: foo is defined and foo != ''
    # skips as expected
    - name: Display value of foo with condition foo | default(false)
      debug: var=foo
      when: foo | default(false)
    # skips as expected
    - name: Display value of foo with condition foo
      debug: var=foo
      ignore_errors: true
      when: foo
    # skips as expected
    - name: Display value of foo with condition "{ {foo} }"
      debug: var=foo
      ignore_errors: true
      when: "{{foo}}"

    - set_fact: foo='bar'

    # when foo contains a string value we expect task to run

    # runs as expected
    - name: Display value of foo with condition foo is defined and foo != ''
      debug: var=foo
      when: foo is defined and foo != ''
    # runs as expected
    - name: Display value of foo with condition foo | default(false)
      debug: var=foo
      when: foo | default(false)
    # curiously this when condition evaluates foo down to bar, then returns a 'bar is not defined' error
    - name: Display value of foo with condition foo
      debug: var=foo
      ignore_errors: true
      when: foo
    # curiously this when condition evaluates foo down to bar, then returns a 'bar is not defined' error
    - name: Display value of foo with condition "{ {foo} }"
      debug: var=foo
      ignore_errors: true
      when: "{{foo}}"