Unexpected evaluation of condition in 'when' statement

[Alfredo M]

Hi all,

I'm trying to figure out why the expression "false and (var is undefined)", when 'var' has the value of an undefined variable, returns true. Here it is an example:

- hosts: localhost
  vars:
  g: "{{ z }}"
  is_false_var: false
  tasks:

  - debug: "msg='this must not be shown'"
    when: (is_false_var) and (b is undefined)
    ignore_errors: yes

  - debug: "msg='this must not be shown'"
    when: (is_false_var) and (g is undefined)
    ignore_errors: yes

  - debug: "msg='this must not be shown'"
    when: (is_false_var) and false
    ignore_errors: yes

  - debug: "msg='this must not be shown'"
    when: (is_false_var) and true
    ignore_errors: yes

  - debug: "msg={{ is_false_var and g is undefined }}"
    ignore_errors: yes

That returns:

PLAY [localhost] ***************************************************************

TASK [setup] *******************************************************************
ok: [localhost]

TASK [debug] *******************************************************************
skipping: [localhost]

TASK [debug] *******************************************************************
ok: [localhost] => {
"msg": "this must not be shown"
}

TASK [debug] *******************************************************************
skipping: [localhost]

TASK [debug] *******************************************************************
skipping: [localhost]

TASK [debug] *******************************************************************
fatal: [localhost]: FAILED! => {"failed": true, "msg": "{{ z }}: 'z' is undefined"}
...ignoring

PLAY RECAP *********************************************************************
localhost : ok=3 changed=0 unreachable=0 failed=0

Any ideas or thoughts about the avobe?

Thanks!