Ansible: Skipping items in a loop based on item key's value - ansible

Question

I'm fiddling around with loops and conditional skips.
Given the following playbook, everything works fine (mind the commented part, that I will use later on)
playbook.yml:
- name: Play Test
hosts: all
gather_facts: false
vars:
test1_var: "test1_var"
test3_var: "{{ default(omit) }}" # omitted
test4_var: # None
tasks:
- block:
- name: Test some skips in loops
ansible.builtin.debug:
msg: "Text:{{ item.text }}|Variable:{{item.variablez}}"
loop:
- text: "Should be logged"
variablez: "{{ test1_var }}"
- text: "Should be skipped"
#- text: "Should be skipped"
# variablez: "{{ test3_var | default(omit) }}"
- text: "Should be skipped"
variablez: "{{ test4_var }}"
when: item.variablez is defined and item.variablez != None
delegate_to: localhost
Output:
TASK [Test some skips in loops] ******************************************************************************************************************************************************************************************
ok: [mosquitto -> localhost] => (item={'text': 'Should be logged', 'variablez': 'test1_var'}) =>
msg: Text:Should be logged|Variable:test1_var
skipping: [mosquitto] => (item={'text': 'Should be skipped'})
skipping: [mosquitto] => (item={'text': 'Should be skipped', 'variablez': None})
The second item has no key item.variablez so it is skipped.
The third item is skipped because item.variablez is None.
Now when I uncomment the part
- text: "Should be skipped"
variablez: "{{ test3_var | default(omit) }}" # Also "{{ default(omit) }}" leads to the same result
I would expect the item simply to be skipped. Because item.variablez and or test3_var is omitted. But instead the whole task is skipped:
PLAY [Play Test] *********************************************************************************************************************************************************************************************************
TASK [Test some skips in loops] ******************************************************************************************************************************************************************************************
skipping: [mosquitto]
PLAY RECAP ***************************************************************************************************************************************************************************************************************
mosquitto : ok=0 changed=0 unreachable=0 failed=0 skipped=1 rescued=0 ignored=0
Now I try to understand why this is happening. Does anybody know that?

Answer 1

This appears to be due to a loop processing bug in ansible-core<2.14 (the changes in https://github.com/ansible/ansible/pull/56116 make the loop execution more correct in 2.14), but the root cause is an invalid variable definition.
test3_var: "{{ default(omit) }}" # omitted
This is not a valid expression; default() is a filter, so it needs to receive a value. You probably meant this:
test3_var: "{{ omit }}" # omitted
Note that while this will fix the problem with the loop definition not being valid, you will still have a logic problem because omit and None are not the same thing.
omit is a variable holding a special string that can be used as a parameter and is treated by the execution engine as that parameter not being present, but outside of parameter processing it's just a normal string. Since omit != None, your task will run and output the value of omit as part of the message:
ok: [localhost] => (item={'text': 'Should be skipped', 'variablez': '__omit_place_holder__180f8c0850ccb5c85940241213b4e1590ec6c326'}) => {
"msg": "Text:Should be skipped|Variable:__omit_place_holder__180f8c0850ccb5c85940241213b4e1590ec6c326"
If you want to use omit as a flag you need to check for it explicitly:
- name: Play Test
hosts: all
gather_facts: false
vars:
test1_var: "test1_var"
test3_var: "{{ omit }}" # omitted
test4_var: # None
tasks:
- name: Test some skips in loops
ansible.builtin.debug:
msg: "Text:{{ item.text }}|Variable:{{item.variablez}}"
loop:
- text: "Should be logged"
variablez: "{{ test1_var }}"
- text: "Should be skipped"
- text: "Should be skipped"
variablez: "{{ test3_var | default(omit) }}"
- text: "Should be skipped"
variablez: "{{ test4_var }}"
when:
- item.variablez is defined
- item.variablez not in (None, omit)