Tasks inside a block that use a loop are not skipped even if the block's when condition evaluates to false

[lpugoy]

SUMMARY

Tasks inside a block that use a loop are not skipped even if the block's when condition evaluates to false. Tasks that don't use a loop are skipped.

ISSUE TYPE

• Bug Report

COMPONENT NAME

Loops

ANSIBLE VERSION

ansible 2.9.1
  config file = /<scrubbed>/src/github.com/<scrubbed>/ansible.cfg
  configured module search path = ['/<scrubbed>/src/github.com/<scrubbed>/library']
  ansible python module location = /<scrubbed>/.virtualenvs/ansible/lib/python3.7/site-packages/ansible
  executable location = /<scrubbed>/.virtualenvs/ansible/bin/ansible
  python version = 3.7.5 (default, Nov  1 2019, 02:16:32) [Clang 11.0.0 (clang-1100.0.33.8)]

CONFIGURATION

DEFAULT_MODULE_PATH(/<scrubbed>/src/github.com/<scrubbed>/ansible.cfg) = ['/<scrubbed>/src/github.com/<scrubbed>/library']
DEFAULT_ROLES_PATH(/<scrubbed>/src/github.com/<scrubbed>/ansible.cfg) = ['/<scrubbed>/src/github.com/<scrubbed>']
INTERPRETER_PYTHON(/<scrubbed>/src/github.com/<scrubbed>/ansible.cfg) = /usr/bin/python3

OS / ENVIRONMENT

OS version: macOS Mojave 10.14.6

STEPS TO REPRODUCE

- hosts: all
  gather_facts: no
  tasks:
  - name: Initialize variable
    set_fact:
      foo:

  - name: Print result of "foo is not none"
    debug:
      msg: "{{ foo is not none }}"

  - block:
    - name: This task is skipped
      debug:
        msg: I'm skipped :)

    - name: This task that uses loop is not skipped
      debug:
        msg: I'm not skipped :(
      loop: "{{ foo | dict2items }}"
    when: foo is not none

EXPECTED RESULTS

$ ansible-playbook -i localhost, /tmp/loop_bug.yml

PLAY [all] *************************************************************************************************************************************************************************************************

TASK [Initialize variable] *********************************************************************************************************************************************************************************
ok: [localhost]

TASK [Print result of "foo is not none"] *******************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": false
}

TASK [This task is skipped] ********************************************************************************************************************************************************************************
skipping: [localhost]

TASK [This task that uses loop is not skipped] *************************************************************************************************************************************************************
skipping: [localhost]

PLAY RECAP *************************************************************************************************************************************************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0    skipped=2    rescued=0    ignored=0

ACTUAL RESULTS

$ ansible-playbook -i localhost, /tmp/loop_bug.yml

PLAY [all] *************************************************************************************************************************************************************************************************

TASK [Initialize variable] *********************************************************************************************************************************************************************************
ok: [localhost]

TASK [Print result of "foo is not none"] *******************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": false
}

TASK [This task is skipped] ********************************************************************************************************************************************************************************
skipping: [localhost]

TASK [This task that uses loop is not skipped] *************************************************************************************************************************************************************
fatal: [localhost]: FAILED! => {"msg": "dict2items requires a dictionary, got <class 'NoneType'> instead."}

PLAY RECAP *************************************************************************************************************************************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=1    skipped=1    rescued=0    ignored=0

[ansibot]

Files identified in the description:

• test/integration/targets/loops/aliases

If these files are inaccurate, please update the component name section of the description or use the !component bot command.

click here for bot help

[Akasurde]

!component =lib/ansible/executor/task_executor.py

[ansibot]

Files identified in the description:

• lib/ansible/executor/task_executor.py

If these files are inaccurate, please update the component name section of the description or use the !component bot command.

click here for bot help

[sivel]

This is expected. A when statement on a block does not prevent the block from being evaluated, instead, think of any keyword that is applied to a block, being merged down onto the underlying tasks.

So this:

  - block:
    - name: This task is skipped
      debug:
        msg: I'm skipped :)

    - name: This task that uses loop is not skipped
      debug:
        msg: I'm not skipped :(
      loop: "{{ foo | dict2items }}"
    when: foo is not none

Is equivalent to:

  - name: This task is skipped
    debug:
      msg: I'm skipped :)
    when: foo is not none

  - name: This task that uses loop is not skipped
    debug:
      msg: I'm not skipped :(
    loop: "{{ foo | dict2items }}"
    when: foo is not none

Per the documentation at https://docs.ansible.com/ansible/latest/user_guide/playbooks_conditionals.html#loops-and-conditionals :

Combining when with loops (see Loops), be aware that the when statement is processed separately for each item. This is by design.

The meaning of that, is that the when statement is evaluated for each iteration of the loop, and not before the loop. As a result, your loop must always evaluate as an iterable, regardless of the when statement.

As such, you would need to change your loop to read something like the following:

    loop: "{{ foo | default({}) | dict2items }}"

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