bool filter wrongly treats nonempty strings/sequences/dicts as 'false'

[pjnagel]

ISSUE TYPE

• Bug Report

COMPONENT NAME

builtin filters

ANSIBLE VERSION

ansible 2.3.1.0
  config file = /home/pieter.nagel/setup/lautus_ansible/ansible.cfg
  configured module search path = Default w/o overrides
  python version = 3.5.2 (default, Nov 17 2016, 17:05:23) [GCC 5.4.0 20160609]

CONFIGURATION

Nothing relevant

OS / ENVIRONMENT

Running Ansible on Ubuntu 16.04.2 LTS.

SUMMARY

The bool filter does not reliably cast all true values to 'true'. In particular, nonempty strings, and nonempty sequences, and nonempty dictionaries, are all cast to 'false'.

STEPS TO REPRODUCE

---
- name: debug
  hosts: localhost
  vars:
    v1: stuff
    v2: true
    v3:
      - a
      - b
      - c
    v4:
      a: 1
      b: 2
  tasks:

  - debug: msg='String is true'
    when: 'v1 | bool'

  - debug: msg='True is true'
    when: 'v2 | bool'

  - debug: msg='Nonempty list is true'
    when: 'v3 | bool'

  - debug: msg='Nonempty dict is true'
    when: 'v4 | bool'

EXPECTED RESULTS

I expect to see all four debug statements print their messages.

ACTUAL RESULTS

The only debug statement that is not skipped is 'True is true'.

 [WARNING]: Host file not found: /etc/ansible/hosts

 [WARNING]: provided hosts list is empty, only localhost is available


PLAY [debug] **********************************************************************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ************************************************************************************************************************************************************************************************************************************************************
ok: [localhost]

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

TASK [debug] **********************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "True is true"
}

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

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

PLAY RECAP ************************************************************************************************************************************************************************************************************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0   

[jctanner]

@pjnagel The implementation for this filter is fairly simple ...

https://github.com/ansible/ansible/blob/devel/lib/ansible/plugins/filter/core.py#L117-L125

def to_bool(a):
    ''' return a bool for the arg '''
    if a is None or isinstance(a, bool):
        return a
    if isinstance(a, string_types):
        a = a.lower()
    if a in ('yes', 'on', '1', 'true', 1):
        return True
return False

I think what are you asking for is ...

def to_bool(a):
    ''' return a bool for the arg '''
    if a is None or isinstance(a, bool):
        return a
    if isinstance(a, string_types):
        a = a.lower()
    if a in ('yes', 'on', '1', 'true', 1):
        return True

    # true for anything else that is not length 0
    if len(a) > 0:
        return True
    
return False

Is that correct?

needs_info

[sivel]

There is another pull request to add a "python" truthiness evaluation branch to to_bool that would likely resolve this issue:

#22021

I fear that any change made to the bool filter at this point to accept an empty string as false, would be a backwards incompatible change that could cause problems for existing playbooks.

[bcoca]

The bool filter is not pythonic, it is not meant to be, closing this in favor of the feature request as this currently works as expected.

[sivel]

fwiw, as a work around, to get this behavior currently, you can do:

some_var|default(False, boolean=True)|bool

The boolean argument to default tells jinja2 to do a python truthiness check on the var. So default would see "" as falsey and substitute the boolean False.