Ansible not evaluating parameters correctly

[Petar Petkov]

Lets suppose we have the following code sample:

- name: Bug report
  hosts: localhost
  gather_facts: no
  connection: local
  vars:
    foo: no
    bar: "{{ foo }}"
  tasks:
    - debug: msg='This should not be skipped!'
      when: not bar

Seeing the code one would expect that the message "This should not be skipped" is displayed when the code is executed. In reality, however, the code gets skipped because the bar parameter is not correctly resolved to its value no. Rewriting the when clause to look like this:

when: not {{ bar }}

seems to fix the problem. 

Also it seems that this problem is only caused when the not operator is used, because if I use the following code sample:

- name: Bug report

  hosts: localhost

  gather_facts: no

  connection: local

  vars:

    foo: yes

    bar: "{{ foo }}"

  tasks:

    - debug: msg='This should not be skipped!'

      when: bar

everything seems to work as expected.

So is this a bug (perhaps a known issue) or am I doing something wrong?

[Matt Martz]

This is mostly due to how ansible casts values when dereferencing.

It is always safest to use the |bool filter when evaluating a variable that you think should be a boolean.

Such as:

when: not bar|bool

Otherwise, in your example it is evaluating the string value "no" instead of a falsely YAML no value.  And a non-zero length string evaluates as truthy.

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Matt Martz
@sivel
sivel.net

[Ivaylo Bratoev]

Seems related to:
https://github.com/ansible/ansible/issues/5094 
https://github.com/ansible/ansible/issues/10460

https://groups.google.com/forum/#!searchin/ansible-project/boolean/ansible-project/b-LtXWtsPnE/yf8JVnGEUf4J

https://groups.google.com/forum/#!searchin/ansible-project/boolean/ansible-project/PcVKMT0Mw9Y/gVqt8YdCpVUJ

It seems this is a source of a lot of confusion. Looking at it - it should be a best practice to use the *bool* filter whenever you use *when*. The documentation doesn't do that and this leads to confusion.

I am interested on the opinions of others - can this be fixed in Ansible to work as expected or should casting to *bool* should be a best practice in *when*-s?