ansible-core 2.14 and determining if top level variables exist in source

[Chris Nokes]

Hi,

I just opened https://github.com/ansible/ansible/issues/79874 and Matt explained that 2.14 change is working as designed and closed the issue.

Matt put a link in the issue describing variable lazy eval and how undefined variables now work:

https://docs.ansible.com/ansible-core/2.14/porting_guides/porting_guide_core_2.14.html#playbook

I believe I'm tracking those changes, but I'm still lost on how my use case can be implemented.  My specific use case was a task's when clause determining to execute based on a top level variable being "authored".  If the author made a mistake in the nested elements, then an exception is desired.  How can this use case be implemented in 2.14?

Thanks,

Chris

[Felix Fontein]

Hi,

> I just opened https://github.com/ansible/ansible/issues/79874 and
> Matt explained that 2.14 change is working as designed and closed the
> issue.
>
> Matt put a link in the issue describing variable lazy eval and how
> undefined variables now work:
> https://docs.ansible.com/ansible-core/2.14/porting_guides/porting_guide_core_2.14.html#playbook

if someone is interested, the implementation of that change happened in
https://github.com/ansible/ansible/pull/56116

> I believe I'm tracking those changes, but I'm still lost on how my
> use case can be implemented. My specific use case was a task's when
> clause determining to execute based on a top level variable being
> "authored". If the author made a mistake in the nested elements,
> then an exception is desired. How can this use case be implemented
> in 2.14?

I'm not sure it can actually be implemented anymore, at least for
something that works in the form of `nested is my_undefined_test`.
Maybe it is still possible to do something like `"nested" is
my_undefined_test`, where `my_undefined_test` is a custom test plugin
which checks whether a global object of that name seems to exist. But
that depends on how Jinja2 internally works, which I know too little
about.

Best,
Felix

[flowerysong]

You can use the varnames lookup to determine whether a top-level variable exists:

 

- name: Run when foo exists

  debug:

  when: query('varnames', '^foo$')

If you want to do a preflight check that the variable is defined properly, you can do something like this:

- assert:

    that: foo is defined

  when: query('varnames', '^foo$')

Then you can continue using `when: foo is defined` on your actual task(s), since you have asserted that the variable is either fully undefined or fully defined.

[Rowe, Walter P. (Fed)]

How do these differ?

  when: query('varnames', '^foo$')

  when: foo is defined

Walter
--
Walter Rowe, Division Chief
Infrastructure Services, OISM
Mobile: 202.355.4123

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