Setting a variable to default(omit) sets it to a string placeholder instead of undefined

[loop-evgeny]

SUMMARY

When I set a variable to anothervariable | default(omit) and anothervariable is undefined I expect the result to be undefined, but instead it's set to a string placeholder ("__omit_place_holder__SOMEGUID").

ISSUE TYPE

• Bug Report

COMPONENT NAME

Jinja2 expressions?

ANSIBLE VERSION

ansible 2.6.2
  config file = /media/sf_work/lops/ansible.cfg
  configured module search path = [u'/home/em/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/dist-packages/ansible
  executable location = /usr/bin/ansible
  python version = 2.7.12 (default, Dec  4 2017, 14:50:18) [GCC 5.4.0 20160609]

CONFIGURATION

No changes

OS / ENVIRONMENT

Ubuntu 16.04

STEPS TO REPRODUCE

- hosts: all
  gather_facts: false
  connection: local
  vars:
    stillmissing: "{{ missingvar | default(omit) }}"
  tasks:
  - debug:
      msg: "stillmissing = {{ stillmissing | default('still not defined') }}"

EXPECTED RESULTS

"msg": "stillmissing = still not defined"

ACTUAL RESULTS

"msg": "stillmissing = __omit_place_holder__5ebe2a97fd59a2b8a8f0f9772e8e675496a74faa"

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Files identified in the description:

• lib/ansible/modules/files/template.py

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[ansibot]

Files identified in the description:
None

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[loop-evgeny]

default(None) also doesn't work to leave the variable undefined - it gets converted to an empty string

[sivel]

This is the expected behavior. omit is a special variable for omitting an individual argument to a module with only that value, and not for any more generic process. An Example:

- ping:
    data: "{{ omit }}"

It is not designed to leave a variable undefined. The documentation describes it as:

As of Ansible 1.8, it is possible to use the default filter to omit module parameters using the special omit variable

There is actually no way to define a variable as undefined. The act of defining it, will always define it, regardless of your value. You will need to use additional logic to handle your situation.

If you have further questions please stop by IRC or the mailing list:

• IRC: #ansible on irc.freenode.net
• mailing list: https://groups.google.com/forum/#!forum/ansible-project

[loop-evgeny]

The string "__omit_place_holder__5ebe2a97fd59a2b8a8f0f9772e8e675496a74faa" is expected behavior? What user could possibly expect that?

There is actually no way to define a variable as undefined.

That's a problem. "Defining an undefined variable" sounds like a strange use case, but it's not, for example, if you just want to copy one variable to another, especially a dictionary: keys that were not in the input dictionary should not be in the output one.

[bcoca]

omit is not for 'undefining variables' it is for 'omitting' action options, as such its is hard to meet 'expectations' when it is being misused.

If you want to 'null' a variable, this can be done (yaml ~ or python None will work), but you cannot 'undefine' it. Still, this would be a 'feature' request, not a bug, but considering that the underlying technologies used also don't permit this, it is not something trivial to implement.

[loop-evgeny]

Looks like there is already a feature request for this: #22417 (I couldn't find it before).

I would say that the current behaviour is still a bug, regardless of what happens with that feature request. If using omit in this way is not allowed then Ansible should produce an error, rather than proceed with the wrong data.

[bcoca]

we cannot know how you will use a variable until the play has ended, by that time that information is irrelevant. So having omit value in a variable is not incorrect nor wrong, the usage of it might be, but that is not something we can know at the time of the value assignment.

[loop-evgeny]

So having omit value in a variable is not incorrect nor wrong

I see what you're saying, but seeing the string value "__omit_place_holder__5ebe2a97fd59a2b8a8f0f9772e8e675496a74faa" is never the expected behaviour.

I ran into this again yesterday where I tried something similar with the "mode" variable of the "file" module. What happened was that the mode was simply left unchanged (instead of the | default('0700') being used). This is a real trap that I'm sure many others have fallen into.

It's hard to know without digging into the implementation, but surely you can detect when the variable is being evaluated to its string value and that string value is the omit placeholder?

Even if you error after the play has ended that's much better than silently getting the wrong result, as I did with the mode, so no, I don't think it's "irrelevant".