vars_files depending on host vars no longer fails as of 2.15 with error_on_undefined_vars disabled

[sivel]

Summary

As of #80171 VariableManager.get_vars is no longer responsible for calculating delegated_vars, and instead that is deferred to the TaskExecutor to call VariableManager.get_delegated_vars_and_hostname explicitly. As a result include_delegate_to changed it's default to False since it no longer handles this functionality.

However, when loading vars_files we have some logic that made a potential non-exact determination that the failure could be related to not having a host or needing a delegated host:

ansible/lib/ansible/vars/manager.py

Lines 370 to 373 in 6221109

	# if include_delegate_to is set to False or we don't have a host, we ignore the missing
	# vars file here because we're working on a delegated host or require host vars, see NOTE above
	if include_delegate_to and host:
	raise AnsibleFileNotFound("vars file %s was not found" % vars_file_item)

I'm pretty sure that logic wasn't capable of making the real determination anyway that the missing var was due to missing host vars or facts, and it seems to have been more a guess.

As a result, we never fail, regardless of error_on_undefined_vars being disabled.

This code is also suspect, and I don't think capable of making a proper determination of whether it was host vars vs facts, or anything else pretty much:

ansible/lib/ansible/vars/manager.py

Lines 374 to 377 in 6221109

	except (UndefinedError, AnsibleUndefinedVariable):
	if host is not None and self._fact_cache.get(host.name, dict()).get('module_setup') and task is not None:
	raise AnsibleUndefinedVariable("an undefined variable was found when attempting to template the vars_files item '%s'"
	% vars_file_item, obj=vars_file_item)

Honestly, I'm kind of sad I went looking for this, I've waffled about ignoring it, but the fact that we have code that I don't think is actually capable of doing what it was intended to do bothers me.

Maybe we just always allow it to skip (with a message), and never make it an error, and allow the fact that any vars from that file would be missing, and would cause a failure later. Also, for the record I'm also advocating that we deprecate and remove DEFAULT_UNDEFINED_VAR_BEHAVIOR.

Issue Type

Bug Report

Component Name

lib/ansible/vars/manager.py

Ansible Version

$ ansible --version
2.15

Configuration

# if using a version older than ansible-core 2.12 you should omit the '-t all'
$ ansible-config dump --only-changed -t all
DEFAULT_UNDEFINED_VAR_BEHAVIOR(.../ansible.cfg) = False

OS / Environment

N/A

Steps to Reproduce

- hosts: localhost
  gather_facts: false
  vars_files:
    - '{{ foo }}'

Expected Results

ERROR! vars file {{ foo }} was not found
Could not find file on the Ansible Controller.
If you are using a module and expect the file to exist on the remote, see the remote_src option

Actual Results

No failure, and no indication of skipping loading the file.

Code of Conduct

• I agree to follow the Ansible Code of Conduct

[ansibot]

Files identified in the description:

• lib/ansible/vars/manager.py

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

click here for bot help

[sivel]

So I guess to extend this, a few options:

1. Never fail, always skip, rely on a task later using a var from the vars file to fail due to missing var
2. Skip only when get_vars is called for the play itself, and always fail if there is a task/host.
3. Fail always, but this would prevent using host_vars for later templating