ansible: Respect interpreter_python config

[extmind]

Use the global configuration variable interpreter_python when ansible_python_interpreter is unset.

Fixes #740

Edit: @moreati clarify config vs variable distinction

[stefanor]

@moreati: Thanks for the more frequent releases.

This is one of the patches that Debian has been carrying for a while. As we don't have a /usr/bin/python in the distro any more, it's common to have interpreter_python configured. I'd appreciate it if you would re-review this PR.

[moreati]

Sorry for the long wait. I've been avoiding the interpreter discovery code for far too long. I've now tackled most of templating connection options/variables and connection timeout, and I have a mcuh better understanding of the ... intricacies.

This patch looks broadly correct. I'm going to update for master, rejig a couple of details, and add some tests.

[moreati]

The failure in https://github.com/mitogen-hq/mitogen/actions/runs/12412205309/job/34651500318?pr=833

TASK [assert_equal left=out.result[0].kwargs.python_path, right=['{{out.discovered_interpreter}}']] ***
Thursday 19 December 2024  12:07:55 +0000 (0:00:00.056)       0:07:56.582 ***** 
fatal: [tc-python-path-hostvar]: FAILED! => changed=false 
  msg: |-
    Lists differ: ['/hostvar/path/to/python'] != [False]
  
    First differing element 0:
    '/hostvar/path/to/python'
    False
  
    - ['/hostvar/path/to/python']
    + [False]

is perplexng. The test is expecting ansible_mitogen.plugins.action.mitogen_get_stack.ActionModule()._connection._action._discovered_interpreter == u'/hostvar/path/to/python'. However that value could only come from

mitogen/tests/ansible/hosts/transport_config.hosts

Lines 36 to 38 in e8005ec

	[tc_python_path]
	tc-python-path-unset
	tc-python-path-hostvar ansible_python_interpreter=/hostvar/path/to/python

which by definition makes it not a discovered python interpreter.

I need to confirm the semantics of ansible.plugins.ActionBase._discovered_python in vanilla Ansible.

[moreati]

Going by ansible/ansible@4d3a612#diff-cbe4262a246b2475f3884118713f2ae5a6c49a443d9a942b6c63445bed9354dcR32

• ansible.plugins.action.ActionBase._discovered_interpreter starts False.
• It's assigned the path of an interpreter on the targert if and only if interpreter discvoery is run.
• Assignment to ActionBase._discovered_interpreter is closely tied to populating the variable discovered_interpreter_python.