README.md

Given tasks like

- command: foo
  when: foo_condition
  register: foo_result
  
- changelog: msg="ran foo"
  when: foo_result|changed
  
- command: bar
  when: bar_condition
  register: bar_result
  
- changelog: msg="ran bar"
  when: bar_result|changed

I want the changelog action to run

• if both foo_condition and bar_condition were true:

new-changelog-entry "ran foo"
new-changelog-entry -a "ran bar"

• if foo_condition was true and bar_condition was false:

new-changelog-entry "ran foo"

• if foo_condition was false and bar_condition was true:

new-changelog-entry "ran bar"

It should, of course, work with more than just two entries.

action_plugins-changelog.py

# action_plugins/changelog.py
from ansible.runner.action_plugins import normal
from ansible.runner.return_data import ReturnData


class ActionModule(normal.ActionModule):
    '''Add entries to /root/Changelog'''

    def run(self, conn, tmp, module_name, module_args, inject, complex_args=None, **kwargs):
        if self.runner.noop_on_check(inject):
            return ReturnData(conn=conn, comm_ok=True, result=dict(skipped=True, msg='check mode not supported for this module'))
        host = inject['inventory_hostname']
        changelog_started = inject['hostvars'][host].get('changelog_started', False)
        complex_args.setdefault('append', changelog_started)
        return super(ActionModule, self).run(conn, tmp, module_name, module_args, inject, complex_args=complex_args, **kwargs)

library-changelog.py

#!/usr/bin/python
# library/changelog.py
import os
import subprocess
from ansible.module_utils.basic import *  # noqa


DOCUMENTATION = '''
---
module: changelog
short_description: appends a message to /root/Changelog
description:
  - The M(changelog) module takes single a string message and appends it
    to /root/Changelog on the remote host, with a date and time header.
  - This requires pov-admin-tools to be installed on the remote.
options:
  msg:
    description:
      - the message
    required: true
    default: null
  append:
    description:
      - append the message to the existing entry instead of starting a new entry
    required: false
    default: false for the 1st invocation on each host, true for all subsequent invocations
author:
  - Marius Gedminas <[email protected]>
'''

EXAMPLES = '''
# Prerequisite: install pov-admin-tools from ppa:pov
- apt_repository: repo='ppa:pov' state=present
- apt: name=pov-admin-tools state=present

# Record new installed package iff it was installed
- apt: name=postfix state=present
  record: apt_result
- changelog: msg="apt-get install postfix"
  when: apt_result|changed
'''


def main():
    module = AnsibleModule(
        argument_spec=dict(
            msg=dict(),
            append=dict(type='bool', default=False)
        ),
    )
    msg = module.params['msg']
    append = module.params['append']
    if msg in ('-a', '-e', '/root/Changelog') or os.path.exists(msg):
        module.fail_json(msg="message cannot be '{}' due to the way new-changelog-message parses its arguments".format(msg))
    args = ['new-changelog-entry']
    if append:
        args += ['-a']
    args += [msg]
    try:
        cmd = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        out, err = cmd.communicate()
        rc = cmd.returncode
    except (OSError, IOError) as e:
        module.fail_json(rc=e.errno, msg=str(e), cmd=args)
    module.exit_json(
        message=msg,
        rc=rc,
        out=out,
        err=err,
        changed=True,
        ansible_facts=dict(
            changelog_started=True,
        )
    )


if __name__ == '__main__':
    main()