Is it possible to use an Ansible Core Module within a Custom Module?

There is also this related question "Access predefined ansible modules in custom module" but unfortunately without an helpful answer.

In general, I would like to create a Custom Module which uses some Core Modules.

If I e.g. want to use the Core Module file, I could of course look at the main function and extract the parts needed by importing the functions required.

So to create / remove a file this would require to use something like

from ansible.modules.file import check_owner_exists, check_group_exists, keep_backward_compatibility_on_timestamps, ensure_file_attributes, ensure_absent

Then copy the required code and use it accordingly.

This seems like a huge workaround for something as simple as importing a core module in a custom module.

Are there any better ways to call the file module in a custom module?

As @U880D already pointed out, it is not possible call a module from another module.

The way around this is to use an action plugin (https://docs.ansible.com/ansible/latest/dev_guide/developing_plugins.html#developing-actions. The most prominent example is probably the template module:

• https://github.com/ansible/ansible/blob/devel/lib/ansible/plugins/action/template.py which contains the actual code
• https://github.com/ansible/ansible/blob/devel/lib/ansible/modules/template.py which only contains the documentation

In the hope it simplifies life for others, here is what I ended up using.

So to run the file module inside our own "module" we create library/custom_file.py (the "module" file containing only the documentation) with content

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# Copyright: ...
# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)

DOCUMENTATION = r"""
---
<...>
"""
EXAMPLES = r"""
---
<...>
"""
RETURN = r"""
---
<...>
"""

and action_plugins/custom_file.py with

#!/usr/bin/env python3

from ansible.plugins.action import ActionBase

class ActionModule(ActionBase):
    def run(self, tmp=None, task_vars=None):
        result = super(ActionModule, self).run(tmp, task_vars)

        result.update(self._execute_module(
            module_name="file", module_args=file_args, task_vars=task_vars, tmp=tmp
        ))

        return result

now we can use this "module" in our playbook test.yml

- name: Test my new module
  gather_facts: false
  hosts: localhost
  tasks:
    - name: Run custom file module
      custom_file:
        path: /etc/foo.conf
        owner: foo
        group: foo
        mode: '0644'