Collection requirements: mention idepmotency explicitly (#220)

collection_checklist.md

@@ -18,6 +18,7 @@ Note for reviewers: If you don't know how to check any of the points below, plea
 - [ ] follows [licensing rules](https://github.com/ansible-collections/overview/blob/main/collection_requirements.rst#licensing)
 - [ ] follows the [Ansible documentation standards](https://docs.ansible.com/ansible/devel/dev_guide/developing_modules_documenting.html) and the [style guide](https://docs.ansible.com/ansible/devel/dev_guide/style_guide/index.html#style-guide)
 - [ ] follows [development conventions](https://docs.ansible.com/ansible/devel/dev_guide/developing_modules_best_practices.html); as well as these other requirements:
+  - [ ] modules satisfy the concept of [idempotency](https://docs.ansible.com/ansible/latest/reference_appendices/glossary.html#term-Idempotency>)
   - [ ] modules that only gather information are named `<something>_info`
   - [ ] modules that return `ansible_facts` are named `<something>_facts` and do not return non-facts
   - [ ] other modules must not allow querying information using specific `state` option values, or similar mechanisms (like `state=get` or `state=query`).  These features should be moved to `<something>_info` or `<something>_fact` modules.

collection_requirements.rst

@@ -382,9 +382,10 @@ Development conventions
 
 Besides all the requirements listed in the `Development conventions <https://docs.ansible.com/ansible/devel/dev_guide/developing_modules_best_practices.html>`_, be sure:
 
+* Your modules satisfy the concept of `idempotency <https://docs.ansible.com/ansible/latest/reference_appendices/glossary.html#term-Idempotency>`_: if a module repeatedly runs with the same set of inputs, it will not make any changes on the system.
 * Your modules do not query information using special ``state`` option values like ``get``, ``list``, ``query``, or ``info`` -
-  create new ``_info`` or ``_facts`` modules instead (for more information, refer to the `Developing modules guidelines <https://docs.ansible.com/ansible/devel/dev_guide/developing_modules_general.html#creating-an-info-or-a-facts-module>`_)
-* ``check_mode`` is supported in all ``*_info`` and ``*_facts`` modules (for more information, refer to the `Development conventions <https://docs.ansible.com/ansible/devel/dev_guide/developing_modules_best_practices.html#following-ansible-conventions>`_)
+  create new ``_info`` or ``_facts`` modules instead (for more information, refer to the `Developing modules guidelines <https://docs.ansible.com/ansible/devel/dev_guide/developing_modules_general.html#creating-an-info-or-a-facts-module>`_).
+* ``check_mode`` is supported in all ``*_info`` and ``*_facts`` modules (for more information, refer to the `Development conventions <https://docs.ansible.com/ansible/devel/dev_guide/developing_modules_best_practices.html#following-ansible-conventions>`_).
 
 .. _collection_dependencies: