Update inventory caching documentation (#69100)

docs/docsite/rst/dev_guide/developing_plugins.rst

@@ -150,7 +150,7 @@ see the source code for the `action plugins included with Ansible Core <https://
 Cache plugins
 -------------
 
-Cache plugins store gathered facts and data retrieved by inventory plugins. Only fact caching is currently supported by cache plugins in collections.
+Cache plugins store gathered facts and data retrieved by inventory plugins.
 
 Import cache plugins using the cache_loader so you can use ``self.set_options()`` and ``self.get_option(<option_name>)``. If you import a cache plugin directly in the code base, you can only access options via ``ansible.constants``, and you break the cache plugin's ability to be used by an inventory plugin.
 

docs/docsite/rst/plugins/cache.rst

@@ -90,7 +90,14 @@ or if the inventory plugin accepts a YAML configuration source, in the configura
 
 To cache inventory with a custom plugin in your plugin path, follow the :ref:`developer guide on cache plugins<developing_cache_plugins>`.
 
-You can use any cache plugin shipped with Ansible to cache inventory, but you cannot use a cache plugin inside a collection. If you enable caching for inventory plugins without selecting an inventory-specific cache plugin, Ansible falls back to caching inventory with the fact cache plugin you configured. Consult the individual inventory plugin documentation or the Ansible :ref:`configuration <ansible_configuration_settings>` for more details.
+To cache inventory with a cache plugin in a collection, use the FQCN:
+
+.. code-block:: ini
+
+   [inventory]
+   cache_plugin=collection_namespace.collection_name.cache_plugin
+
+If you enable caching for inventory plugins without selecting an inventory-specific cache plugin, Ansible falls back to caching inventory with the fact cache plugin you configured. Consult the individual inventory plugin documentation or the Ansible :ref:`configuration <ansible_configuration_settings>` for more details.
 
 .. Note: In Ansible 2.7 and earlier, inventory plugins can only use file-based cache plugins, such as jsonfile, pickle, and yaml.
 

docs/docsite/rst/plugins/inventory.rst

@@ -152,7 +152,7 @@ Here is an example of setting inventory caching with some fact caching defaults
    cache = yes
    cache_connection = /tmp/ansible_inventory
 
-Besides cache plugins shipped with Ansible, cache plugins eligible for caching inventory can also reside in a custom cache plugin path. Cache plugins in collections are not supported yet for inventory.
+Besides cache plugins shipped with Ansible, cache plugins eligible for caching inventory can also reside in a custom cache plugin path or in a collection. Use FQCN if the cache plugin is in a collection.
 
 .. _inventory_plugin_list:
 

docs/docsite/rst/porting_guides/porting_guide_2.10.rst

@@ -148,6 +148,7 @@ Lookup plugin names case-sensitivity
 Noteworthy plugin changes
 -------------------------
 
+* Cache plugins in collections can be used to cache data from inventory plugins. Previously, cache plugins in collections could only be used for fact caching.
 * The ``hashi_vault`` lookup plugin now returns the latest version when using the KV v2 secrets engine. Previously, it returned all versions of the secret which required additional steps to extract and filter the desired version.
 * Some undocumented arguments from ``FILE_COMMON_ARGUMENTS`` have been removed; plugins using these, in particular action plugins, need to be adjusted. The undocumented arguments which were removed are ``src``, ``follow``, ``force``, ``content``, ``backup``, ``remote_src``, ``regexp``, ``delimiter``, and ``directory_mode``.