add docs for the vardict module utils (#8460)

* add docs for the vardict module utils

* fix var name

* add entry to BOTMETA

* rollback adjustment in deps guide

* Update docs/docsite/rst/guide_vardict.rst

Co-authored-by: Felix Fontein <felix@fontein.de>

* adjustments

* Update docs/docsite/rst/guide_vardict.rst

Co-authored-by: Felix Fontein <felix@fontein.de>

---------

Co-authored-by: Felix Fontein <felix@fontein.de>

.github/BOTMETA.yml

@@ -1462,6 +1462,8 @@ files:
     maintainers: $team_scaleway
   docs/docsite/rst/guide_deps.rst:
     maintainers: russoz
+  docs/docsite/rst/guide_vardict.rst:
+    maintainers: russoz
   docs/docsite/rst/test_guide.rst:
     maintainers: felixfontein
 #########################

docs/docsite/extra-docs.yml

@@ -17,3 +17,4 @@ sections:
   - title: Developer Guides
     toctree:
       - guide_deps
+      - guide_vardict

docs/docsite/rst/guide_vardict.rst

@@ -0,0 +1,176 @@
+..
+  Copyright (c) Ansible Project
+  GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+  SPDX-License-Identifier: GPL-3.0-or-later
+
+.. _ansible_collections.community.general.docsite.guide_vardict:
+
+VarDict Guide
+=============
+
+Introduction
+^^^^^^^^^^^^
+
+The ``ansible_collections.community.general.plugins.module_utils.vardict`` module util provides the
+``VarDict`` class to help manage the module variables. That class is a container for module variables,
+especially the ones for which the module must keep track of state changes, and the ones that should
+be published as return values.
+
+Each variable has extra behaviors controlled by associated metadata, simplifying the generation of
+output values from the module.
+
+Quickstart
+""""""""""
+
+The simplest way of using ``VarDict`` is:
+
+.. code-block:: python
+
+    from ansible_collections.community.general.plugins.module_utils.vardict import VarDict
+
+Then in ``main()``, or any other function called from there:
+
+.. code-block:: python
+
+    vars = VarDict()
+
+    # Next 3 statements are equivalent
+    vars.abc = 123
+    vars["abc"] = 123
+    vars.set("abc", 123)
+
+    vars.xyz = "bananas"
+    vars.ghi = False
+
+And by the time the module is about to exit:
+
+.. code-block:: python
+
+    results = vars.output()
+    module.exit_json(**results)
+
+That makes the return value of the module:
+
+.. code-block:: javascript
+
+    {
+        "abc": 123,
+        "xyz": "bananas",
+        "ghi": false
+    }
+
+Metadata
+""""""""
+
+The metadata values associated with each variable are:
+
+- ``output: bool`` - marks the variable for module output as a module return value.
+- ``fact: bool`` - marks the variable for module output as an Ansible fact.
+- ``verbosity: int`` - sets the minimum level of verbosity for which the variable will be included in the output.
+- ``change: bool`` - controls the detection of changes in the variable value.
+- ``initial_value: any`` - when using ``change`` and need to forcefully set an intial value to the variable.
+- ``diff: bool`` - used along with ``change``, this generates an Ansible-style diff ``dict``.
+
+See the sections below for more details on how to use the metadata.
+
+
+Using VarDict
+^^^^^^^^^^^^^
+
+Basic Usage
+"""""""""""
+
+As shown above, variables can be accessed using the ``[]`` operator, as in a ``dict`` object,
+and also as an object attribute, such as ``vars.abc``. The form using the ``set()``
+method is special in the sense that you can use it to set metadata values:
+
+.. code-block:: python
+
+    vars.set("abc", 123, output=False)
+    vars.set("abc", 123, output=True, change=True)
+
+Another way to set metadata after the variables have been created is:
+
+.. code-block:: python
+
+    vars.set_meta("abc", output=False)
+    vars.set_meta("abc", output=True, change=True, diff=True)
+
+You can use either operator and attribute forms to access the value of the variable. Other ways to
+access its value and its metadata are:
+
+.. code-block:: python
+
+    print("abc value = {0}".format(vars.var("abc")["value"]))        # get the value
+    print("abc output? {0}".format(vars.get_meta("abc")["output"]))  # get the metadata like this
+
+The names of methods, such as ``set``, ``get_meta``, ``output`` amongst others, are reserved and
+cannot be used as variable names. If you try to use a reserved name a ``ValueError`` exception
+is raised with the message "Name <var> is reserved".
+
+Generating output
+"""""""""""""""""
+
+By default, every variable create will be enable for output with minimum verbosity set to zero, in
+other words, they will always be in the output by default.
+
+You can control that when creating the variable for the first time or later in the code:
+
+.. code-block:: python
+
+    vars.set("internal", x + 4, output=False)
+    vars.set_meta("internal", output=False)
+
+You can also set the verbosity of some variable, like:
+
+.. code-block:: python
+
+    vars.set("abc", x + 4)
+    vars.set("debug_x", x, verbosity=3)
+
+    results = vars.output(module._verbosity)
+    module.exit_json(**results)
+
+If the module was invoked with verbosity lower than 3, then the output will only contain
+the variable ``abc``. If running at higher verbosity, as in ``ansible-playbook -vvv``,
+then the output will also contain ``debug_x``.
+
+Generating facts is very similar to regular output, but variables are not marked as facts by default.
+
+.. code-block:: python
+
+    vars.set("modulefact", x + 4, fact=True)
+    vars.set("debugfact", x, fact=True, verbosity=3)
+
+    results = vars.output(module._verbosity)
+    results["ansible_facts"] = {"module_name": vars.facts(module._verbosity)}
+    module.exit_json(**results)
+
+Handling change
+"""""""""""""""
+
+You can use ``VarDict`` to determine whether variables have had their values changed.
+
+.. code-block:: python
+
+    vars.set("abc", 42, change=True)
+    vars.abc = 90
+
+    results = vars.output()
+    results["changed"] = vars.has_changed
+    module.exit_json(**results)
+
+If tracking changes in variables, you may want to present the difference between the initial and the final
+values of it. For that, you want to use:
+
+.. code-block:: python
+
+    vars.set("abc", 42, change=True, diff=True)
+    vars.abc = 90
+
+    results = vars.output()
+    results["changed"] = vars.has_changed
+    results["diff"] = vars.diff()
+    module.exit_json(**results)
+
+.. versionadded:: 6.1.0