Callback answer feature (#1091)

* Added callback answer feature

* Fixed typehints and tests

* Make context manager in tests compatible with Python 3.8

docs/utils/callback_answer.rst

@@ -0,0 +1,106 @@
+.. _callback-answer-util:
+===============
+Callback answer
+===============
+
+Helper for callback query handlers, can be useful in bots with a lot of callback
+handlers to automatically take answer to all requests.
+
+Simple usage
+============
+
+For use, it is enough to register the inner middleware :class:`aiogram.utils.callback_answer.CallbackAnswerMiddleware` in dispatcher or specific router:
+
+.. code-block:: python
+
+    dispatcher.callback_query.middleware(CallbackAnswerMiddleware())
+
+After that all handled callback queries will be answered automatically after processing the handler.
+
+Advanced usage
+==============
+
+In some cases you need to have some non-standard response parameters, this can be done in several ways:
+
+Global defaults
+---------------
+
+Change default parameters while initializing middleware, for example change answer to `pre` mode and text "OK":
+
+.. code-block:: python
+
+    dispatcher.callback_query.middleware(CallbackAnswerMiddleware(pre=True, text="OK"))
+
+
+Look at :class:`aiogram.utils.callback_answer.CallbackAnswerMiddleware` to get all available parameters
+
+
+Handler specific
+----------------
+
+By using :ref:`flags <flags>` you can change the behavior for specific handler
+
+.. code-block:: python
+
+    @router.callback_query(<filters>)
+    @flags.callback_answer(text="Thanks", cache_time=30)
+    async def my_handler(query: CallbackQuery):
+        ...
+
+Flag arguments is the same as in :class:`aiogram.utils.callback_answer.CallbackAnswerMiddleware`
+with additional one :code:`disabled` to disable answer.
+
+A special case
+--------------
+
+It is not always correct to answer the same in every case,
+so there is an option to change the answer inside the handler. You can get an instance of :class:`aiogram.utils.callback_answer.CallbackAnswer` object inside handler and change whatever you want.
+
+.. danger::
+
+    Note that is impossible to change callback answer attributes when you use :code:`pre=True` mode.
+
+.. code-block:: python
+
+    @router.callback_query(<filters>)
+    async def my_handler(query: CallbackQuery, callback_answer: CallbackAnswer):
+        ...
+        if <everything is ok>:
+            callback_answer.text = "All is ok"
+        else:
+            callback_answer.text = "Something wrong"
+            callback_answer.cache_time = 10
+
+
+Combine that all at once
+------------------------
+
+For example you want to answer in most of cases before handler with text "🤔" but at some cases need to answer after the handler with custom text,
+so you can do it:
+
+.. code-block:: python
+
+    dispatcher.callback_query.middleware(CallbackAnswerMiddleware(pre=True, text="🤔"))
+
+    @router.callback_query(<filters>)
+    @flags.callback_answer(pre=False, cache_time=30)
+    async def my_handler(query: CallbackQuery):
+        ...
+        if <everything is ok>:
+            callback_answer.text = "All is ok"
+
+
+Description of objects
+======================
+
+.. autoclass:: aiogram.utils.callback_answer.CallbackAnswerMiddleware
+    :show-inheritance:
+    :member-order: bysource
+    :special-members: __init__
+    :members:
+
+.. autoclass:: aiogram.utils.callback_answer.CallbackAnswer
+    :show-inheritance:
+    :member-order: bysource
+    :special-members: __init__
+    :members:

docs/utils/index.rst

@@ -8,3 +8,4 @@ Utils
     i18n
     chat_action
     web_app
+    callback_answer