add json provider interface

docs/api.rst

@@ -236,21 +236,15 @@ JSON Support
 
 .. module:: flask.json
 
-Flask uses the built-in :mod:`json` module for handling JSON. It will
-use the current blueprint's or application's JSON encoder and decoder
-for easier customization. By default it handles some extra data types:
+Flask uses Python's built-in :mod:`json` module for handling JSON by
+default. The JSON implementation can be changed by assigning a different
+provider to :attr:`flask.Flask.json_provider_class` or
+:attr:`flask.Flask.json`. The functions provided by ``flask.json`` will
+use methods on ``app.json`` if an app context is active.
 
--   :class:`datetime.datetime` and :class:`datetime.date` are serialized
-    to :rfc:`822` strings. This is the same as the HTTP date format.
--   :class:`uuid.UUID` is serialized to a string.
--   :class:`dataclasses.dataclass` is passed to
-    :func:`dataclasses.asdict`.
--   :class:`~markupsafe.Markup` (or any object with a ``__html__``
-    method) will call the ``__html__`` method to get a string.
-
-Jinja's ``|tojson`` filter is configured to use Flask's :func:`dumps`
-function. The filter marks the output with ``|safe`` automatically. Use
-the filter to render data inside ``<script>`` tags.
+Jinja's ``|tojson`` filter is configured to use the app's JSON provider.
+The filter marks the output with ``|safe``. Use it to render data inside
+HTML ``<script>`` tags.
 
 .. sourcecode:: html+jinja
 
@@ -269,6 +263,14 @@ the filter to render data inside ``<script>`` tags.
 
 .. autofunction:: load
 
+.. autoclass:: flask.json.provider.JSONProvider
+    :members:
+    :member-order: bysource
+
+.. autoclass:: flask.json.provider.DefaultJSONProvider
+    :members:
+    :member-order: bysource
+
 .. autoclass:: JSONEncoder
    :members:
 

docs/config.rst

@@ -301,6 +301,10 @@ The following configuration values are used internally by Flask:
 
     Default: ``True``
 
+    .. deprecated:: 2.2
+        Will be removed in Flask 2.3. Set ``app.json.ensure_ascii``
+        instead.
+
 .. py:data:: JSON_SORT_KEYS
 
     Sort the keys of JSON objects alphabetically. This is useful for caching
@@ -310,19 +314,30 @@ The following configuration values are used internally by Flask:
 
     Default: ``True``
 
+    .. deprecated:: 2.2
+        Will be removed in Flask 2.3. Set ``app.json.sort_keys``
+        instead.
+
 .. py:data:: JSONIFY_PRETTYPRINT_REGULAR
 
-    ``jsonify`` responses will be output with newlines, spaces, and indentation
-    for easier reading by humans. Always enabled in debug mode.
+    :func:`~flask.jsonify` responses will be output with newlines,
+    spaces, and indentation for easier reading by humans. Always enabled
+    in debug mode.
 
     Default: ``False``
 
+    .. deprecated:: 2.2
+        Will be removed in Flask 2.3. Set ``app.json.compact`` instead.
+
 .. py:data:: JSONIFY_MIMETYPE
 
     The mimetype of ``jsonify`` responses.
 
     Default: ``'application/json'``
 
+    .. deprecated:: 2.2
+        Will be removed in Flask 2.3. Set ``app.json.mimetype`` instead.
+
 .. py:data:: TEMPLATES_AUTO_RELOAD
 
     Reload templates when they are changed. If not set, it will be enabled in
@@ -387,6 +402,12 @@ The following configuration values are used internally by Flask:
 .. versionchanged:: 2.2
     Removed ``PRESERVE_CONTEXT_ON_EXCEPTION``.
 
+.. versionchanged:: 2.2
+    ``JSON_AS_ASCII``, ``JSON_SORT_KEYS``,
+    ``JSONIFY_MIMETYPE``, and ``JSONIFY_PRETTYPRINT_REGULAR`` will be
+    removed in Flask 2.3. The default ``app.json`` provider has
+    equivalent attributes instead.
+
 
 Configuring from Python Files
 -----------------------------