Fixed #23656 -- Made FormMixin.get_form's form_class argument optional.

Thanks Tim Graham for the review.

docs/internals/deprecation.txt

@@ -65,6 +65,9 @@ about each item can often be found in the release notes of two versions prior.
 * The ``original_content_type_id`` attribute on
   ``django.contrib.admin.helpers.InlineAdminForm`` will be removed.
 
+* The backwards compatibility shim to allow ``FormMixin.get_form()`` to be
+  defined with no default value for its ``form_class`` argument will be removed.
+
 .. _deprecation-removed-in-1.9:
 
 1.9

docs/ref/class-based-views/mixins-editing.txt

@@ -49,10 +49,15 @@ FormMixin
         Retrieve the form class to instantiate. By default
         :attr:`.form_class`.
 
-    .. method:: get_form(form_class)
+    .. method:: get_form(form_class=None)
 
         Instantiate an instance of ``form_class`` using
         :meth:`~django.views.generic.edit.FormMixin.get_form_kwargs`.
+        If ``form_class`` isn't provided :meth:`get_form_class` will be used.
+
+        .. versionchanged:: 1.8
+
+            The ``form_class`` argument is not required anymore.
 
     .. method:: get_form_kwargs()
 

docs/releases/1.8.txt

@@ -242,6 +242,10 @@ Generic Views
   :meth:`~django.views.generic.detail.SingleObjectMixin.get_object()`
   so that it'll perform its lookup using both the primary key and the slug.
 
+* The :meth:`~django.views.generic.edit.FormMixin.get_form()` method doesn't
+  require a ``form_class`` to be provided anymore. If not provided ``form_class``
+  defaults to :meth:`~django.views.generic.edit.FormMixin.get_form_class()`.
+
 Internationalization
 ^^^^^^^^^^^^^^^^^^^^
 
@@ -892,3 +896,10 @@ The ``original_content_type_id`` attribute on ``InlineAdminForm`` has been
 deprecated and will be removed in Django 2.0. Historically, it was used
 to construct the "view on site" URL. This URL is now accessible using the
 ``absolute_url`` attribute of the form.
+
+``django.views.generic.edit.FormMixin.get_form()``’s ``form_class`` argument
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``FormMixin`` subclasses that override the ``get_form()`` method should make
+sure to provide a default value for the ``form_class`` argument since it's
+now optional.

docs/topics/class-based-views/mixins.txt

@@ -463,16 +463,14 @@ Our new ``AuthorDetail`` looks like this::
 
         def get_context_data(self, **kwargs):
             context = super(AuthorDetail, self).get_context_data(**kwargs)
-            form_class = self.get_form_class()
-            context['form'] = self.get_form(form_class)
+            context['form'] = self.get_form()
             return context
 
         def post(self, request, *args, **kwargs):
             if not request.user.is_authenticated():
                 return HttpResponseForbidden()
             self.object = self.get_object()
-            form_class = self.get_form_class()
-            form = self.get_form(form_class)
+            form = self.get_form()
             if form.is_valid():
                 return self.form_valid(form)
             else: