Fixed #17648 -- Add for_concrete_model to GenericForeignKey.

Allows a `GenericForeignKey` to reference proxy models. The default
for `for_concrete_model` is `True` to keep backwards compatibility.

Also added the analog `for_concrete_model` kwarg to
`generic_inlineformset_factory` to provide an API at the form level.

tests/generic_relations/tests.py

@@ -6,7 +6,9 @@ from django.contrib.contenttypes.models import ContentType
 from django.test import TestCase
 
 from .models import (TaggedItem, ValuableTaggedItem, Comparison, Animal,
-    Vegetable, Mineral, Gecko, Rock, ManualPK)
+                     Vegetable, Mineral, Gecko, Rock, ManualPK,
+                     ForProxyModelModel, ForConcreteModelModel,
+                     ProxyRelatedModel, ConcreteRelatedModel)
 
 
 class GenericRelationsTests(TestCase):
@@ -256,12 +258,120 @@ class TaggedItemForm(forms.ModelForm):
         widgets = {'tag': CustomWidget}
 
 class GenericInlineFormsetTest(TestCase):
-    """
-    Regression for #14572: Using base forms with widgets
-    defined in Meta should not raise errors.
-    """
-
     def test_generic_inlineformset_factory(self):
+        """
+        Regression for #14572: Using base forms with widgets
+        defined in Meta should not raise errors.
+        """
         Formset = generic_inlineformset_factory(TaggedItem, TaggedItemForm)
         form = Formset().forms[0]
         self.assertIsInstance(form['tag'].field.widget, CustomWidget)
+
+    def test_save_new_for_proxy(self):
+        Formset = generic_inlineformset_factory(ForProxyModelModel,
+            fields='__all__', for_concrete_model=False)
+
+        instance = ProxyRelatedModel.objects.create()
+
+        data = {
+            'form-TOTAL_FORMS': '1',
+            'form-INITIAL_FORMS': '0',
+            'form-MAX_NUM_FORMS': '',
+            'form-0-title': 'foo',
+        }
+
+        formset = Formset(data, instance=instance, prefix='form')
+        self.assertTrue(formset.is_valid())
+
+        new_obj, = formset.save()
+        self.assertEqual(new_obj.obj, instance)
+
+    def test_save_new_for_concrete(self):
+        Formset = generic_inlineformset_factory(ForProxyModelModel,
+            fields='__all__', for_concrete_model=True)
+
+        instance = ProxyRelatedModel.objects.create()
+
+        data = {
+            'form-TOTAL_FORMS': '1',
+            'form-INITIAL_FORMS': '0',
+            'form-MAX_NUM_FORMS': '',
+            'form-0-title': 'foo',
+        }
+
+        formset = Formset(data, instance=instance, prefix='form')
+        self.assertTrue(formset.is_valid())
+
+        new_obj, = formset.save()
+        self.assertNotIsInstance(new_obj.obj, ProxyRelatedModel)
+
+
+class ProxyRelatedModelTest(TestCase):
+    def test_default_behavior(self):
+        """
+        The default for for_concrete_model should be True
+        """
+        base = ForConcreteModelModel()
+        base.obj = rel = ProxyRelatedModel.objects.create()
+        base.save()
+
+        base = ForConcreteModelModel.objects.get(pk=base.pk)
+        rel = ConcreteRelatedModel.objects.get(pk=rel.pk)
+        self.assertEqual(base.obj, rel)
+
+    def test_works_normally(self):
+        """
+        When for_concrete_model is False, we should still be able to get
+        an instance of the concrete class.
+        """
+        base = ForProxyModelModel()
+        base.obj = rel = ConcreteRelatedModel.objects.create()
+        base.save()
+
+        base = ForProxyModelModel.objects.get(pk=base.pk)
+        self.assertEqual(base.obj, rel)
+
+    def test_proxy_is_returned(self):
+        """
+        Instances of the proxy should be returned when
+        for_concrete_model is False.
+        """
+        base = ForProxyModelModel()
+        base.obj = ProxyRelatedModel.objects.create()
+        base.save()
+
+        base = ForProxyModelModel.objects.get(pk=base.pk)
+        self.assertIsInstance(base.obj, ProxyRelatedModel)
+
+    def test_query(self):
+        base = ForProxyModelModel()
+        base.obj = rel = ConcreteRelatedModel.objects.create()
+        base.save()
+
+        self.assertEqual(rel, ConcreteRelatedModel.objects.get(bases__id=base.id))
+
+    def test_query_proxy(self):
+        base = ForProxyModelModel()
+        base.obj = rel = ProxyRelatedModel.objects.create()
+        base.save()
+
+        self.assertEqual(rel, ProxyRelatedModel.objects.get(bases__id=base.id))
+
+    def test_generic_relation(self):
+        base = ForProxyModelModel()
+        base.obj = ProxyRelatedModel.objects.create()
+        base.save()
+
+        base = ForProxyModelModel.objects.get(pk=base.pk)
+        rel = ProxyRelatedModel.objects.get(pk=base.obj.pk)
+        self.assertEqual(base, rel.bases.get())
+
+    def test_generic_relation_set(self):
+        base = ForProxyModelModel()
+        base.obj = ConcreteRelatedModel.objects.create()
+        base.save()
+        newrel = ConcreteRelatedModel.objects.create()
+
+        newrel.bases = [base]
+        newrel = ConcreteRelatedModel.objects.get(pk=newrel.pk)
+        self.assertEqual(base, newrel.bases.get())