[1.9.x] Fixed #25622 -- Accounted for generic relations in the admin to field validation

Thanks to Jonathan Liuti for the report and Tim Graham for the review.

Backport of 9dcfecb7c6 from master

django/contrib/admin/options.py

@@ -413,8 +413,10 @@ class BaseModelAdmin(six.with_metaclass(forms.MediaDefiningClass)):
         )
         for related_object in related_objects:
             related_model = related_object.related_model
+            remote_field = related_object.field.remote_field
             if (any(issubclass(model, related_model) for model in registered_models) and
-                    related_object.field.remote_field.get_related_field() == field):
+                    hasattr(remote_field, 'get_related_field') and
+                    remote_field.get_related_field() == field):
                 return True
 
         return False

docs/releases/1.8.6.txt

@@ -48,3 +48,6 @@ Bugfixes
 * Fixed a regression in ``URLValidator`` that allowed URLs with consecutive
   dots in the domain section (like ``http://example..com/``) to pass
   (:ticket:`25620`).
+
+* Fixed a crash with ``GenericRelation`` and
+  ``BaseModelAdmin.to_field_allowed`` (:ticket:`25622`).

tests/admin_views/admin.py

@@ -31,18 +31,19 @@ from .models import (
     EmptyModelHidden, EmptyModelMixin, EmptyModelVisible, ExplicitlyProvidedPK,
     ExternalSubscriber, Fabric, FancyDoodad, FieldOverridePost,
     FilteredManager, FooAccount, FoodDelivery, FunkyTag, Gadget, Gallery,
-    Grommet, ImplicitlyGeneratedPK, Ingredient, InlineReference, InlineReferer,
+    GenRelReference, Grommet, ImplicitlyGeneratedPK, Ingredient,
-    Inquisition, Language, Link, MainPrepopulated, ModelWithStringPrimaryKey,
+    InlineReference, InlineReferer, Inquisition, Language, Link,
-    NotReferenced, OldSubscriber, OtherStory, Paper, Parent,
+    MainPrepopulated, ModelWithStringPrimaryKey, NotReferenced, OldSubscriber,
-    ParentWithDependentChildren, Person, Persona, Picture, Pizza, Plot,
+    OtherStory, Paper, Parent, ParentWithDependentChildren, Person, Persona,
-    PlotDetails, PluggableSearchPerson, Podcast, Post, PrePopulatedPost,
+    Picture, Pizza, Plot, PlotDetails, PluggableSearchPerson, Podcast, Post,
-    PrePopulatedPostLargeSlug, PrePopulatedSubPost, Promo, Question, Recipe,
+    PrePopulatedPost, PrePopulatedPostLargeSlug, PrePopulatedSubPost, Promo,
-    Recommendation, Recommender, ReferencedByInline, ReferencedByParent,
+    Question, Recipe, Recommendation, Recommender, ReferencedByGenRel,
-    RelatedPrepopulated, Report, Reservation, Restaurant,
+    ReferencedByInline, ReferencedByParent, RelatedPrepopulated, Report,
-    RowLevelChangePermissionModel, Section, ShortMessage, Simple, Sketch,
+    Reservation, Restaurant, RowLevelChangePermissionModel, Section,
-    State, Story, StumpJoke, Subscriber, SuperVillain, Telegram, Thing,
+    ShortMessage, Simple, Sketch, State, Story, StumpJoke, Subscriber,
-    Topping, UnchangeableObject, UndeletableObject, UnorderedObject,
+    SuperVillain, Telegram, Thing, Topping, UnchangeableObject,
-    UserMessenger, Villain, Vodcast, Whatsit, Widget, Worker, WorkHour,
+    UndeletableObject, UnorderedObject, UserMessenger, Villain, Vodcast,
+    Whatsit, Widget, Worker, WorkHour,
 )
 
 
@@ -944,6 +945,8 @@ site.register(ReferencedByParent)
 site.register(ChildOfReferer)
 site.register(ReferencedByInline)
 site.register(InlineReferer, InlineRefererAdmin)
+site.register(ReferencedByGenRel)
+site.register(GenRelReference)
 
 # We intentionally register Promo and ChapterXtra1 but not Chapter nor ChapterXtra2.
 # That way we cover all four cases:

tests/admin_views/models.py

@@ -938,3 +938,14 @@ class ExplicitlyProvidedPK(models.Model):
 
 class ImplicitlyGeneratedPK(models.Model):
     name = models.IntegerField(unique=True)
+
+
+# Models for #25622
+class ReferencedByGenRel(models.Model):
+    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
+    object_id = models.PositiveIntegerField()
+    content_object = GenericForeignKey('content_type', 'object_id')
+
+
+class GenRelReference(models.Model):
+    references = GenericRelation(ReferencedByGenRel)

tests/admin_views/tests.py

@@ -725,6 +725,14 @@ class AdminViewBasicTest(AdminViewBasicTestCase):
         response = self.client.get(reverse('admin:admin_views_referencedbyinline_changelist'), {TO_FIELD_VAR: 'name'})
         self.assertEqual(response.status_code, 200)
 
+        # #25622 - Specifying a field of a model only referred by a generic
+        # relation should raise DisallowedModelAdminToField.
+        url = reverse('admin:admin_views_referencedbygenrel_changelist')
+        with patch_logger('django.security.DisallowedModelAdminToField', 'error') as calls:
+            response = self.client.get(url, {TO_FIELD_VAR: 'object_id'})
+            self.assertEqual(response.status_code, 400)
+            self.assertEqual(len(calls), 1)
+
         # We also want to prevent the add, change, and delete views from
         # leaking a disallowed field value.
         with patch_logger('django.security.DisallowedModelAdminToField', 'error') as calls: