[1.10.x] Fixed #27302 -- Fixed ModelAdmin.construct_change_message() changed field detection

Thanks Ramiro Morales for the report and Tim Graham for the review.
Backport of 67eee5e4fa08f4404445ebf4f54b686e68a8530c from master.

3 files changed, 45 insertions, 26 deletions

diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index eaf6452707..569bf3b057 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -929,7 +929,6 @@ class ModelAdmin(BaseModelAdmin):
                 return urlencode({'_changelist_filters': preserved_filters})
         return ''
 
-    @translation_override(None)
     def construct_change_message(self, request, form, formsets, add=False):
         """
         Construct a JSON structure describing changes from a changed object.
@@ -943,29 +942,30 @@ class ModelAdmin(BaseModelAdmin):
             change_message.append({'changed': {'fields': form.changed_data}})
 
         if formsets:
-            for formset in formsets:
-                for added_object in formset.new_objects:
-                    change_message.append({
-                        'added': {
-                            'name': force_text(added_object._meta.verbose_name),
-                            'object': force_text(added_object),
-                        }
-                    })
-                for changed_object, changed_fields in formset.changed_objects:
-                    change_message.append({
-                        'changed': {
-                            'name': force_text(changed_object._meta.verbose_name),
-                            'object': force_text(changed_object),
-                            'fields': changed_fields,
-                        }
-                    })
-                for deleted_object in formset.deleted_objects:
-                    change_message.append({
-                        'deleted': {
-                            'name': force_text(deleted_object._meta.verbose_name),
-                            'object': force_text(deleted_object),
-                        }
-                    })
+            with translation_override(None):
+                for formset in formsets:
+                    for added_object in formset.new_objects:
+                        change_message.append({
+                            'added': {
+                                'name': force_text(added_object._meta.verbose_name),
+                                'object': force_text(added_object),
+                            }
+                        })
+                    for changed_object, changed_fields in formset.changed_objects:
+                        change_message.append({
+                            'changed': {
+                                'name': force_text(changed_object._meta.verbose_name),
+                                'object': force_text(changed_object),
+                                'fields': changed_fields,
+                            }
+                        })
+                    for deleted_object in formset.deleted_objects:
+                        change_message.append({
+                            'deleted': {
+                                'name': force_text(deleted_object._meta.verbose_name),
+                                'object': force_text(deleted_object),
+                            }
+                        })
         return change_message
 
     def message_user(self, request, message, level=messages.INFO, extra_tags='',
diff --git a/docs/releases/1.10.2.txt b/docs/releases/1.10.2.txt
index d434a80bba..83c935e7c5 100644
--- a/docs/releases/1.10.2.txt
+++ b/docs/releases/1.10.2.txt
@@ -25,3 +25,6 @@ Bugfixes
 
 * Fixed a crash in ``runserver`` logging during a "Broken pipe" error
   (:ticket:`27271`).
+
+* Fixed a regression where unchanged localized date/time fields were listed as
+  changed in the admin's model history messages (:ticket:`27302`).
diff --git a/tests/admin_utils/test_logentry.py b/tests/admin_utils/test_logentry.py
index 8259bf0cc1..4ea182e2aa 100644
--- a/tests/admin_utils/test_logentry.py
+++ b/tests/admin_utils/test_logentry.py
@@ -25,7 +25,7 @@ class LogEntryTests(TestCase):
         self.a1 = Article.objects.create(
             site=self.site,
             title="Title",
-            created=datetime(2008, 3, 18, 11, 54),
+            created=datetime(2008, 3, 12, 11, 54),
         )
         content_type_pk = ContentType.objects.get_for_model(Article).pk
         LogEntry.objects.log_action(
@@ -51,7 +51,7 @@ class LogEntryTests(TestCase):
         """
         post_data = {
             'site': self.site.pk, 'title': 'Changed', 'hist': 'Some content',
-            'created_0': '2008-03-18', 'created_1': '11:54',
+            'created_0': '2008-03-12', 'created_1': '11:54',
         }
         change_url = reverse('admin:admin_utils_article_change', args=[quote(self.a1.pk)])
         response = self.client.post(change_url, post_data)
@@ -70,6 +70,22 @@ class LogEntryTests(TestCase):
         with translation.override('fr'):
             self.assertEqual(logentry.get_change_message(), 'Ajout.')
 
+    @override_settings(USE_L10N=True)
+    def test_logentry_change_message_localized_datetime_input(self):
+        """
+        Localized date/time inputs shouldn't affect changed form data detection.
+        """
+        post_data = {
+            'site': self.site.pk, 'title': 'Changed', 'hist': 'Some content',
+            'created_0': '12/03/2008', 'created_1': '11:54',
+        }
+        with translation.override('fr'):
+            change_url = reverse('admin:admin_utils_article_change', args=[quote(self.a1.pk)])
+            response = self.client.post(change_url, post_data)
+            self.assertRedirects(response, reverse('admin:admin_utils_article_changelist'))
+        logentry = LogEntry.objects.filter(content_type__model__iexact='article').latest('id')
+        self.assertEqual(logentry.get_change_message(), 'Changed title and hist.')
+
     def test_logentry_change_message_formsets(self):
         """
         All messages for changed formsets are logged in a change message.