[2.1.x] Fixed #29682 -- Fixed admin change form crash if a view-only model's form has an extra field.

Backport of d311124be5 from master

django/contrib/admin/helpers.py

@@ -167,7 +167,7 @@ class AdminReadonlyField:
         if form._meta.labels and class_name in form._meta.labels:
             label = form._meta.labels[class_name]
         else:
-            label = label_for_field(field, form._meta.model, model_admin)
+            label = label_for_field(field, form._meta.model, model_admin, form=form)
 
         if form._meta.help_texts and class_name in form._meta.help_texts:
             help_text = form._meta.help_texts[class_name]

django/contrib/admin/utils.py

@@ -319,7 +319,7 @@ def _get_non_gfk_field(opts, name):
     return field
 
 
-def label_for_field(name, model, model_admin=None, return_attr=False):
+def label_for_field(name, model, model_admin=None, return_attr=False, form=None):
     """
     Return a sensible label for a field name. The name can be a callable,
     property (but not created with @property decorator), or the name of an
@@ -346,10 +346,14 @@ def label_for_field(name, model, model_admin=None, return_attr=False):
                 attr = getattr(model_admin, name)
             elif hasattr(model, name):
                 attr = getattr(model, name)
+            elif form and name in form.fields:
+                attr = form.fields[name]
             else:
                 message = "Unable to lookup '%s' on %s" % (name, model._meta.object_name)
                 if model_admin:
                     message += " or %s" % (model_admin.__class__.__name__,)
+                if form:
+                    message += " or %s" % form.__class__.__name__
                 raise AttributeError(message)
 
             if hasattr(attr, "short_description"):

docs/releases/2.1.1.txt

@@ -38,3 +38,6 @@ Bugfixes
 
 * Made the admin change view redirect to the changelist view after a POST if
   the user has the 'view' permission (:ticket:`29663`).
+
+* Fixed admin change view crash for view-only users if the form has an extra
+  form field (:ticket:`29682`).

tests/admin_utils/tests.py

@@ -286,6 +286,22 @@ class UtilsTests(SimpleTestCase):
             ("not Really the Model", MockModelAdmin.test_from_model)
         )
 
+    def test_label_for_field_form_argument(self):
+        class ArticleForm(forms.ModelForm):
+            extra_form_field = forms.BooleanField()
+
+            class Meta:
+                fields = '__all__'
+                model = Article
+
+        self.assertEqual(
+            label_for_field('extra_form_field', Article, form=ArticleForm()),
+            'Extra form field'
+        )
+        msg = "Unable to lookup 'nonexistent' on Article or ArticleForm"
+        with self.assertRaisesMessage(AttributeError, msg):
+            label_for_field('nonexistent', Article, form=ArticleForm()),
+
     def test_label_for_property(self):
         # NOTE: cannot use @property decorator, because of
         # AttributeError: 'property' object has no attribute 'short_description'

tests/admin_views/admin.py

@@ -91,6 +91,14 @@ class ChapterXtra1Admin(admin.ModelAdmin):
     )
 
 
+class ArticleForm(forms.ModelForm):
+    extra_form_field = forms.BooleanField(required=False)
+
+    class Meta:
+        fields = '__all__'
+        model = Article
+
+
 class ArticleAdmin(admin.ModelAdmin):
     list_display = (
         'content', 'date', callable_year, 'model_year', 'modeladmin_year',
@@ -101,10 +109,11 @@ class ArticleAdmin(admin.ModelAdmin):
     list_filter = ('date', 'section')
     autocomplete_fields = ('section',)
     view_on_site = False
+    form = ArticleForm
     fieldsets = (
         ('Some fields', {
             'classes': ('collapse',),
-            'fields': ('title', 'content')
+            'fields': ('title', 'content', 'extra_form_field'),
         }),
         ('Some other fields', {
             'classes': ('wide',),

tests/admin_views/tests.py

@@ -1768,6 +1768,7 @@ class AdminViewPermissionsTest(TestCase):
         response = self.client.get(article_change_url)
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.context['title'], 'View article')
+        self.assertContains(response, '<label>Extra form field:</label>')
         self.assertContains(response, '<a href="/test_admin/admin/admin_views/article/" class="closelink">Close</a>')
         post = self.client.post(article_change_url, change_dict)
         self.assertEqual(post.status_code, 302)