From 443503d1450e628de24943822799a34b1c3ee92c Mon Sep 17 00:00:00 2001
From: Matt Westcott <matt@west.co.tt>
Date: Thu, 12 Apr 2018 17:23:13 +0100
Subject: [PATCH] Fix non-model form fields being compared. Fixes #3737

---
 wagtail/admin/edit_handlers.py          |  5 +-
 wagtail/admin/tests/test_pages_views.py | 69 ++++++++++++++++++++++++-
 2 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/wagtail/admin/edit_handlers.py b/wagtail/admin/edit_handlers.py
index a28d21c38a..b152ed193f 100644
--- a/wagtail/admin/edit_handlers.py
+++ b/wagtail/admin/edit_handlers.py
@@ -508,7 +508,10 @@ class FieldPanel(EditHandler):
         comparator_class = self.get_comparison_class()
 
         if comparator_class:
-            return [curry(comparator_class, self.db_field)]
+            try:
+                return [curry(comparator_class, self.db_field)]
+            except FieldDoesNotExist:
+                return []
         return []
 
     @cached_property
diff --git a/wagtail/admin/tests/test_pages_views.py b/wagtail/admin/tests/test_pages_views.py
index 5699038fb0..4ff87af403 100644
--- a/wagtail/admin/tests/test_pages_views.py
+++ b/wagtail/admin/tests/test_pages_views.py
@@ -27,8 +27,8 @@ from wagtail.search.index import SearchField
 from wagtail.tests.testapp.models import (
     EVENT_AUDIENCE_CHOICES, Advert, AdvertPlacement, BusinessChild, BusinessIndex, BusinessSubIndex,
     DefaultStreamPage, EventCategory, EventPage, EventPageCarouselItem, FilePage,
-    ManyToManyBlogPage, SimplePage, SingleEventPage, SingletonPage, StandardChild, StandardIndex,
-    TaggedPage)
+    FormClassAdditionalFieldPage, ManyToManyBlogPage, SimplePage, SingleEventPage, SingletonPage,
+    StandardChild, StandardIndex, TaggedPage)
 from wagtail.tests.utils import WagtailTestUtils
 from wagtail.users.models import UserProfile
 
@@ -4052,6 +4052,71 @@ class TestCompareRevisions(TestCase, WagtailTestUtils):
         self.assertContains(response, '<span class="deletion">Last Christmas I gave you my heart, but the very next day you gave it away</span><span class="addition">This year, to save me from tears, I&#39;ll just feed it to the dog</span>')
 
 
+class TestCompareRevisionsWithNonModelField(TestCase, WagtailTestUtils):
+    """
+    Tests if form fields defined in the base_form_class will not be included.
+    in revisions view as they are not actually on the model.
+    Flagged in issue #3737
+    Note: Actual tests for comparison classes can be found in test_compare.py
+    """
+
+    fixtures = ['test.json']
+    # FormClassAdditionalFieldPage
+
+    def setUp(self):
+        # Find root page
+        self.root_page = Page.objects.get(id=2)
+
+        # Add child page of class with base_form_class override
+        # non model field is 'code'
+        self.test_page = FormClassAdditionalFieldPage(
+            title='A Statement',
+            slug='a-statement',
+            location='Early Morning Cafe, Mainland, NZ',
+            body="<p>hello</p>"
+        )
+        self.root_page.add_child(instance=self.test_page)
+
+        # add new revision
+        self.test_page.title = 'Statement'
+        self.test_page.location = 'Victory Monument, Bangkok'
+        self.test_page.body = (
+            "<p>I would like very much to go into the forrest.</p>"
+        )
+        self.test_page_revision = self.test_page.save_revision()
+        self.test_page_revision.created_at = local_datetime(2017, 10, 15)
+        self.test_page_revision.save()
+
+        # add another new revision
+        self.test_page.title = 'True Statement'
+        self.test_page.location = 'Victory Monument, Bangkok'
+        self.test_page.body = (
+            "<p>I would like very much to go into the forest.</p>"
+        )
+        self.test_page_revision_new = self.test_page.save_revision()
+        self.test_page_revision_new.created_at = local_datetime(2017, 10, 16)
+        self.test_page_revision_new.save()
+
+        self.login()
+
+    def test_base_form_class_used(self):
+        """First ensure that the non-model field is appearing in edit."""
+        edit_url = reverse('wagtailadmin_pages:add', args=('tests', 'formclassadditionalfieldpage', self.test_page.id))
+        response = self.client.get(edit_url)
+        self.assertContains(response, '<input type="text" name="code" required id="id_code" maxlength="5" />', html=True)
+
+    def test_compare_revisions(self):
+        """Confirm that the non-model field is not shown in revision."""
+        compare_url = reverse(
+            'wagtailadmin_pages:revisions_compare',
+            args=(self.test_page.id, self.test_page_revision.id, self.test_page_revision_new.id)
+        )
+        response = self.client.get(compare_url)
+        self.assertContains(response, '<span class="deletion">forrest.</span><span class="addition">forest.</span>')
+        # should not contain the field defined in the formclass used
+        self.assertNotContains(response, '<h2>Code:</h2>')
+
+
 class TestRevisionsUnschedule(TestCase, WagtailTestUtils):
     fixtures = ['test.json']