Add missing bind_to call to PreviewOnEdit

Added test for page preview with custom edit handlers
fixes #7537

CHANGELOG.txt

@@ -46,6 +46,7 @@ Changelog
  * Fix: Page history now works correctly when it contains changes by a deleted user (Dan Braghis)
  * Fix: Add `gettext_lazy` to `ModelAdmin` built in view titles so that language settings are correctly used (Matt Westcott)
  * Fix: Tabbing and keyboard interaction on the Wagtail userbar now aligns with ARIA best practices (Storm Heg)
+ * Fix: Add full support for custom `edit_handler` usage by adding missing `bind_to` call to `PreviewOnEdit` view (Stefan Hammer)
 
 
 2.14.1 (12.08.2021)

docs/releases/2.15.rst

@@ -61,6 +61,7 @@ Bug fixes
  * Page history now works correctly when it contains changes by a deleted user (Dan Braghis)
  * Add ``gettext_lazy`` to ``ModelAdmin`` built in view titles so that language settings are correctly used (Matt Westcott)
  * Tabbing and keyboard interaction on the Wagtail userbar now aligns with ARIA best practices (Storm Heg)
+ * Add full support for custom ``edit_handler`` usage by adding missing ``bind_to`` call to ``PreviewOnEdit`` view (Stefan Hammer)
 
 Upgrade considerations
 ======================

wagtail/admin/tests/pages/test_preview.py

@@ -1,13 +1,17 @@
 import datetime
 
+from functools import wraps
+from unittest import mock
+
 from django.test import TestCase
 from django.urls import reverse
 from django.utils import timezone
 from freezegun import freeze_time
 
+from wagtail.admin.edit_handlers import FieldPanel, ObjectList, TabbedInterface
 from wagtail.admin.views.pages.preview import PreviewOnEdit
 from wagtail.core.models import Page
-from wagtail.tests.testapp.models import EventCategory, SimplePage, StreamPage
+from wagtail.tests.testapp.models import EventCategory, EventPage, SimplePage, StreamPage
 from wagtail.tests.utils import WagtailTestUtils
 
 
@@ -57,6 +61,21 @@ class TestIssue2599(TestCase, WagtailTestUtils):
         self.assertEqual(response.context['self'].get_parent(), homepage)
 
 
+def clear_edit_handler(page_cls):
+    def decorator(fn):
+        @wraps(fn)
+        def decorated(*args, **kwargs):
+            # Clear any old EditHandlers generated
+            page_cls.get_edit_handler.cache_clear()
+            try:
+                fn(*args, **kwargs)
+            finally:
+                # Clear the bad EditHandler generated just now
+                page_cls.get_edit_handler.cache_clear()
+        return decorated
+    return decorator
+
+
 class TestPreview(TestCase, WagtailTestUtils):
     fixtures = ['test.json']
 
@@ -174,6 +193,83 @@ class TestPreview(TestCase, WagtailTestUtils):
             response = self.client.get(preview_url)
             self.assertEqual(response.status_code, 200)
 
+    @clear_edit_handler(EventPage)
+    def test_preview_with_custom_edit_handler(self):
+        """
+        The test is based on TestPreview.test_preview_on_create_with_m2m_field, except that the "categories"
+        FieldPanel is only visible to superusers. Non-superusers should not be able to set "categories" for
+        the preview.
+        """
+
+        class SuperuserEventCategoriesObjectList(ObjectList):
+            def on_request_bound(self):
+                new_children = []
+                for child in self.children:
+                    # skip the "categories" FieldPanel for non-superusers
+                    if isinstance(child, FieldPanel) and child.field_name == "categories" and not self.request.user.is_superuser:
+                        continue
+
+                    new_child = child.bind_to(
+                        model=self.model,
+                        instance=self.instance,
+                        request=self.request,
+                        form=self.form,
+                    )
+                    new_children.append(new_child)
+                self.children = new_children
+
+        new_tabbed_interface = TabbedInterface([
+            SuperuserEventCategoriesObjectList(EventPage.content_panels),
+            ObjectList(EventPage.promote_panels),
+        ])
+
+        with mock.patch.object(EventPage, 'edit_handler', new=new_tabbed_interface, create=True):
+            # Non-superusers should not see categories panel, so even though "post_data" contains "categories",
+            # it should not be considered for the preview request.
+            self.login(username='siteeditor', password='password')
+
+            preview_url = reverse('wagtailadmin_pages:preview_on_add',
+                                  args=('tests', 'eventpage', self.home_page.id))
+            response = self.client.post(preview_url, self.post_data)
+
+            # Check the JSON response
+            self.assertEqual(response.status_code, 200)
+            self.assertJSONEqual(response.content.decode(), {'is_valid': True})
+
+            # Check the user can refresh the preview
+            preview_session_key = 'wagtail-preview-tests-eventpage-{}'.format(self.home_page.id)
+            self.assertTrue(preview_session_key in self.client.session)
+
+            response = self.client.get(preview_url)
+
+            # Check the HTML response
+            self.assertEqual(response.status_code, 200)
+            self.assertTemplateUsed(response, 'tests/event_page.html')
+            self.assertContains(response, "Beach party")
+            self.assertNotContains(response, "<li>Parties</li>")
+            self.assertNotContains(response, "<li>Holidays</li>")
+
+            # Since superusers see the "categories" panel, the posted data should be used for the preview.
+            self.login(username='superuser', password='password')
+            response = self.client.post(preview_url, self.post_data)
+
+            # Check the JSON response
+            self.assertEqual(response.status_code, 200)
+            self.assertJSONEqual(response.content.decode(), {'is_valid': True})
+
+            # Check the user can refresh the preview
+            preview_session_key = 'wagtail-preview-tests-eventpage-{}'.format(self.home_page.id)
+            self.assertTrue(preview_session_key in self.client.session)
+
+            response = self.client.get(preview_url)
+
+            # Check the HTML response
+            self.assertEqual(response.status_code, 200)
+            self.assertTemplateUsed(response, 'tests/event_page.html')
+            self.assertContains(response, "Beach party")
+            self.assertContains(response, "<li>Parties</li>")
+            self.assertContains(response, "<li>Holidays</li>")
+
 
 class TestDisablePreviewButton(TestCase, WagtailTestUtils):
     """

wagtail/admin/views/pages/preview.py

@@ -48,7 +48,7 @@ class PreviewOnEdit(View):
                                  id=self.kwargs["page_id"]).get_latest_revision_as_page()
 
     def get_form(self, page, query_dict):
-        form_class = page.get_edit_handler().get_form_class()
+        form_class = page.get_edit_handler().bind_to(instance=page, request=self.request).get_form_class()
         parent_page = page.get_parent().specific
 
         if self.session_key not in self.request.session: