Exclude root pages from `ModelAdmin`s (#7213)

Previously, this would fail, as `user_can_copy_obj` doesn't handle root
pages. Root pages also are special in a number of ways, and handling
copying is tricky and non-obvious.

If someone needs to show root pages (for some reason), they'll have to
special case them themselves.

CHANGELOG.txt

@@ -18,6 +18,7 @@ Changelog
  * Fix: Snippet admin urls are now namespaced to avoid ambiguity with the primary key component of the url (Matt Westcott)
  * Fix: Save order of promoted search results (Hardcodd)
  * Fix: Prevent error on copying pages with ClusterTaggableManager relations and multi-level inheritance (Chris Pollard)
+ * Fix: Prevent failure on root page when registering the Page model with ModelAdmin (Jake Howard)
 
 
 2.13.2 (17.06.2021)

CONTRIBUTORS.rst

@@ -518,6 +518,7 @@ Contributors
 * hardcodd
 * Chris Pollard
 * Godswill Melford
+* Jake Howard
 
 Translators
 ===========

docs/releases/2.14.rst

@@ -29,6 +29,7 @@ Bug fixes
  * Prevent “Forgotten password” link from overlapping with field on mobile devices (Helen Chapman)
  * Snippet admin urls are now namespaced to avoid ambiguity with the primary key component of the url (Matt Westcott)
  * Prevent error on copying pages with ClusterTaggableManager relations and multi-level inheritance (Chris Pollard)
+ * Prevent failure on root page when registering the Page model with ModelAdmin (Jake Howard)
 
 Upgrade considerations
 ======================

wagtail/contrib/modeladmin/options.py

@@ -240,6 +240,9 @@ class ModelAdmin(WagtailRegisterable):
         ordering = self.get_ordering(request)
         if ordering:
             qs = qs.order_by(*ordering)
+        if self.is_pagemodel:
+            # If we're listing pages, exclude the root page
+            qs = qs.exclude(depth=1)
         return qs
 
     def get_search_fields(self, request):

wagtail/contrib/modeladmin/tests/test_page_modeladmin.py

@@ -54,6 +54,14 @@ class TestIndexView(TestCase, WagtailTestUtils):
         # There should still be four results
         self.assertEqual(response.context['result_count'], 4)
 
+    def test_using_core_page(self):
+        # The core page is slightly different to other pages, so exclude it
+        response = self.client.get('/admin/wagtailcore/page/')
+        self.assertEqual(response.status_code, 200)
+
+        root_page = Page.objects.get(depth=1)
+        self.assertNotIn(root_page, response.context['paginator'].object_list)
+
 
 class TestExcludeFromExplorer(TestCase, WagtailTestUtils):
     fixtures = ['modeladmintest_test.json']
@@ -188,6 +196,12 @@ class TestEditView(TestCase, WagtailTestUtils):
 
         self.assertEqual(response.status_code, 404)
 
+    def test_using_core_page(self):
+        # The core page is slightly different to other pages, so exclude it
+        root_page = Page.objects.get(depth=1)
+        response = self.client.get('/admin/wagtailcore/page/{}/'.format(root_page.id))
+        self.assertEqual(response.status_code, 404)
+
 
 class TestDeleteView(TestCase, WagtailTestUtils):
     fixtures = ['test_specific.json']

wagtail/tests/modeladmintest/wagtail_hooks.py

@@ -3,6 +3,7 @@ from wagtail.contrib.modeladmin.helpers import WagtailBackendSearchHandler
 from wagtail.contrib.modeladmin.options import (
     ModelAdmin, ModelAdminGroup, ThumbnailMixin, modeladmin_register)
 from wagtail.contrib.modeladmin.views import CreateView, EditView, IndexView
+from wagtail.core.models import Page
 from wagtail.tests.testapp.models import BusinessChild, EventPage, SingleEventPage
 
 from .forms import PublisherModelAdminForm
@@ -171,6 +172,11 @@ class RelatedLinkAdmin(ModelAdmin):
     menu_label = "Related Links"
 
 
+class PageAdmin(ModelAdmin):
+    model = Page
+    menu_label = "Page"
+
+
 modeladmin_register(AuthorModelAdmin)
 modeladmin_register(BookModelAdmin)
 modeladmin_register(TokenModelAdmin)
@@ -182,3 +188,4 @@ modeladmin_register(FriendAdmin)
 modeladmin_register(VisitorAdmin)
 modeladmin_register(ContributorAdmin)
 modeladmin_register(RelatedLinkAdmin)
+modeladmin_register(PageAdmin)