fix: page url is None for headless sites

wagtail/models/__init__.py

@@ -2103,7 +2103,15 @@ class Page(AbstractPage, index.Indexed, ClusterableModel, metaclass=PageBase):
                     "wagtail_serve", args=(self.url_path[len(root_path) :],)
                 )
         except NoReverseMatch:
-            return (site_id, None, None)
+            """
+            wagtail_serve is not mounted, this is most likely a headless Wagtail,
+            use the path rather than processsing through wagtail_serve -1 maintains
+            the leading slash needed to create a root relative URL Path.
+
+            TODO: review whether additional work is needed to support Multisite and i18n
+            url generation in headless Wagtail.
+            """
+            page_path = self.url_path[len(root_path) - 1 :]
 
         # Remove the trailing slash from the URL reverse generates if
         # WAGTAIL_APPEND_SLASH is False and we're not trying to serve

wagtail/tests/test_page_model.py

@@ -432,16 +432,20 @@ class TestRouting(TestCase):
         # for now headless installations will return the url relative to the default site.
         # additional work probably needs to be done to enable multisite in headless modes
         # without this page links in richtext blocks have href=None
-        self.assertEqual(homepage.get_url_parts(), (default_site.id, "http://localhost", "/"))
+        self.assertEqual(
+            homepage.get_url_parts(), (default_site.id, "http://localhost", "/")
+        )
         self.assertEqual(homepage.full_url, "http://localhost/")
         self.assertEqual(homepage.url, "/")
 
         events_page = Page.objects.get(url_path="/home/events/")
-        self.assertEqual(events_page.get_url_parts(), (default_site.id, "http://localhost", "/events/"))
+        self.assertEqual(
+            events_page.get_url_parts(),
+            (default_site.id, "http://localhost", "/events/"),
+        )
         self.assertEqual(events_page.full_url, "http://localhost/events/")
         self.assertEqual(events_page.url, "/events/")
 
-
     def test_request_routing(self):
         homepage = Page.objects.get(url_path="/home/")
         christmas_page = EventPage.objects.get(url_path="/home/events/christmas/")