Added error message for settings when site not defined (#4362)

* Added error message for settings when site not defined

* added tests

* fixed linter error

* implemented feedback

wagtail/contrib/settings/tests/test_admin.py

@@ -127,6 +127,19 @@ class TestSettingEditView(BaseTestSettingView):
         self.assertEqual(setting.title, 'Edited site title')
         self.assertEqual(setting.email, 'test@example.com')
 
+    def test_get_edit_current_site(self):
+        url = reverse('wagtailsettings:edit', args=('tests', 'testsetting'))
+        default_site = Site.objects.get(is_default_site=True)
+
+        response = self.client.get(url)
+        self.assertRedirects(response, status_code=302, expected_url='%s%s/' % (url, default_site.pk))
+
+    def test_get_edit_current_site_invalid(self):
+        Site.objects.all().delete()
+        url = reverse('wagtailsettings:edit', args=('tests', 'testsetting'))
+        response = self.client.get(url)
+        self.assertRedirects(response, status_code=302, expected_url='/admin/')
+
 
 @override_settings(ALLOWED_HOSTS=['testserver', 'example.com', 'noneoftheabove.example.com'])
 class TestMultiSite(BaseTestSettingView):

wagtail/contrib/settings/views.py

@@ -39,6 +39,9 @@ def edit_current_site(request, app_name, model_name):
     # Redirect the user to the edit page for the current site
     # (or the current request does not correspond to a site, the first site in the list)
     site = request.site or Site.objects.first()
+    if not site:
+        messages.error(request, _("This setting could not be opened because there is no site defined."))
+        return redirect('wagtailadmin_home')
     return redirect('wagtailsettings:edit', app_name, model_name, site.pk)