Fix queryset ordering and add a test to confirm ordering matches expectation in all setups

CHANGELOG.txt

@@ -19,6 +19,7 @@ Changelog
  * Fix: Handle all exceptions from `Image.get_file_size` (Andrew Plummer)
  * Fix: Fix display of breadcrumbs in ModelAdmin (LB (Ben Johnston))
  * Fix: Remove duplicate border radius of avatars (Benjamin Thurm)
+ * Fix: Site.get_site_root_paths() preferring other sites over the default when some sites share the same root_page (Andy Babic)
 
 
 2.1 (22.05.2018)

docs/releases/2.2.rst

@@ -32,6 +32,7 @@ Bug fixes
  * Handle all exceptions from ``Image.get_file_size`` (Andrew Plummer)
  * Fix display of breadcrumbs in ModelAdmin (LB (Ben Johnston))
  * Remove duplicate border radius of avatars (Benjamin Thurm)
+ * Site.get_site_root_paths() preferring other sites over the default when some sites share the same root_page (Andy Babic)
 
 Upgrade considerations
 ======================

wagtail/core/models.py

@@ -161,7 +161,7 @@ class Site(models.Model):
             result = [
                 (site.id, site.root_page.url_path, site.root_url)
                 for site in Site.objects.select_related('root_page').order_by(
-                    '-root_page__url_path', 'is_default_site', 'hostname')
+                    '-root_page__url_path', '-is_default_site', 'hostname')
             ]
             cache.set('wagtail_site_root_paths', result, 3600)
 

wagtail/core/tests/test_sites.py

@@ -122,3 +122,30 @@ class TestDefaultSite(TestCase):
         with self.assertRaises(Site.MultipleObjectsReturned):
             # If there already are multiple default sites, you're in trouble
             site.clean_fields()
+
+
+class TestGetSiteRootPaths(TestCase):
+
+    def setUp(self):
+        self.default_site = Site.objects.get()
+        self.abc_site = Site.objects.create(
+            hostname='abc.com', root_page=self.default_site.root_page
+        )
+        self.def_site = Site.objects.create(
+            hostname='def.com', root_page=self.default_site.root_page
+        )
+
+        # Changing the hostname to show that being the default site takes
+        # promotes a site over the alphabetical ordering of hostname
+        self.default_site.hostname = 'xyz.com'
+        self.default_site.save()
+
+    def test_result_order_when_multiple_sites_share_the_same_root_page(self):
+        result = Site.get_site_root_paths()
+
+        # An entry for the default site should come first
+        self.assertEqual(result[0][0], self.default_site.id)
+
+        # Followed by entries for others in 'host' alphabetical order
+        self.assertEqual(result[1][0], self.abc_site.id)
+        self.assertEqual(result[2][0], self.def_site.id)