change_subdomain: Create a deactivated realm on updating subdomain.

When changing the subdomain of a realm, create a deactivated realm with
the old subdomain of the realm, and set its deactivated_redirect to the
new subdomain.
Doing this will help us to do the following:
- When a user visits the old subdomain of a realm, we can tell the user
that the realm has been moved.
- During the registration process, we can assure that the old subdomain
of the realm is not used to create a new realm.

If the subdomain is changed multiple times, the deactivated_redirect
fields of all the deactivated realms are updated to point to the new
uri.

analytics/tests/test_views.py

@@ -745,7 +745,8 @@ class TestSupportEndpoint(ZulipTestCase):
         realm_id = lear_realm.id
         lear_realm = get_realm('new-name')
         self.assertEqual(lear_realm.id, realm_id)
-        self.assertFalse(Realm.objects.filter(string_id='lear').exists())
+        self.assertTrue(Realm.objects.filter(string_id='lear').exists())
+        self.assertTrue(Realm.objects.filter(string_id='lear')[0].deactivated)
 
         result = self.client_post("/activity/support", {"realm_id": f"{lear_realm.id}", "new_subdomain": "new-name"})
         self.assert_in_success_response(["Subdomain unavailable. Please choose a different one."], result)
@@ -753,6 +754,9 @@ class TestSupportEndpoint(ZulipTestCase):
         result = self.client_post("/activity/support", {"realm_id": f"{lear_realm.id}", "new_subdomain": "zulip"})
         self.assert_in_success_response(["Subdomain unavailable. Please choose a different one."], result)
 
+        result = self.client_post("/activity/support", {"realm_id": f"{lear_realm.id}", "new_subdomain": "lear"})
+        self.assert_in_success_response(["Subdomain unavailable. Please choose a different one."], result)
+
     def test_downgrade_realm(self) -> None:
         cordelia = self.example_user('cordelia')
         self.login_user(cordelia)

zerver/lib/actions.py

@@ -856,9 +856,26 @@ def do_reactivate_realm(realm: Realm) -> None:
         }).decode())
 
 def do_change_realm_subdomain(realm: Realm, new_subdomain: str) -> None:
+    old_subdomain = realm.subdomain
+    old_uri = realm.uri
     realm.string_id = new_subdomain
     realm.save(update_fields=["string_id"])
 
+    # If a realm if being renamed multiple times, we should find all the placeholder
+    # realms and reset their deactivated_redirect field to point to the new realm uri
+    placeholder_realms = Realm.objects.filter(deactivated_redirect=old_uri,
+                                              deactivated=True)
+    for placeholder_realm in placeholder_realms:
+        do_add_deactivated_redirect(placeholder_realm, realm.uri)
+
+    # When we change a realm's subdomain the realm with old subdomain is basically
+    # deactivated. We are creating a deactivated realm using old subdomain and setting
+    # it's deactivated redirect to new_subdomain so that we can tell the users that
+    # the realm has been moved to a new subdomain.
+    placeholder_realm = do_create_realm(old_subdomain, "placeholder-realm")
+    do_deactivate_realm(placeholder_realm)
+    do_add_deactivated_redirect(placeholder_realm, realm.uri)
+
 def do_add_deactivated_redirect(realm: Realm, redirect_url: str) -> None:
     realm.deactivated_redirect = redirect_url
     realm.save(update_fields=["deactivated_redirect"])

zerver/tests/test_realm.py

@@ -184,9 +184,10 @@ class RealmTest(ZulipTestCase):
         do_change_realm_subdomain(realm, "newzulip")
         user = get_user_profile_by_email('hamlet@zulip.com')
         self.assertEqual(user.realm.string_id, "newzulip")
-        # This doesn't use a cache right now, but may later.
-        with self.assertRaises(Realm.DoesNotExist):
-            get_realm("zulip")
+
+        placeholder_realm = get_realm("zulip")
+        self.assertTrue(placeholder_realm.deactivated)
+        self.assertEqual(placeholder_realm.deactivated_redirect, user.realm.uri)
 
     def test_do_deactivate_realm_clears_scheduled_jobs(self) -> None:
         user = self.example_user('hamlet')

zerver/tests/test_signup.py

@@ -35,6 +35,7 @@ from zerver.lib.actions import (
     add_new_user_history,
     do_add_default_stream,
     do_change_full_name,
+    do_change_realm_subdomain,
     do_change_user_role,
     do_create_default_stream_group,
     do_create_realm,
@@ -182,6 +183,25 @@ class DeactivationNoticeTestCase(ZulipTestCase):
         result = self.client_get('/accounts/deactivated/')
         self.assertIn('It has moved to <a href="http://example.zulipchat.com">http://example.zulipchat.com</a>.', result.content.decode())
 
+    def test_deactivation_notice_when_realm_subdomain_is_changed(self) -> None:
+        realm = get_realm("zulip")
+        do_change_realm_subdomain(realm, "new-subdomain-name")
+
+        result = self.client_get('/accounts/deactivated/')
+        self.assertIn('It has moved to <a href="http://new-subdomain-name.testserver">http://new-subdomain-name.testserver</a>.', result.content.decode())
+
+    def test_deactivated_redirect_field_of_placeholder_realms_are_modified_on_changing_subdomain_multiple_times(self) -> None:
+        realm = get_realm('zulip')
+        do_change_realm_subdomain(realm, 'new-name-1')
+
+        result = self.client_get('/accounts/deactivated/')
+        self.assertIn('It has moved to <a href="http://new-name-1.testserver">http://new-name-1.testserver</a>.', result.content.decode())
+
+        realm = get_realm('new-name-1')
+        do_change_realm_subdomain(realm, 'new-name-2')
+        result = self.client_get('/accounts/deactivated/')
+        self.assertIn('It has moved to <a href="http://new-name-2.testserver">http://new-name-2.testserver</a>.', result.content.decode())
+
 class AddNewUserHistoryTest(ZulipTestCase):
     def test_add_new_user_history_race(self) -> None:
         """Sends a message during user creation"""
@@ -2523,6 +2543,24 @@ class RealmCreationTest(ZulipTestCase):
         self.assertEqual(result.status_code, 302)
         self.assertTrue(result.url.startswith('http://a-0.testserver/accounts/login/subdomain/'))
 
+    @override_settings(OPEN_REALM_CREATION=True)
+    def test_create_realm_using_old_subdomain_of_a_realm(self) -> None:
+        realm = get_realm("zulip")
+        do_change_realm_subdomain(realm, "new-name")
+
+        password = "test"
+        email = "user1@test.com"
+        realm_name = "Test"
+
+        result = self.client_post('/new/', {'email': email})
+        self.client_get(result["Location"])
+        confirmation_url = self.get_confirmation_url_from_outbox(email)
+        self.client_get(confirmation_url)
+        result = self.submit_reg_form_for_user(email, password,
+                                               realm_subdomain = "zulip",
+                                               realm_name = realm_name)
+        self.assert_in_response("Subdomain unavailable. Please choose a different one.", result)
+
     @override_settings(OPEN_REALM_CREATION=True)
     def test_subdomain_restrictions_root_domain(self) -> None:
         password = "test"