slack import: Be less strict in `check_subdomain_available`.

If the sysadmin is doing something explicit in a management command,
it's OK to take a reserved or short subdomain.

Fixes #9166.

zerver/forms.py

@@ -55,7 +55,7 @@ def email_is_not_mit_mailing_list(email: Text) -> None:
             else:
                 raise AssertionError("Unexpected DNS error")
 
-def check_subdomain_available(subdomain: str) -> None:
+def check_subdomain_available(subdomain: str, from_management_command: bool=False) -> None:
     error_strings = {
         'too short': _("Subdomain needs to have length 3 or greater."),
         'extremal dash': _("Subdomain cannot start or end with a '-'."),
@@ -70,6 +70,8 @@ def check_subdomain_available(subdomain: str) -> None:
         raise ValidationError(error_strings['extremal dash'])
     if not re.match('^[a-z0-9-]*$', subdomain):
         raise ValidationError(error_strings['bad character'])
+    if from_management_command:
+        return
     if len(subdomain) < 3:
         raise ValidationError(error_strings['too short'])
     if is_reserved_subdomain(subdomain) or \

zerver/management/commands/import.py

@@ -74,7 +74,7 @@ import a database dump from one or more JSON files."""
             for model in models_to_import:
                 self.new_instance_check(model)
 
-        check_subdomain_available(subdomain)
+        check_subdomain_available(subdomain, from_management_command=True)
 
         for path in options['export_files']:
             if not os.path.exists(path):

zerver/tests/test_signup.py

@@ -6,6 +6,7 @@ from django.contrib.sites.models import Site
 from django.http import HttpResponse
 from django.test import TestCase, override_settings
 from django.utils.timezone import now as timezone_now
+from django.core.exceptions import ValidationError
 
 from mock import patch, MagicMock
 from zerver.lib.test_helpers import MockLDAP
@@ -14,7 +15,7 @@ from confirmation.models import Confirmation, create_confirmation_link, Multiuse
     generate_key, confirmation_url, get_object_from_key, ConfirmationKeyException
 from confirmation import settings as confirmation_settings
 
-from zerver.forms import HomepageForm, WRONG_SUBDOMAIN_ERROR
+from zerver.forms import HomepageForm, WRONG_SUBDOMAIN_ERROR, check_subdomain_available
 from zerver.lib.actions import do_change_password
 from zerver.views.auth import login_or_register_remote_user, \
     redirect_and_log_into_subdomain
@@ -1521,6 +1522,15 @@ class RealmCreationTest(ZulipTestCase):
         self.assert_in_success_response(["available"], result)
         self.assert_not_in_success_response(["unavailable"], result)
 
+    def test_subdomain_check_management_command(self) -> None:
+        # Short names should work
+        check_subdomain_available('aa', from_management_command=True)
+        # So should reserved ones
+        check_subdomain_available('zulip', from_management_command=True)
+        # malformed names should still not
+        with self.assertRaises(ValidationError):
+            check_subdomain_available('-ba_d-', from_management_command=True)
+
 class UserSignUpTest(ZulipTestCase):
 
     def _assert_redirected_to(self, result: HttpResponse, url: Text) -> None: