validators: Add check_int_in validator.

This is a useful helper for our enum format fields where we want to
only allow a fixed list of integer values.

zerver/lib/validator.py

@@ -30,7 +30,7 @@ import ujson
 from django.utils.translation import ugettext as _
 from django.core.exceptions import ValidationError
 from django.core.validators import validate_email, URLValidator
-from typing import Iterable, Optional, Tuple, cast
+from typing import Iterable, Optional, Tuple, cast, List
 
 from datetime import datetime
 from zerver.lib.request import JsonableError
@@ -92,6 +92,17 @@ def check_int(var_name: str, val: object) -> Optional[str]:
         return _('%s is not an integer') % (var_name,)
     return None
 
+def check_int_in(possible_values: List[int]) -> Validator:
+    def validator(var_name: str, val: object) -> Optional[str]:
+        not_int = check_int(var_name, val)
+        if not_int is not None:
+            return not_int
+        if val not in possible_values:
+            return _("Invalid %s") % (var_name,)
+        return None
+
+    return validator
+
 def check_float(var_name: str, val: object) -> Optional[str]:
     if not isinstance(val, float):
         return _('%s is not a float') % (var_name,)

zerver/tests/test_decorators.py

@@ -45,7 +45,7 @@ from zerver.lib.validator import (
     check_string, check_dict, check_dict_only, check_bool, check_float, check_int, check_list, Validator,
     check_variable_type, equals, check_none_or, check_url, check_short_string,
     check_string_fixed_length, check_capped_string, check_color, to_non_negative_int,
-    check_string_or_int_list, check_string_or_int
+    check_string_or_int_list, check_string_or_int, check_int_in
 )
 from zerver.models import \
     get_realm, get_user, UserProfile, Realm
@@ -758,6 +758,11 @@ class ValidatorTestCase(TestCase):
         x = "hi"
         self.assertEqual(check_capped_string(5)('x', x), None)
 
+    def test_check_int_in(self) -> None:
+        self.assertEqual(check_int_in([1])("Test", 1), None)
+        self.assertEqual(check_int_in([1])("Test", 2), "Invalid Test")
+        self.assertEqual(check_int_in([1])("Test", "t"), "Test is not an integer")
+
     def test_check_short_string(self) -> None:
         x = "hello"  # type: Any
         self.assertEqual(check_short_string('x', x), None)