validators: Add optional keys feature to check_dict and check_dict_only.

along with the `required_keys` argument an additional `optional_keys`
argument can be passed to both `check_dict` and `check_dict_only`.
Fixes zulip#10892.

Author: Hypro999

zerver/lib/validator.py

@@ -140,6 +140,7 @@ def f(var_name: str, val: object) -> Optional[str]:
     return f
 
 def check_dict(required_keys: Iterable[Tuple[str, Validator]]=[],
+               optional_keys: Iterable[Tuple[str, Validator]]=[],
                value_validator: Optional[Validator]=None,
                _allow_only_listed_keys: bool=False) -> Validator:
     def f(var_name: str, val: object) -> Optional[str]:
@@ -155,6 +156,13 @@ def f(var_name: str, val: object) -> Optional[str]:
             if error:
                 return error
 
+        for k, sub_validator in optional_keys:
+            if k in val:
+                vname = '%s["%s"]' % (var_name, k)
+                error = sub_validator(vname, val[k])
+                if error:
+                    return error
+
         if value_validator:
             for key in val:
                 vname = '%s contains a value that' % (var_name,)
@@ -163,16 +171,19 @@ def f(var_name: str, val: object) -> Optional[str]:
                     return error
 
         if _allow_only_listed_keys:
-            delta_keys = set(val.keys()) - set(x[0] for x in required_keys)
+            required_keys_set = set(x[0] for x in required_keys)
+            optional_keys_set = set(x[0] for x in optional_keys)
+            delta_keys = set(val.keys()) - required_keys_set - optional_keys_set
             if len(delta_keys) != 0:
                 return _("Unexpected arguments: %s" % (", ".join(list(delta_keys))))
 
         return None
 
     return f
 
-def check_dict_only(required_keys: Iterable[Tuple[str, Validator]]) -> Validator:
-    return check_dict(required_keys, _allow_only_listed_keys=True)
+def check_dict_only(required_keys: Iterable[Tuple[str, Validator]],
+                    optional_keys: Iterable[Tuple[str, Validator]]=[]) -> Validator:
+    return check_dict(required_keys, optional_keys, _allow_only_listed_keys=True)
 
 def check_variable_type(allowed_type_funcs: Iterable[Validator]) -> Validator:
     """

zerver/tests/test_decorators.py

@@ -861,6 +861,35 @@ def test_check_dict(self) -> None:
         error = check_dict_only(keys)('x', x)
         self.assertEqual(error, 'Unexpected arguments: state')
 
+        # Test optional keys
+        optional_keys = [
+            ('food', check_list(check_string)),
+            ('year', check_int)
+        ]
+
+        x = {
+            'names': ['alice', 'bob'],
+            'city': 'Boston',
+            'food': ['Lobster Spaghetti']
+        }
+
+        error = check_dict(keys)('x', x)
+        self.assertEqual(error, None)  # since _allow_only_listed_keys is False
+
+        error = check_dict_only(keys)('x', x)
+        self.assertEqual(error, 'Unexpected arguments: food')
+
+        error = check_dict_only(keys, optional_keys)('x', x)
+        self.assertEqual(error, None)
+
+        x = {
+            'names': ['alice', 'bob'],
+            'city': 'Boston',
+            'food': 'Lobster Spaghetti'
+        }
+        error = check_dict_only(keys, optional_keys)('x', x)
+        self.assertEqual(error, 'x["food"] is not a list')
+
     def test_encapsulation(self) -> None:
         # There might be situations where we want deep
         # validation, but the error message should be customized.