Allow any subtype of typing.Mapping[str, Any] to be passed in as kwargs.

mypy/checkexpr.py

@@ -957,7 +957,8 @@ def check_argument_types(self, arg_types: List[Type], arg_kinds: List[int],
                     messages.invalid_var_arg(arg_type, context)
                 if (arg_kinds[actual] == nodes.ARG_STAR2 and
                         not self.is_valid_keyword_var_arg(arg_type)):
-                    messages.invalid_keyword_var_arg(arg_type, context)
+                    is_mapping = is_subtype(arg_type, self.chk.named_type('typing.Mapping'))
+                    messages.invalid_keyword_var_arg(arg_type, is_mapping, context)
                 # Get the type of an individual actual argument (for *args
                 # and **args this is the item type, not the collection type).
                 if (isinstance(arg_type, TupleType)
@@ -2260,17 +2261,17 @@ def is_valid_keyword_var_arg(self, typ: Type) -> bool:
         """Is a type valid as a **kwargs argument?"""
         if self.chk.options.python_version[0] >= 3:
             return is_subtype(typ, self.chk.named_generic_type(
-                'builtins.dict', [self.named_type('builtins.str'),
-                                  AnyType()]))
+                'typing.Mapping', [self.named_type('builtins.str'),
+                                   AnyType()]))
         else:
             return (
                 is_subtype(typ, self.chk.named_generic_type(
-                    'builtins.dict',
+                    'typing.Mapping',
                     [self.named_type('builtins.str'),
                      AnyType()]))
                 or
                 is_subtype(typ, self.chk.named_generic_type(
-                    'builtins.dict',
+                    'typing.Mapping',
                     [self.named_type('builtins.unicode'),
                      AnyType()])))
 

mypy/messages.py

@@ -740,12 +740,16 @@ def could_not_infer_type_arguments(self, callee_type: CallableType, n: int,
     def invalid_var_arg(self, typ: Type, context: Context) -> None:
         self.fail('List or tuple expected as variable arguments', context)
 
-    def invalid_keyword_var_arg(self, typ: Type, context: Context) -> None:
-        if isinstance(typ, Instance) and (typ.type.fullname() == 'builtins.dict'):
+    def invalid_keyword_var_arg(self, typ: Type, is_mapping: bool, context: Context) -> None:
+        if isinstance(typ, Instance) and is_mapping:
             self.fail('Keywords must be strings', context)
         else:
-            self.fail('Argument after ** must be a dictionary',
-                      context)
+            suffix = ''
+            if isinstance(typ, Instance):
+                suffix = ', not {}'.format(self.format(typ))
+            self.fail(
+                'Argument after ** must be a mapping{}'.format(suffix),
+                context)
 
     def undefined_in_superclass(self, member: str, context: Context) -> None:
         self.fail('"{}" undefined in superclass'.format(member), context)

test-data/unit/check-kwargs.test

@@ -280,12 +280,33 @@ reveal_type(formatter.__call__)  # E: Revealed type is 'def (message: builtins.s
 [builtins fixtures/bool.pyi]
 [out]
 
+[case testPassingMappingForKeywordVarArg]
+from typing import Mapping
+def f(**kwargs: 'A') -> None: pass
+b = None # type: Mapping
+d = None # type: Mapping[A, A]
+m = None # type: Mapping[str, A]
+f(**d)         # E: Keywords must be strings
+f(**m)
+f(**b)
+class A: pass
+[builtins fixtures/dict.pyi]
+
+[case testPassingMappingSubclassForKeywordVarArg]
+from typing import Mapping
+class MappingSubclass(Mapping[str, str]): pass
+def f(**kwargs: 'A') -> None: pass
+d = None # type: MappingSubclass
+f(**d)
+class A: pass
+[builtins fixtures/dict.pyi]
+
 [case testInvalidTypeForKeywordVarArg]
 from typing import Dict
-def f( **kwargs: 'A') -> None: pass
+def f(**kwargs: 'A') -> None: pass
 d = None # type: Dict[A, A]
 f(**d)         # E: Keywords must be strings
-f(**A())       # E: Argument after ** must be a dictionary
+f(**A())       # E: Argument after ** must be a mapping, not "A"
 class A: pass
 [builtins fixtures/dict.pyi]
 

test-data/unit/fixtures/args.pyi

@@ -1,6 +1,6 @@
 # Builtins stub used to support *args, **kwargs.
 
-from typing import TypeVar, Generic, Iterable, Tuple, Dict, Any, overload
+from typing import TypeVar, Generic, Iterable, Tuple, Dict, Any, overload, Mapping
 
 Tco = TypeVar('Tco', covariant=True)
 T = TypeVar('T')
@@ -19,7 +19,8 @@ class type:
     def __call__(self, *args: Any, **kwargs: Any) -> Any: pass
 
 class tuple(Iterable[Tco], Generic[Tco]): pass
-class dict(Generic[T, S]): pass
+
+class dict(Iterable[T], Mapping[T, S], Generic[T, S]): pass
 
 class int:
     def __eq__(self, o: object) -> bool: pass