Allow **kwargs after bare asterisk (#2099)

Fix #142.

Author: elazarg

mypy/checkexpr.py

@@ -670,7 +670,7 @@ def check_argument_count(self, callee: CallableType, actual_types: List[Type],
                         messages.duplicate_argument_value(callee, i, context)
                     ok = False
             elif (kind == nodes.ARG_NAMED and formal_to_actual[i] and
-                  actual_kinds[formal_to_actual[i][0]] != nodes.ARG_NAMED):
+                  actual_kinds[formal_to_actual[i][0]] not in [nodes.ARG_NAMED, nodes.ARG_STAR2]):
                 # Positional argument when expecting a keyword argument.
                 if messages:
                     messages.too_many_positional_arguments(callee, context)

test-data/unit/check-kwargs.test

@@ -122,6 +122,15 @@ f(A(), B()) # E: Too many positional arguments for "f"
 class A: pass
 class B: pass
 
+[case testKwargsAfterBareArgs]
+from typing import Tuple, Any
+def f(a, *, b=None) -> None: pass
+a = None  # type: Any
+b = None  # type: Any
+f(a, **b)
+
+[builtins fixtures/dict.pyi]
+
 [case testKeywordArgAfterVarArgs]
 import typing
 def f(*a: 'A', b: 'B' = None,) -> None: pass