Minimal changes to make filter() test pass

Author: gvanrossum

mypy/constraints.py

@@ -457,7 +457,12 @@ def visit_callable_type(self, template: CallableType) -> List[Constraint]:
                 for t, a in zip(template.arg_types, cactual.arg_types):
                     # Negate direction due to function argument type contravariance.
                     res.extend(infer_constraints(t, a, neg_op(self.direction)))
-            res.extend(infer_constraints(template.ret_type, cactual.ret_type,
+            template_ret_type, cactual_ret_type = template.ret_type, cactual.ret_type
+            if template.type_guard is not None:
+                template_ret_type = template.type_guard
+            if cactual.type_guard is not None:
+                cactual_ret_type = cactual.type_guard
+            res.extend(infer_constraints(template_ret_type, cactual_ret_type,
                                          self.direction))
             return res
         elif isinstance(self.actual, AnyType):

mypy/expandtype.py

@@ -96,8 +96,12 @@ def visit_type_var(self, t: TypeVarType) -> Type:
             return repl
 
     def visit_callable_type(self, t: CallableType) -> Type:
+        extra = {}
+        if t.type_guard is not None:
+            extra['type_guard'] = t.type_guard.accept(self)
         return t.copy_modified(arg_types=self.expand_types(t.arg_types),
-                               ret_type=t.ret_type.accept(self))
+                               ret_type=t.ret_type.accept(self),
+                               **extra)
 
     def visit_overloaded(self, t: Overloaded) -> Type:
         items = []  # type: List[CallableType]

test-data/unit/check-typeguard.test

@@ -118,8 +118,8 @@ R = TypeVar('R')
 def filter(f: Callable[[T], TypeGuard[R]], it: Iterable[T]) -> Iterable[R]: pass
 def is_float(a: object) -> TypeGuard[float]: pass
 a: List[object] = ["a", 0, 0.0]
-# TODO: Make this pass
-##reveal_type(filter(is_float, a))  ## N: Revealed type is 'typing.Iterable[float]'
+b = filter(is_float, a)
+reveal_type(b)  # N: Revealed type is 'typing.Iterable[builtins.float*]'
 [builtins fixtures/tuple.pyi]
 
 [case testTypeGuardWalrus]