Fix constraint inference for TypedDict and Iterable[T] (#3611)

Fixes #3610.

Author: JukkaL

mypy/constraints.py

@@ -312,6 +312,8 @@ def visit_instance(self, template: Instance) -> List[Constraint]:
         res = []  # type: List[Constraint]
         if isinstance(actual, CallableType) and actual.fallback is not None:
             actual = actual.fallback
+        if isinstance(actual, TypedDictType):
+            actual = actual.as_anonymous().fallback
         if isinstance(actual, Instance):
             instance = actual
             if (self.direction == SUBTYPE_OF and

test-data/unit/check-typeddict.test

@@ -557,6 +557,17 @@ reveal_type(f(g)) # E: Revealed type is '<nothing>'
 
 -- Constraint Solver
 
+[case testTypedDictConstraintsAgainstIterable]
+from typing import TypeVar, Iterable
+from mypy_extensions import TypedDict
+T = TypeVar('T')
+def f(x: Iterable[T]) -> T: pass
+A = TypedDict('A', {'x': int})
+a: A
+reveal_type(f(a)) # E: Revealed type is 'builtins.str*'
+[builtins fixtures/dict.pyi]
+[typing fixtures/typing-full.pyi]
+
 -- TODO: Figure out some way to trigger the ConstraintBuilderVisitor.visit_typeddict_type() path.
 
 

test-data/unit/fixtures/dict.pyi

@@ -11,7 +11,7 @@ class object:
 
 class type: pass
 
-class dict(Iterable[KT], Mapping[KT, VT], Generic[KT, VT]):
+class dict(Mapping[KT, VT], Iterable[KT], Generic[KT, VT]):
     @overload
     def __init__(self, **kwargs: VT) -> None: pass
     @overload

test-data/unit/fixtures/typing-full.pyi

@@ -103,12 +103,12 @@ class Sequence(Iterable[T], Generic[T]):
     @abstractmethod
     def __getitem__(self, n: Any) -> T: pass
 
-class Mapping(Generic[T, U]):
+class Mapping(Iterable[T], Generic[T, U]):
     @overload
     def get(self, k: T) -> Optional[U]: ...
     @overload
     def get(self, k: T, default: Union[U, V]) -> Union[U, V]: ...
 
-class MutableMapping(Generic[T, U]): pass
+class MutableMapping(Mapping[T, U]): pass
 
 TYPE_CHECKING = 1