Implement closed support in TypeAnalyser

Propagate closed when analysing a TypedDictType with a fallback. This
ensures subtype checks work correctly for a TypeVar with a closed
TypedDict upper bound.

Author: alicederyn

mypy/typeanal.py

@@ -1347,6 +1347,7 @@ def visit_typeddict_type(self, t: TypedDictType) -> Type:
                     " must be enabled with --enable-incomplete-feature=InlineTypedDict",
                     t,
                 )
+            is_closed = False
             required_keys = req_keys
             fallback = self.named_type("typing._TypedDict")
             for typ in t.extra_items_from:
@@ -1369,9 +1370,9 @@ def visit_typeddict_type(self, t: TypedDictType) -> Type:
             readonly_keys = t.readonly_keys
             required_keys = t.required_keys
             fallback = t.fallback
-        # TODO: Implement closure analysis
+            is_closed = t.is_closed
         return TypedDictType(
-            items, required_keys, readonly_keys, False, fallback, t.line, t.column
+            items, required_keys, readonly_keys, is_closed, fallback, t.line, t.column
         )
 
     def visit_raw_expression_type(self, t: RawExpressionType) -> Type:

test-data/unit/check-typeddict.test

@@ -5288,6 +5288,23 @@ f_g(h)  # E: Argument 1 to "f_g" has incompatible type "H"; expected "G"
 [builtins fixtures/dict.pyi]
 [typing fixtures/typing-typeddict.pyi]
 
+[case testTypedDictSubtypingClosedTypeVarBound]
+from typing import TypedDict, TypeVar
+A = TypedDict('A', {'x': int}, closed=True)
+B = TypedDict('B', {'x': int})
+TA = TypeVar('TA', bound=A)
+TB = TypeVar('TB', bound=B)
+def fA(t: TA) -> TA: return t
+def fB(t: TB) -> TB: return t
+a: A
+b: B
+fA(a)
+fA(b)  # E: Value of type variable "TA" of "fA" cannot be "B"
+fB(a)
+fB(b)
+[builtins fixtures/dict.pyi]
+[typing fixtures/typing-typeddict.pyi]
+
 [case testJoinOfClosedTypedDict]
 from typing import TypedDict, TypeVar
 A = TypedDict('A', {'x': int}, closed=True)