Added special-case handling x in y narrowing logic for the case whe…

…re `x` is a `dict` or `Mapping` and `y` is an iterable of `TypedDict`s. This addresses #6436.

packages/pyright-internal/src/analyzer/typeGuards.ts

@@ -2051,6 +2051,15 @@ export function narrowTypeForContainerElementType(evaluator: TypeEvaluator, refe
             return referenceType;
         }
 
+        // Handle the special case where the reference type is a dict or Mapping and
+        // the element type is a TypedDict. In this case, we can't say whether there
+        // is a type overlap, so don't apply narrowing.
+        if (isClassInstance(referenceType) && ClassType.isBuiltIn(referenceType, ['dict', 'Mapping'])) {
+            if (isClassInstance(concreteElementType) && ClassType.isTypedDictClass(concreteElementType)) {
+                return concreteElementType;
+            }
+        }
+
         if (evaluator.assignType(referenceType, concreteElementType)) {
             return concreteElementType;
         }

packages/pyright-internal/src/tests/samples/typeNarrowingIn1.py

@@ -1,6 +1,6 @@
 # This sample tests type narrowing for the "in" operator.
 
-from typing import Literal
+from typing import Literal, TypedDict
 import random
 
 
@@ -138,3 +138,18 @@ def func10(x: Literal["A", "B"], y: tuple[Literal["A"], ...]):
         reveal_type(x, expected_text="Literal['A']")
     else:
         reveal_type(x, expected_text="Literal['A', 'B']")
+
+
+class TD1(TypedDict):
+    x: str
+
+
+class TD2(TypedDict):
+    y: str
+
+
+def func11(x: dict[str, str]):
+    if x in (TD1(x="a"), TD2(y="b")):
+        reveal_type(x, expected_text="TD1 | TD2")
+    else:
+        reveal_type(x, expected_text="dict[str, str]")

packages/pyright-internal/src/tests/samples/typeNarrowingIn2.py

@@ -23,3 +23,4 @@ def func2(x: MyEnum):
         reveal_type(x, expected_text="Literal[MyEnum.A, MyEnum.B]")
     else:
         reveal_type(x, expected_text="Literal[MyEnum.C]")
+