Fixed a bug that leads to incorrect (unsound) type narrowing when usi…

…ng the `x in y` type guard pattern. The `in` operator uses equality checks, and `__eq__` can succeed for objects of disjoint types, which means disjointedness cannot be used as the basis for narrowing here. This change also affects the `reportUnnecessaryContains` check, which leverages the same logic. This addresses #9338. (#9868)

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

@@ -2125,7 +2125,7 @@ export class Checker extends ParseTreeWalker {
                         return;
                     }
 
-                    if (this._isTypeComparable(leftSubtype, rightSubtype)) {
+                    if (this._evaluator.isTypeComparable(leftSubtype, rightSubtype)) {
                         isComparable = true;
                     }
 
@@ -2151,97 +2151,6 @@ export class Checker extends ParseTreeWalker {
         }
     }
 
-    // Determines whether the two types are potentially comparable -- i.e.
-    // their types overlap in such a way that it makes sense for them to
-    // be compared with an == or != operator.
-    private _isTypeComparable(leftType: Type, rightType: Type) {
-        if (isAnyOrUnknown(leftType) || isAnyOrUnknown(rightType)) {
-            return true;
-        }
-
-        if (isNever(leftType) || isNever(rightType)) {
-            return false;
-        }
-
-        if (isModule(leftType) || isModule(rightType)) {
-            return isTypeSame(leftType, rightType, { ignoreConditions: true });
-        }
-
-        const isLeftCallable = isFunction(leftType) || isOverloaded(leftType);
-        const isRightCallable = isFunction(rightType) || isOverloaded(rightType);
-        if (isLeftCallable !== isRightCallable) {
-            return false;
-        }
-
-        if (isInstantiableClass(leftType) || (isClassInstance(leftType) && ClassType.isBuiltIn(leftType, 'type'))) {
-            if (
-                isInstantiableClass(rightType) ||
-                (isClassInstance(rightType) && ClassType.isBuiltIn(rightType, 'type'))
-            ) {
-                const genericLeftType = ClassType.specialize(leftType, /* typeArgs */ undefined);
-                const genericRightType = ClassType.specialize(rightType, /* typeArgs */ undefined);
-
-                if (
-                    this._evaluator.assignType(genericLeftType, genericRightType) ||
-                    this._evaluator.assignType(genericRightType, genericLeftType)
-                ) {
-                    return true;
-                }
-            }
-
-            // Does the class have an operator overload for eq?
-            const metaclass = leftType.shared.effectiveMetaclass;
-            if (metaclass && isClass(metaclass)) {
-                if (lookUpClassMember(metaclass, '__eq__', MemberAccessFlags.SkipObjectBaseClass)) {
-                    return true;
-                }
-            }
-
-            return false;
-        }
-
-        if (isClassInstance(leftType)) {
-            if (isClass(rightType)) {
-                const genericLeftType = ClassType.specialize(leftType, /* typeArgs */ undefined);
-                const genericRightType = ClassType.specialize(rightType, /* typeArgs */ undefined);
-
-                if (
-                    this._evaluator.assignType(genericLeftType, genericRightType) ||
-                    this._evaluator.assignType(genericRightType, genericLeftType)
-                ) {
-                    return true;
-                }
-
-                // Assume that if the types are disjoint and built-in classes that they
-                // will never be comparable.
-                if (ClassType.isBuiltIn(leftType) && ClassType.isBuiltIn(rightType) && TypeBase.isInstance(rightType)) {
-                    return false;
-                }
-            }
-
-            // Does the class have an operator overload for eq?
-            const eqMethod = lookUpClassMember(
-                ClassType.cloneAsInstantiable(leftType),
-                '__eq__',
-                MemberAccessFlags.SkipObjectBaseClass
-            );
-
-            if (eqMethod) {
-                // If this is a synthesized method for a dataclass, we can assume
-                // that other dataclass types will not be comparable.
-                if (ClassType.isDataClass(leftType) && eqMethod.symbol.getSynthesizedType()) {
-                    return false;
-                }
-
-                return true;
-            }
-
-            return false;
-        }
-
-        return true;
-    }
-
     // If the function is a generator, validates that its annotated return type
     // is appropriate for a generator.
     private _validateGeneratorReturnType(node: FunctionNode, functionType: FunctionType) {

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

@@ -25540,6 +25540,120 @@ export function createTypeEvaluator(
         );
     }
 
+    // Determines whether the two types are potentially comparable -- i.e.
+    // their types overlap in such a way that it makes sense for them to
+    // be compared with an == or != operator.
+    function isTypeComparable(leftType: Type, rightType: Type) {
+        if (isAnyOrUnknown(leftType) || isAnyOrUnknown(rightType)) {
+            return true;
+        }
+
+        if (isNever(leftType) || isNever(rightType)) {
+            return false;
+        }
+
+        if (isModule(leftType) || isModule(rightType)) {
+            return isTypeSame(leftType, rightType, { ignoreConditions: true });
+        }
+
+        const isLeftCallable = isFunction(leftType) || isOverloaded(leftType);
+        const isRightCallable = isFunction(rightType) || isOverloaded(rightType);
+        if (isLeftCallable !== isRightCallable) {
+            return false;
+        }
+
+        if (isInstantiableClass(leftType) || (isClassInstance(leftType) && ClassType.isBuiltIn(leftType, 'type'))) {
+            if (
+                isInstantiableClass(rightType) ||
+                (isClassInstance(rightType) && ClassType.isBuiltIn(rightType, 'type'))
+            ) {
+                const genericLeftType = ClassType.specialize(leftType, /* typeArgs */ undefined);
+                const genericRightType = ClassType.specialize(rightType, /* typeArgs */ undefined);
+
+                if (assignType(genericLeftType, genericRightType) || assignType(genericRightType, genericLeftType)) {
+                    return true;
+                }
+            }
+
+            // Does the class have an operator overload for eq?
+            const metaclass = leftType.shared.effectiveMetaclass;
+            if (metaclass && isClass(metaclass)) {
+                if (lookUpClassMember(metaclass, '__eq__', MemberAccessFlags.SkipObjectBaseClass)) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        if (isClassInstance(leftType)) {
+            if (isClass(rightType)) {
+                const genericLeftType = ClassType.specialize(leftType, /* typeArgs */ undefined);
+                const genericRightType = ClassType.specialize(rightType, /* typeArgs */ undefined);
+
+                if (assignType(genericLeftType, genericRightType) || assignType(genericRightType, genericLeftType)) {
+                    return true;
+                }
+
+                // Assume that if the types are disjoint and built-in classes that they
+                // will never be comparable.
+                if (ClassType.isBuiltIn(leftType) && ClassType.isBuiltIn(rightType) && TypeBase.isInstance(rightType)) {
+                    // We need to be careful with bool and int literals because
+                    // they are comparable under certain circumstances.
+                    let boolType: ClassType | undefined;
+                    let intType: ClassType | undefined;
+                    if (ClassType.isBuiltIn(leftType, 'bool') && ClassType.isBuiltIn(rightType, 'int')) {
+                        boolType = leftType;
+                        intType = rightType;
+                    } else if (ClassType.isBuiltIn(rightType, 'bool') && ClassType.isBuiltIn(leftType, 'int')) {
+                        boolType = rightType;
+                        intType = leftType;
+                    }
+
+                    if (boolType && intType) {
+                        const intVal = intType.priv?.literalValue as number | BigInt | undefined;
+                        if (intVal === undefined) {
+                            return true;
+                        }
+                        if (intVal !== 0 && intVal !== 1) {
+                            return false;
+                        }
+
+                        const boolVal = boolType.priv?.literalValue as boolean | undefined;
+                        if (boolVal === undefined) {
+                            return true;
+                        }
+
+                        return boolVal === (intVal === 1);
+                    }
+
+                    return false;
+                }
+            }
+
+            // Does the class have an operator overload for eq?
+            const eqMethod = lookUpClassMember(
+                ClassType.cloneAsInstantiable(leftType),
+                '__eq__',
+                MemberAccessFlags.SkipObjectBaseClass
+            );
+
+            if (eqMethod) {
+                // If this is a synthesized method for a dataclass, we can assume
+                // that other dataclass types will not be comparable.
+                if (ClassType.isDataClass(leftType) && eqMethod.symbol.getSynthesizedType()) {
+                    return false;
+                }
+
+                return true;
+            }
+
+            return false;
+        }
+
+        return true;
+    }
+
     function assignToUnionType(
         destType: UnionType,
         srcType: Type,
@@ -28325,6 +28439,7 @@ export function createTypeEvaluator(
         getCallSignatureInfo,
         getAbstractSymbols,
         narrowConstrainedTypeVar,
+        isTypeComparable,
         assignType,
         validateOverrideMethod,
         validateCallArgs,

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

@@ -768,6 +768,7 @@ export interface TypeEvaluator {
     getCallSignatureInfo: (node: CallNode, activeIndex: number, activeOrFake: boolean) => CallSignatureInfo | undefined;
     getAbstractSymbols: (classType: ClassType) => AbstractSymbol[];
     narrowConstrainedTypeVar: (node: ParseNode, typeVar: TypeVarType) => Type | undefined;
+    isTypeComparable: (leftType: Type, rightType: Type) => boolean;
 
     assignType: (
         destType: Type,

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

@@ -2066,15 +2066,40 @@ export function narrowTypeForContainerElementType(evaluator: TypeEvaluator, refe
                 return referenceSubtype;
             }
 
-            if (evaluator.assignType(referenceSubtype, elementSubtype)) {
+            // If the two types are disjoint (i.e. are not comparable), eliminate this subtype.
+            if (!evaluator.isTypeComparable(elementSubtype, referenceSubtype)) {
+                return undefined;
+            }
+
+            // If one of the two types is a literal, we can narrow to that type.
+            if (
+                isClassInstance(elementSubtype) &&
+                (isLiteralType(elementSubtype) || isNoneInstance(elementSubtype)) &&
+                evaluator.assignType(referenceSubtype, elementSubtype)
+            ) {
                 return stripTypeForm(addConditionToType(elementSubtype, referenceSubtype.props?.condition));
             }
 
-            if (evaluator.assignType(elementSubtype, referenceSubtype)) {
+            if (
+                isClassInstance(referenceSubtype) &&
+                (isLiteralType(referenceSubtype) || isNoneInstance(referenceSubtype)) &&
+                evaluator.assignType(elementSubtype, referenceSubtype)
+            ) {
                 return stripTypeForm(addConditionToType(referenceSubtype, elementSubtype.props?.condition));
             }
 
-            return undefined;
+            // If the element type is a known class object that is assignable to
+            // the reference type, we can narrow to that class object.
+            if (
+                isInstantiableClass(elementSubtype) &&
+                !elementSubtype.priv.includeSubclasses &&
+                evaluator.assignType(referenceSubtype, elementSubtype)
+            ) {
+                return stripTypeForm(addConditionToType(elementSubtype, referenceSubtype.props?.condition));
+            }
+
+            // It's not safe to narrow.
+            return referenceSubtype;
         });
     });
 }

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

@@ -85,10 +85,10 @@ def func6(x: type):
 
 def func7(x: object | bytes, y: str, z: int):
     if x in (y, z):
-        reveal_type(x, expected_text="str | int")
+        reveal_type(x, expected_text="object")
     else:
         reveal_type(x, expected_text="object | bytes")
-    reveal_type(x, expected_text="str | int | object | bytes")
+    reveal_type(x, expected_text="object | bytes")
 
 
 def func8(x: object):
@@ -127,13 +127,6 @@ 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]")
-
-
 T1 = TypeVar("T1", TD1, TD2)
 
 
@@ -175,4 +168,39 @@ def func14(x: str, y: dict[Any, Any]):
 
 def func15(x: Any, y: dict[str, str]):
     if x in y:
-        reveal_type(x, expected_text="str")
+        reveal_type(x, expected_text="Any")
+
+
+def func16(x: int, y: list[Literal[0, 1]]):
+    if x in y:
+        reveal_type(x, expected_text="Literal[0, 1]")
+
+
+def func17(x: Literal[-1, 0], y: list[Literal[0, 1]]):
+    if x in y:
+        reveal_type(x, expected_text="Literal[0]")
+
+
+def func18(x: Literal[0, 1, 2], y: list[Literal[0, 1]]):
+    if x in y:
+        reveal_type(x, expected_text="Literal[0, 1]")
+
+
+def func19(x: float, y: list[int]):
+    if x in y:
+        reveal_type(x, expected_text="float")
+
+
+def func20(x: float, y: list[Literal[0, 1]]):
+    if x in y:
+        reveal_type(x, expected_text="Literal[0, 1]")
+
+
+def func21(x: int, y: list[Literal[0, True]]):
+    if x in y:
+        reveal_type(x, expected_text="Literal[0, True]")
+
+
+def func22(x: bool, y: list[Literal[0, 1]]):
+    if x in y:
+        reveal_type(x, expected_text="bool")

packages/pyright-internal/src/tests/samples/unnecessaryContains1.py

@@ -34,7 +34,7 @@ def func3(x: list[str]):
         return
 
     # This should generate an error if "reportUnnecessaryContains" is enabled.
-    if x not in ([1, 2], [3]):
+    if x not in ((1, 2), (3,)):
         pass