Fixed a bug that results in a false positive error when assigning a TypeGuard[T] or TypeIs[T] to a supertype of bool (like int). This addresses #8769. (#8771)

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

@@ -400,6 +400,7 @@ interface ScopedTypeVarResult {
 interface AliasMapEntry {
     alias: string;
     module: 'builtins' | 'collections' | 'self';
+    implicitBaseClass?: string;
     isSpecialForm?: boolean;
     isIllegalInIsinstance?: boolean;
     typeParamVariance?: Variance;
@@ -15083,10 +15084,7 @@ export function createTypeEvaluator(
         return type;
     }
 
-    // Creates a "TypeGuard" and "TypeIs" type. This is an alias for 'bool', which
-    // isn't a generic type and therefore doesn't have a typeParam.
-    // We'll abuse our internal types a bit by specializing it with
-    // a type argument anyway.
+    // Creates a "TypeGuard" and "TypeIs" type.
     function createTypeGuardType(
         classType: ClassType,
         errorNode: ParseNode,
@@ -15948,7 +15946,7 @@ export function createTypeEvaluator(
             specialClassType.shared.flags |= ClassTypeFlags.TypingExtensionClass;
         }
 
-        const baseClassName = aliasMapEntry.alias || 'object';
+        const baseClassName = aliasMapEntry.implicitBaseClass || aliasMapEntry.alias || 'object';
 
         let baseClass: Type | undefined;
         if (aliasMapEntry.module === 'builtins') {
@@ -16021,7 +16019,13 @@ export function createTypeEvaluator(
             ['Concatenate', { alias: '', module: 'builtins', isSpecialForm: true }],
             [
                 'TypeGuard',
-                { alias: '', module: 'builtins', isSpecialForm: true, typeParamVariance: Variance.Covariant },
+                {
+                    alias: '',
+                    module: 'builtins',
+                    implicitBaseClass: 'bool',
+                    isSpecialForm: true,
+                    typeParamVariance: Variance.Covariant,
+                },
             ],
             ['Unpack', { alias: '', module: 'builtins', isSpecialForm: true }],
             ['Required', { alias: '', module: 'builtins', isSpecialForm: true }],
@@ -16031,7 +16035,16 @@ export function createTypeEvaluator(
             ['Never', { alias: '', module: 'builtins', isSpecialForm: true }],
             ['LiteralString', { alias: '', module: 'builtins', isSpecialForm: true }],
             ['ReadOnly', { alias: '', module: 'builtins', isSpecialForm: true }],
-            ['TypeIs', { alias: '', module: 'builtins', isSpecialForm: true, typeParamVariance: Variance.Invariant }],
+            [
+                'TypeIs',
+                {
+                    alias: '',
+                    module: 'builtins',
+                    implicitBaseClass: 'bool',
+                    isSpecialForm: true,
+                    typeParamVariance: Variance.Invariant,
+                },
+            ],
         ]);
 
         const aliasMapEntry = specialTypes.get(assignedName);
@@ -22719,14 +22732,6 @@ export function createTypeEvaluator(
             return true;
         }
 
-        // If the type is a bool created with a `TypeGuard` or `TypeIs`, it is
-        // considered a subtype of `bool`.
-        if (isInstantiableClass(srcType) && ClassType.isBuiltIn(srcType, ['TypeGuard', 'TypeIs'])) {
-            if (isInstantiableClass(destType) && ClassType.isBuiltIn(destType, 'bool')) {
-                return (flags & AssignTypeFlags.Invariant) === 0;
-            }
-        }
-
         if ((flags & AssignTypeFlags.Invariant) === 0 || ClassType.isSameGenericClass(srcType, destType)) {
             if (isDerivedFrom) {
                 assert(inheritanceChain.length > 0);

packages/pyright-internal/src/tests/samples/typeGuard1.py

@@ -6,6 +6,7 @@
 
 import os
 from typing import Any, Callable, TypeVar
+
 from typing_extensions import TypeGuard  # pyright: ignore[reportMissingModuleSource]
 
 _T = TypeVar("_T")
@@ -124,3 +125,9 @@ takes_int_typeguard(bool_typeguard)
 
 # This should generate an error because TypeGuard is covariant.
 takes_int_typeguard(str_typeguard)
+
+
+v0 = is_int(int)
+v1: bool = v0
+v2: int = v0
+v3 = v0 & v0

packages/pyright-internal/src/tests/samples/typeIs1.py

@@ -172,3 +172,9 @@ def func10(
 
 def func10(v: tuple[int | str, ...], b: bool = True) -> bool:
     ...
+
+
+v0 = is_int(int)
+v1: bool = v0
+v2: int = v0
+v3 = v0 & v0