Cover common isinstance calling patterns with some overloads

stdlib/@tests/test_cases/builtins/check_isinstance.py

@@ -0,0 +1,9 @@
+from typing import Any, cast
+from typing_extensions import TypeIs, assert_type
+
+o = cast(Any, "")
+assert_type(isinstance(o, int), TypeIs[int])
+assert_type(isinstance(o, object), TypeIs[object])
+assert_type(isinstance(o, str), TypeIs[str])
+assert_type(isinstance(o, (bytes, memoryview)), TypeIs[bytes | memoryview[int]])
+assert_type(isinstance(o, (set, type[dict])), TypeIs[set[Any] | type[dict[Any, Any]]])

stdlib/builtins.pyi

@@ -1882,7 +1882,27 @@ def iter(object: Callable[[], _T], sentinel: object, /) -> Iterator[_T]: ...
 
 _ClassInfo: TypeAlias = type | types.UnionType | tuple[_ClassInfo, ...]
 
+@overload
+def isinstance(obj: object, class_or_tuple: type[_T] | tuple[type[_T]], /) -> TypeIs[_T]: ...
+@overload
+def isinstance(obj: object, class_or_tuple: tuple[type[_T], type[_T1]], /) -> TypeIs[_T | _T1]: ...
+@overload
+def isinstance(obj: object, class_or_tuple: tuple[type[_T], type[_T1], type[_T2]], /) -> TypeIs[_T | _T1 | _T2]: ...
+@overload
+def isinstance(
+    obj: object, class_or_tuple: tuple[type[_T], type[_T1], type[_T2], type[_T3]], /
+) -> TypeIs[_T | _T1 | _T2 | _T3]: ...
+@overload
+def isinstance(
+    obj: object, class_or_tuple: tuple[type[_T], type[_T1], type[_T2], type[_T3], type[_T4]], /
+) -> TypeIs[_T | _T1 | _T2 | _T3 | _T4]: ...
+@overload
+def isinstance(
+    obj: object, class_or_tuple: tuple[type[_T], type[_T1], type[_T2], type[_T3], type[_T4], type[_T5]], /
+) -> TypeIs[_T | _T1 | _T2 | _T3 | _T4 | _T5]: ...
+@overload
 def isinstance(obj: object, class_or_tuple: _ClassInfo, /) -> bool: ...
+
 def issubclass(cls: type, class_or_tuple: _ClassInfo, /) -> bool: ...
 def len(obj: Sized, /) -> int: ...