Fixed TypeError when checking a class against type[Self]

docs/versionhistory.rst

@@ -11,6 +11,8 @@ This library adheres to
   ``typing.no_type_check()`` (PR by @jolaf)
 - Fixed checking of variable assignments involving tuple unpacking
   (`#486 <https://github.com/agronholm/typeguard/pull/486>`_)
+- Fixed ``TypeError`` when checking a class against ``type[Self]``
+  (`#481 <https://github.com/agronholm/typeguard/pull/481>`_)
 
 **4.4.0** (2024-10-27)
 

src/typeguard/_checkers.py

@@ -464,6 +464,8 @@ def check_class(
 
     if expected_class is Any:
         return
+    elif expected_class is typing_extensions.Self:
+        check_self(value, get_origin(expected_class), get_args(expected_class), memo)
     elif getattr(expected_class, "_is_protocol", False):
         check_protocol(value, expected_class, (), memo)
     elif isinstance(expected_class, TypeVar):
@@ -847,8 +849,7 @@ def check_self(
     if isclass(value):
         if not issubclass(value, memo.self_type):
             raise TypeCheckError(
-                f"is not an instance of the self type "
-                f"({qualified_name(memo.self_type)})"
+                f"is not a subclass of the self type ({qualified_name(memo.self_type)})"
             )
     elif not isinstance(value, memo.self_type):
         raise TypeCheckError(

tests/test_checkers.py

@@ -36,6 +36,7 @@
 )
 
 import pytest
+from typing_extensions import LiteralString
 
 from typeguard import (
     CollectionCheckStrategy,
@@ -64,12 +65,9 @@
 )
 
 if sys.version_info >= (3, 11):
-    from typing import LiteralString
-
     SubclassableAny = Any
 else:
     from typing_extensions import Any as SubclassableAny
-    from typing_extensions import LiteralString
 
 if sys.version_info >= (3, 10):
     from typing import Concatenate, ParamSpec, TypeGuard

tests/test_typechecked.py

@@ -456,6 +456,29 @@ def method(cls, another: Self) -> None:
             rf"test_classmethod_arg_invalid\.<locals>\.Foo\)"
         )
 
+    def test_self_type_valid(self):
+        class Foo:
+            @typechecked
+            def method(cls, subclass: type[Self]) -> None:
+                pass
+
+        class Bar(Foo):
+            pass
+
+        Foo().method(Bar)
+
+    def test_self_type_invalid(self):
+        class Foo:
+            @typechecked
+            def method(cls, subclass: type[Self]) -> None:
+                pass
+
+        pytest.raises(TypeCheckError, Foo().method, int).match(
+            rf'argument "subclass" \(class int\) is not a subclass of the self type '
+            rf"\({__name__}\.{self.__class__.__name__}\."
+            rf"test_self_type_invalid\.<locals>\.Foo\)"
+        )
+
 
 class TestMock:
     def test_mock_argument(self):