Annotated: backport bpo-46491 (#1049)

Author: GBeauregard

CHANGELOG

@@ -1,5 +1,7 @@
 # Release 4.x.x
 
+- `Annotated` can now wrap `ClassVar` and `Final`. Backport from
+  bpo-46491. Patch by Gregory Beauregard (@GBeauregard).
 - Add missed `Required` and `NotRequired` to `__all__`. Patch by
   Yuri Karabas (@uriyyo).
 - The `@final` decorator now sets the `__final__` attribute on the

src/test_typing_extensions.py

@@ -1799,6 +1799,24 @@ class C:
         A.x = 5
         self.assertEqual(C.x, 5)
 
+    @skipIf(sys.version_info[:2] in ((3, 9), (3, 10)), "Waiting for bpo-46491 bugfix.")
+    def test_special_form_containment(self):
+        class C:
+            classvar: Annotated[ClassVar[int], "a decoration"] = 4
+            const: Annotated[Final[int], "Const"] = 4
+
+        if sys.version_info[:2] >= (3, 7):
+            self.assertEqual(get_type_hints(C, globals())["classvar"], ClassVar[int])
+            self.assertEqual(get_type_hints(C, globals())["const"], Final[int])
+        else:
+            self.assertEqual(
+                get_type_hints(C, globals())["classvar"],
+                Annotated[ClassVar[int], "a decoration"]
+            )
+            self.assertEqual(
+                get_type_hints(C, globals())["const"], Annotated[Final[int], "Const"]
+            )
+
     def test_hash_eq(self):
         self.assertEqual(len({Annotated[int, 4, 5], Annotated[int, 4, 5]}), 1)
         self.assertNotEqual(Annotated[int, 4, 5], Annotated[int, 5, 4])

src/typing_extensions.py

@@ -1251,8 +1251,12 @@ def __class_getitem__(cls, params):
                 raise TypeError("Annotated[...] should be used "
                                 "with at least two arguments (a type and an "
                                 "annotation).")
-            msg = "Annotated[t, ...]: t must be a type."
-            origin = typing._type_check(params[0], msg)
+            allowed_special_forms = (ClassVar, Final)
+            if get_origin(params[0]) in allowed_special_forms:
+                origin = params[0]
+            else:
+                msg = "Annotated[t, ...]: t must be a type."
+                origin = typing._type_check(params[0], msg)
             metadata = tuple(params[1:])
             return _AnnotatedAlias(origin, metadata)
 
@@ -1377,8 +1381,14 @@ def __getitem__(self, params):
                                 "with at least two arguments (a type and an "
                                 "annotation).")
             else:
-                msg = "Annotated[t, ...]: t must be a type."
-                tp = typing._type_check(params[0], msg)
+                if (
+                    isinstance(params[0], typing._TypingBase) and
+                    type(params[0]).__name__ == "_ClassVar"
+                ):
+                    tp = params[0]
+                else:
+                    msg = "Annotated[t, ...]: t must be a type."
+                    tp = typing._type_check(params[0], msg)
                 metadata = tuple(params[1:])
             return self.__class__(
                 self.__name__,