bpo-38415: Allow using @asynccontextmanager-made ctx managers as decorators (GH-16667)

Lib/contextlib.py

@@ -191,6 +191,14 @@ class _AsyncGeneratorContextManager(
 ):
     """Helper for @asynccontextmanager decorator."""
 
+    def __call__(self, func):
+        @wraps(func)
+        async def inner(*args, **kwds):
+            async with self.__class__(self.func, self.args, self.kwds):
+                return await func(*args, **kwds)
+
+        return inner
+
     async def __aenter__(self):
         # do not keep args and kwds alive unnecessarily
         # they are only needed for recreation, which is not possible anymore