Fix sphinx-doc#9838: autodoc: AttributeError is raised for lru_cache

CHANGES

@@ -16,6 +16,9 @@ Features added
 Bugs fixed
 ----------
 
+* #9838: autodoc: AttributeError is raised on building document for functions
+  decorated by functools.lru_cache
+
 Testing
 --------
 

sphinx/util/inspect.py

@@ -19,8 +19,7 @@
 import warnings
 from functools import partial, partialmethod
 from importlib import import_module
-from inspect import (Parameter, isasyncgenfunction, isclass, ismethod,  # NOQA
-                     ismethoddescriptor, ismodule)
+from inspect import Parameter, isclass, ismethod, ismethoddescriptor, ismodule
 from io import StringIO
 from types import ModuleType
 from typing import Any, Callable, Dict, Mapping, Optional, Sequence, Tuple, Type, cast
@@ -408,6 +407,16 @@ def iswrappedcoroutine(obj: Any) -> bool:
         return False
 
 
+def isasyncgenfunction(obj: Any) -> bool:
+    """Check if the object is async-gen function."""
+    if hasattr(obj, '__code__') and inspect.isasyncgenfunction(obj):
+        # check obj.__code__ because isasyncgenfunction() crashes for custom method-like
+        # objects on python3.7 (see https://github.com/sphinx-doc/sphinx/issues/9838)
+        return True
+    else:
+        return False
+
+
 def isproperty(obj: Any) -> bool:
     """Check if the object is property."""
     if sys.version_info >= (3, 8):