Merge pull request #3732 from bryevdv/bryevdv/3731_protect_isenumclass

Protect isenumclass predicate against non-class arguments

sphinx/util/inspect.py

@@ -104,7 +104,7 @@ def isenumclass(x):
     """Check if the object is subclass of enum."""
     if enum is None:
         return False
-    return issubclass(x, enum.Enum)
+    return inspect.isclass(x) and issubclass(x, enum.Enum)
 
 
 def isenumattribute(x):