Fix #8350: autosummary_mock_imports causes slow down builds

The mock objects set up via `autosummary_mock_imports` causes slow down
of autosummary stub generation because AttributeDocumenter falls into
infinite recursion call to unwrap decorators of mocked objects.

To avoid the trouble, this blocks unwrapping decorators of mocked
objects.

CHANGES

@@ -19,6 +19,7 @@ Bugs fixed
 * #8372: autodoc: autoclass directive became slower than Sphinx-3.2
 * #7727: autosummary: raise PycodeError when documenting python package
   without __init__.py
+* #8350: autosummary: autosummary_mock_imports causes slow down builds
 * #8364: C, properly initialize attributes in empty symbols.
 * #8399: i18n: Put system locale path after the paths specified by configuration
 

sphinx/util/inspect.py

@@ -122,7 +122,11 @@ def getargspec(func: Callable) -> Any:
 def unwrap(obj: Any) -> Any:
     """Get an original object from wrapped object (wrapped functions)."""
     try:
-        return inspect.unwrap(obj)
+        if hasattr(obj, '__sphinx_mock__'):
+            # Skip unwrapping mock object to avoid RecursionError
+            return obj
+        else:
+            return inspect.unwrap(obj)
     except ValueError:
         # might be a mock object
         return obj