autodoc: Add Optional[t] to annotation of function and method

As typing.get_type_hints() doing, this adds Optional[t] to type
annotations if a default value equal to None is set.

Note: this is default behavior of inspect.signature() since Python 3.10.

1 files changed, 2 insertions, 2 deletions

diff --git a/sphinx/util/inspect.py b/sphinx/util/inspect.py
index 1eaccb678..92c6ac7fb 100644
--- a/sphinx/util/inspect.py
+++ b/sphinx/util/inspect.py
@@ -470,10 +470,10 @@ def signature(subject: Callable, bound_method: bool = False, follow_wrapped: boo
             raise
 
     try:
-        # Update unresolved annotations using ``get_type_hints()``.
+        # Resolve forwared reference annotations using ``get_type_hints()`` and type_aliases.
         annotations = typing.get_type_hints(subject, None, type_aliases)
         for i, param in enumerate(parameters):
-            if isinstance(param.annotation, str) and param.name in annotations:
+            if param.name in annotations:
                 parameters[i] = param.replace(annotation=annotations[param.name])
         if 'return' in annotations:
             return_annotation = annotations['return']