Fix #8567: autodoc: Instance attributes are incorrectly added to Parent class

The instance attributes on subclasses are shown on the document of
parent class unexpectedly because of autodoc modifies `__annotations__`
in place.  This fix creates a copy of `__annotations__` attribute and
attach it to the subclass.

3 files changed, 11 insertions, 4 deletions

diff --git a/CHANGES b/CHANGES
index 6125b83a1..7241391ae 100644
--- a/CHANGES
+++ b/CHANGES
@@ -19,6 +19,7 @@ Bugs fixed
 * #8559: autodoc: AttributeError is raised when using forward-reference type
   annotations
 * #8568: autodoc: TypeError is raised on checking slots attribute
+* #8567: autodoc: Instance attributes are incorrectly added to Parent class
 
 Testing
 --------
diff --git a/sphinx/ext/autodoc/__init__.py b/sphinx/ext/autodoc/__init__.py
index 4bf97cc85..05696448d 100644
--- a/sphinx/ext/autodoc/__init__.py
+++ b/sphinx/ext/autodoc/__init__.py
@@ -1856,13 +1856,14 @@ class DataDocumenter(GenericAliasMixin, NewTypeMixin, TypeVarMixin,
     def update_annotations(self, parent: Any) -> None:
         """Update __annotations__ to support type_comment and so on."""
         try:
-            annotations = inspect.getannotations(parent)
+            annotations = dict(inspect.getannotations(parent))
+            parent.__annotations__ = annotations
 
             analyzer = ModuleAnalyzer.for_module(self.modname)
             analyzer.analyze()
             for (classname, attrname), annotation in analyzer.annotations.items():
                 if classname == '' and attrname not in annotations:
-                    annotations[attrname] = annotation  # type: ignore
+                    annotations[attrname] = annotation
         except AttributeError:
             pass
 
@@ -2292,7 +2293,8 @@ class AttributeDocumenter(GenericAliasMixin, NewTypeMixin, SlotsMixin,  # type:
     def update_annotations(self, parent: Any) -> None:
         """Update __annotations__ to support type_comment and so on."""
         try:
-            annotations = inspect.getannotations(parent)
+            annotations = dict(inspect.getannotations(parent))
+            parent.__annotations__ = annotations
 
             for cls in inspect.getmro(parent):
                 try:
@@ -2303,11 +2305,14 @@ class AttributeDocumenter(GenericAliasMixin, NewTypeMixin, SlotsMixin,  # type:
                     analyzer.analyze()
                     for (classname, attrname), annotation in analyzer.annotations.items():
                         if classname == qualname and attrname not in annotations:
-                            annotations[attrname] = annotation  # type: ignore
+                            annotations[attrname] = annotation
                 except (AttributeError, PycodeError):
                     pass
         except AttributeError:
             pass
+        except TypeError:
+            # Failed to set __annotations__ (built-in, extensions, etc.)
+            pass
 
     def import_object(self, raiseerror: bool = False) -> bool:
         try:
diff --git a/tests/test_ext_autodoc.py b/tests/test_ext_autodoc.py
index 392ad1a68..1fa0c1d7d 100644
--- a/tests/test_ext_autodoc.py
+++ b/tests/test_ext_autodoc.py
@@ -690,6 +690,7 @@ def test_autodoc_special_members(app):
     actual = do_autodoc(app, 'class', 'target.Class', options)
     assert list(filter(lambda l: '::' in l, actual)) == [
         '.. py:class:: Class(arg)',
+        '   .. py:attribute:: Class.__annotations__',
         '   .. py:attribute:: Class.__dict__',
         '   .. py:method:: Class.__init__(arg)',
         '   .. py:attribute:: Class.__module__',