Fix sphinx-doc#8200: autodoc: type aliases break type formatting

The annotation option is shared between auto directives unexpectedly.
It causes supression of type annotations for objects after
GenericAlias definition.

CHANGES

@@ -19,6 +19,7 @@ Bugs fixed
 * #8085: i18n: Add support for having single text domain
 * #8143: autodoc: AttributeError is raised when False value is passed to
   autodoc_default_options
+* #8200: autodoc: type aliases break type formatting of autoattribute
 * #8093: The highlight warning has wrong location in some builders (LaTeX,
   singlehtml and so on)
 

sphinx/ext/autodoc/__init__.py

@@ -1707,7 +1707,8 @@ def can_document_member(cls, member: Any, membername: str, isattr: bool, parent:
         return inspect.isgenericalias(member)
 
     def add_directive_header(self, sig: str) -> None:
-        self.options.annotation = SUPPRESS  # type: ignore
+        self.options = Options(self.options)
+        self.options['annotation'] = SUPPRESS
         super().add_directive_header(sig)
 
     def add_content(self, more_content: Any, no_docstring: bool = False) -> None:
@@ -1731,7 +1732,8 @@ def can_document_member(cls, member: Any, membername: str, isattr: bool, parent:
         return isinstance(member, TypeVar) and isattr  # type: ignore
 
     def add_directive_header(self, sig: str) -> None:
-        self.options.annotation = SUPPRESS  # type: ignore
+        self.options = Options(self.options)
+        self.options['annotation'] = SUPPRESS
         super().add_directive_header(sig)
 
     def get_doc(self, encoding: str = None, ignore: int = None) -> List[List[str]]: