If module is _io, use io instead (#291)

Most of the io module is implemented in the private C extension
module called _io. It would be friendly if Python set the module
name to io to match the way it is documented but they don't.

Author: hoodmane

src/sphinx_autodoc_typehints/__init__.py

@@ -139,6 +139,9 @@ def format_annotation(annotation: Any, config: Config) -> str:  # noqa: C901 # t
     if module == "typing_extensions":
         module = "typing"
 
+    if module == "_io":
+        module = "io"
+
     full_name = f"{module}.{class_name}" if module != "builtins" else class_name
     fully_qualified: bool = getattr(config, "typehints_fully_qualified", False)
     prefix = "" if fully_qualified or full_name == class_name else "~"

tests/test_sphinx_autodoc_typehints.py

@@ -180,6 +180,7 @@ def test_parse_annotation(annotation: Any, module: str, class_name: str, args: t
     [
         (str, ":py:class:`str`"),
         (int, ":py:class:`int`"),
+        (StringIO, ":py:class:`~io.StringIO`"),
         (type(None), ":py:obj:`None`"),
         (type, ":py:class:`type`"),
         (collections.abc.Callable, ":py:class:`~collections.abc.Callable`"),