From c7e95715ec2f2a16eace7aa35a1eb2f18e8d06ed Mon Sep 17 00:00:00 2001
From: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
Date: Wed, 16 Jun 2021 23:34:52 +0800
Subject: [PATCH] [3.9] bpo-44392: Add Py_GenericAlias to C API docs (GH-26724)
 (GH-26757)

(cherry picked from commit 6773c3eaa735b5061b4a97f2c730703a32d8c9ff)
---
 Doc/c-api/concrete.rst                        |  1 +
 Doc/c-api/typehints.rst                       | 46 +++++++++++++++++++
 .../2021-06-16-18-09-49.bpo-44392.6RF1Sc.rst  |  2 +
 3 files changed, 49 insertions(+)
 create mode 100644 Doc/c-api/typehints.rst
 create mode 100644 Misc/NEWS.d/next/Documentation/2021-06-16-18-09-49.bpo-44392.6RF1Sc.rst

diff --git a/Doc/c-api/concrete.rst b/Doc/c-api/concrete.rst
index c1d9fa1b41a..84224dcca52 100644
--- a/Doc/c-api/concrete.rst
+++ b/Doc/c-api/concrete.rst
@@ -115,3 +115,4 @@ Other Objects
    coro.rst
    contextvars.rst
    datetime.rst
+   typehints.rst
diff --git a/Doc/c-api/typehints.rst b/Doc/c-api/typehints.rst
new file mode 100644
index 00000000000..2d1175f4738
--- /dev/null
+++ b/Doc/c-api/typehints.rst
@@ -0,0 +1,46 @@
+.. highlight:: c
+
+.. _typehintobjects:
+
+Objects for Type Hinting
+------------------------
+
+Various built-in types for type hinting are provided.
+Only :ref:`GenericAlias <types-genericalias>` is exposed to C.
+
+.. c:function:: PyObject* Py_GenericAlias(PyObject *origin, PyObject *args)
+
+   Create a :ref:`GenericAlias <types-genericalias>` object.
+   Equivalent to calling the Python class
+   :class:`types.GenericAlias`.  The *origin* and *args* arguments set the
+   ``GenericAlias``\ 's ``__origin__`` and ``__args__`` attributes respectively.
+   *origin* should be a :c:type:`PyTypeObject*`, and *args* can be a
+   :c:type:`PyTupleObject*` or any ``PyObject*``.  If *args* passed is
+   not a tuple, a 1-tuple is automatically constructed and ``__args__`` is set
+   to ``(args,)``.
+   Minimal checking is done for the arguments, so the function will succeed even
+   if *origin* is not a type.
+   The ``GenericAlias``\ 's ``__parameters__`` attribute is constructed lazily
+   from ``__args__``.  On failure, an exception is raised and ``NULL`` is
+   returned.
+
+   Here's an example of how to make an extension type generic::
+
+      ...
+      static PyMethodDef my_obj_methods[] = {
+          // Other methods.
+          ...
+          {"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS, "See PEP 585"}
+          ...
+      }
+
+   .. seealso:: The data model method :meth:`__class_getitem__`.
+
+   .. versionadded:: 3.9
+
+.. c:var:: PyTypeObject Py_GenericAliasType
+
+   The C type of the object returned by :c:func:`Py_GenericAlias`. Equivalent to
+   :class:`types.GenericAlias` in Python.
+
+   .. versionadded:: 3.9
diff --git a/Misc/NEWS.d/next/Documentation/2021-06-16-18-09-49.bpo-44392.6RF1Sc.rst b/Misc/NEWS.d/next/Documentation/2021-06-16-18-09-49.bpo-44392.6RF1Sc.rst
new file mode 100644
index 00000000000..ac197f22929
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2021-06-16-18-09-49.bpo-44392.6RF1Sc.rst
@@ -0,0 +1,2 @@
+Added a new section in the C API documentation for types used in type
+hinting.  Documented ``Py_GenericAlias`` and ``Py_GenericAliasType``.