gh-94912: Added marker for non-standard coroutine function detection (#99247)

This introduces a new decorator `@inspect.markcoroutinefunction`,
which, applied to a sync function, makes it appear async to
`inspect.iscoroutinefunction()`.

2 files changed, 29 insertions, 2 deletions

diff --git a/Doc/library/inspect.rst b/Doc/library/inspect.rst
index 6705577..58b84a3 100644
--- a/Doc/library/inspect.rst
+++ b/Doc/library/inspect.rst
@@ -343,8 +343,10 @@ attributes (see :ref:`import-mod-attrs` for module attributes):
 
 .. function:: iscoroutinefunction(object)
 
-   Return ``True`` if the object is a :term:`coroutine function`
-   (a function defined with an :keyword:`async def` syntax).
+   Return ``True`` if the object is a :term:`coroutine function` (a function
+   defined with an :keyword:`async def` syntax), a :func:`functools.partial`
+   wrapping a :term:`coroutine function`, or a sync function marked with
+   :func:`markcoroutinefunction`.
 
    .. versionadded:: 3.5
 
@@ -352,6 +354,25 @@ attributes (see :ref:`import-mod-attrs` for module attributes):
       Functions wrapped in :func:`functools.partial` now return ``True`` if the
       wrapped function is a :term:`coroutine function`.
 
+   .. versionchanged:: 3.12
+      Sync functions marked with :func:`markcoroutinefunction` now return
+      ``True``.
+
+
+.. function:: markcoroutinefunction(func)
+
+   Decorator to mark a callable as a :term:`coroutine function` if it would not
+   otherwise be detected by :func:`iscoroutinefunction`.
+
+   This may be of use for sync functions that return a :term:`coroutine`, if
+   the function is passed to an API that requires :func:`iscoroutinefunction`.
+
+   When possible, using an :keyword:`async def` function is preferred. Also
+   acceptable is calling the function and testing the return with
+   :func:`iscoroutine`.
+
+   .. versionadded:: 3.12
+
 
 .. function:: iscoroutine(object)
 
diff --git a/Doc/whatsnew/3.12.rst b/Doc/whatsnew/3.12.rst
index 73dc462..0cc4471 100644
--- a/Doc/whatsnew/3.12.rst
+++ b/Doc/whatsnew/3.12.rst
@@ -225,6 +225,12 @@ asyncio
   a custom event loop factory.
   (Contributed by Kumar Aditya in :gh:`99388`.)
 
+inspect
+-------
+
+* Add :func:`inspect.markcoroutinefunction` to mark sync functions that return
+  a :term:`coroutine` for use with :func:`iscoroutinefunction`.
+  (Contributed Carlton Gibson in :gh:`99247`.)
 
 pathlib
 -------