Add a DeprecationWarning for when warnings.showwarning() is set to a function
that lacks support for the new 'line' argument.
diff --git a/Misc/NEWS b/Misc/NEWS
index 8515238..9c3743f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -42,7 +42,9 @@
machinery in such places as the parser where use of pure Python code is not
possible. Both the ``showarning()`` and ``formatwarning()`` gain an
optional 'line' argument which is not called by default for
- backwards-compatibility reasons.
+ backwards-compatibility reasons. Setting ``warnings.showwarning()`` to
+ an implementation that lacks support for the ``line`` argument will raise a
+ DeprecationWarning.
Library
-------