From faa5f6053d7334a3ecc513c64947ac026439c03a Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Tue, 31 Oct 2023 21:53:57 +0100
Subject: gh-108765: Python.h no longer includes <stddef.h> on Windows
 (#111563)

In practice, only Windows is impacted, because the HAVE_STDDEF_H
macro was only defined on Windows.
---
 Doc/whatsnew/3.13.rst                                             | 8 ++++++++
 Include/Python.h                                                  | 3 ---
 .../next/C API/2023-10-31-18-22-03.gh-issue-108765._beYv8.rst     | 3 +++
 3 files changed, 11 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/C API/2023-10-31-18-22-03.gh-issue-108765._beYv8.rst

diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst
index 3a2df4f..1977902 100644
--- a/Doc/whatsnew/3.13.rst
+++ b/Doc/whatsnew/3.13.rst
@@ -1186,6 +1186,14 @@ Porting to Python 3.13
   ``PyUnicode_AsUTF8AndSize(unicode, NULL)`` can be used instead.
   (Contributed by Victor Stinner in :gh:`111089`.)
 
+* On Windows, ``Python.h`` no longer includes the ``<stddef.h>`` standard
+  header file. If needed, it should now be included explicitly. For example, it
+  provides ``offsetof()`` function, and ``size_t`` and ``ptrdiff_t`` types.
+  Including ``<stddef.h>`` explicitly was already needed by all other
+  platforms, the ``HAVE_STDDEF_H`` macro is only defined on Windows.
+  (Contributed by Victor Stinner in :gh:`108765`.)
+
+
 Deprecated
 ----------
 
diff --git a/Include/Python.h b/Include/Python.h
index 7312cc8..a1f26af 100644
--- a/Include/Python.h
+++ b/Include/Python.h
@@ -22,9 +22,6 @@
 #include <math.h>                 // HUGE_VAL
 #include <stdarg.h>               // va_list
 #include <wchar.h>                // wchar_t
-#ifdef HAVE_STDDEF_H
-#  include <stddef.h>             // size_t
-#endif
 #ifdef HAVE_SYS_TYPES_H
 #  include <sys/types.h>          // ssize_t
 #endif
diff --git a/Misc/NEWS.d/next/C API/2023-10-31-18-22-03.gh-issue-108765._beYv8.rst b/Misc/NEWS.d/next/C API/2023-10-31-18-22-03.gh-issue-108765._beYv8.rst
new file mode 100644
index 0000000..14af79e
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2023-10-31-18-22-03.gh-issue-108765._beYv8.rst	
@@ -0,0 +1,3 @@
+On Windows, ``Python.h`` no longer includes the ``<stddef.h>`` standard
+header file. If needed, it should now be included explicitly. Patch by
+Victor Stinner.
-- 
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