gh-154136: Define _ISOC23_SOURCE to fix building the math module on FreeBSD

serhiy-storchaka · claude · serhiy-storchaka · commit aaf085fd3523 · 2026-07-19T16:59:51.000+03:00
Co-Authored-By: Claude Fable 5 &lt;noreply@anthropic.com&gt;
diff --git a/Misc/NEWS.d/next/Build/2026-07-19-16-45-00.gh-issue-154136.mathpi.rst b/Misc/NEWS.d/next/Build/2026-07-19-16-45-00.gh-issue-154136.mathpi.rst
@@ -0,0 +1,3 @@
+Fix building the :mod:`math` module on FreeBSD.
+Define ``_ISOC23_SOURCE`` to make the C23 library declarations
+(such as ``sinpi()`` in ``math.h``) visible.
diff --git a/configure b/configure
diff --git a/configure.ac b/configure.ac
@@ -935,6 +935,12 @@ then
 
   AC_DEFINE([_POSIX_C_SOURCE], [202405L],
             [Define to activate features from IEEE Std 1003.1-2024])
+
+  # Defining _POSIX_C_SOURCE and _XOPEN_SOURCE hides C23 library
+  # declarations on FreeBSD (e.g. sinpi() in math.h) when compiling
+  # with -std=c11.  Defining _ISOC23_SOURCE makes them visible again.
+  AC_DEFINE([_ISOC23_SOURCE], [1],
+            [Define to activate ISO C23 library declarations])
 fi
 
 # On HP-UX mbstate_t requires _INCLUDE__STDC_A1_SOURCE
diff --git a/pyconfig.h.in b/pyconfig.h.in
@@ -2143,6 +2143,9 @@
 /* Define to include mbstate_t for mbrtowc */
 #undef _INCLUDE__STDC_A1_SOURCE
 
+/* Define to activate ISO C23 library declarations */
+#undef _ISOC23_SOURCE
+
 /* This must be defined on some systems to enable large file support. */
 #undef _LARGEFILE_SOURCE
 

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Fix building the :mod:`math` module on FreeBSD.
	`2`	+Define ``_ISOC23_SOURCE`` to make the C23 library declarations
	`3`	+(such as ``sinpi()`` in ``math.h``) visible.