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gh-155321: Avoid Python.h POSIX macro redefinition #155343

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gh-155321: Avoid Python.h POSIX macro redefinition #155343

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gh-155321: Avoid Python.h POSIX macro redefinition
RealBhupesh Aug 7, 2026
69983c8
gh-155321: Regenerate pyconfig.h.in
RealBhupesh Aug 7, 2026
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Build/2026-08-07-00-00-00.gh-issue-155321.pythonh-posix.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Allow :file:`Python.h` to be included after system headers that define
``_POSIX_C_SOURCE`` without causing a macro redefinition diagnostic.

@aisk aisk Aug 7, 2026 •
edited
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I think the filename should follow the naming convention of other news entries. In particular, the timestamp should be the actual time rather than a zero timestamp, and the final part should be a random string

Blurb and blurb-it are the recommended tools for generating news entries. See: https://devguide.python.org/getting-started/pull-request-lifecycle/#how-to-add-a-news-entry

2 changes: 1 addition & 1 deletion configure
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13 changes: 11 additions & 2 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -237,6 +237,15 @@ AH_BOTTOM([
#define STRICT_SYSV_CURSES /* Don't use ncurses extensions */
#endif

/* Define _POSIX_C_SOURCE only when it was not defined by an earlier
system-header include. */
#ifdef _PYTHON_POSIX_C_SOURCE
# ifndef _POSIX_C_SOURCE
# define _POSIX_C_SOURCE 202405L
# endif
# undef _PYTHON_POSIX_C_SOURCE
#endif

#endif /*Py_PYCONFIG_H*/
])

Expand Down Expand Up @@ -930,8 +939,8 @@ then
AC_DEFINE([_XOPEN_SOURCE_EXTENDED], [1],
[Define to activate Unix95-and-earlier features])

AC_DEFINE([_POSIX_C_SOURCE], [202405L],
[Define to activate features from IEEE Std 1003.1-2024])
AC_DEFINE([_PYTHON_POSIX_C_SOURCE], [1],
[Define to configure _POSIX_C_SOURCE in pyconfig.h])
Comment on lines +942 to +943

@chatgpt-codex-connector chatgpt-codex-connector Bot Aug 7, 2026

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P2 Badge Preserve the POSIX macro during configure probes

When configuring on a target where _XOPEN_SOURCE alone does not expose the required POSIX declarations—specifically Tru64 and some HP-UX cases called out immediately above—this replacement leaves only _PYTHON_POSIX_C_SOURCE in confdefs.h; the conditional that turns it into _POSIX_C_SOURCE exists only in the generated pyconfig.h. Consequently, all subsequent configure header/function probes run without the required feature-test macro and can record false-negative HAVE_* results, even though the actual Python build later sees _POSIX_C_SOURCE=202405L. Preserve the real macro for configure test compilations while using the marker only for generating the guarded public-header definition.

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# Defining _POSIX_C_SOURCE and _XOPEN_SOURCE hides C23 library
# declarations on FreeBSD (e.g. sinpi() in math.h) when compiling
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15 changes: 12 additions & 3 deletions pyconfig.h.in
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Expand Up @@ -2161,15 +2161,15 @@
/* Define on NetBSD to activate all library features */
#undef _NETBSD_SOURCE

/* Define to activate features from IEEE Std 1003.1-2024 */
#undef _POSIX_C_SOURCE

/* Define if you have POSIX threads, and your system does not define that. */
#undef _POSIX_THREADS

/* framework name */
#undef _PYTHONFRAMEWORK

/* Define to configure _POSIX_C_SOURCE in pyconfig.h */
#undef _PYTHON_POSIX_C_SOURCE

/* Maximum length in bytes of a thread name */
#undef _PYTHREAD_NAME_MAXLEN

Expand Down Expand Up @@ -2263,5 +2263,14 @@
#define STRICT_SYSV_CURSES /* Don't use ncurses extensions */
#endif

/* Define _POSIX_C_SOURCE only when it was not defined by an earlier
system-header include. */
#ifdef _PYTHON_POSIX_C_SOURCE
# ifndef _POSIX_C_SOURCE
# define _POSIX_C_SOURCE 202405L
# endif
# undef _PYTHON_POSIX_C_SOURCE
#endif

#endif /*Py_PYCONFIG_H*/

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