Building Python 3.11 fails to build on FreeBSD 12: static_assert() is not defined by <assert.h> #91782
Description
Python 3.11 no longer builds on FreeBSD 12 since the commit 7cdaf87 that I made yesterday.
My change: #91730
I checked with buildbots that Python still builds successfully on FreeBSD. It did on the two FreeBSD buildbot workers. Problem: one FreeBSD worker failed to download code with Git and the build was marked as successful :-(
Successful build+test on FreeBSD:
- https://buildbot.python.org/all/#/builders/203/builds/582
- https://buildbot.python.org/all/#/builders/387/builds/510
git failed on the second job!
fatal: bad object refs/heads/refs/pull/28569
error: https://github.com/python/cpython.git did not send all necessary objects
(...)
fatal: failed to run reflog
error: task 'gc' failed
program finished with exit code 1
And now Python fails to build on "AMD64 FreeBSD Non-Debug 3.x" which runs FreeBSD 12.3: https://buildbot.python.org/all/#/builders/172/builds/1911
test.pythoninfo:
os.uname: posix.uname_result(sysname='FreeBSD', nodename='123-RELEASE-p2-amd64-9e36', release='12.3-RELEASE-p1', version='FreeBSD 12.3-RELEASE-p1 GENERIC', machine='amd64')
The problem is that `/usr/include/sys/cdefs.hsets the ISO C standard to something older than-std=c11`` command line.
Reproducer, the 4 defines are copied from Python pyconfig.h:
#define _POSIX_C_SOURCE 200809L
#define _XOPEN_SOURCE 700
#define _XOPEN_SOURCE_EXTENDED 1
#define __BSD_VISIBLE 1
#include <assert.h>
int main()
{
static_assert(1 == 1, "ok");
static_assert(1 == 0, "bug");
return 0;
}- _XOPEN_SOURCE=700 sets _POSIX_C_SOURCE to 200809
- _POSIX_C_SOURCE=200809 sets __ISO_C_VISIBLE to 1999
- <assert.h> does not define static_assert() if __ISO_C_VISIBLE is less than 2011 which is the case here!
In <sys/cdefs.h>, I don't see any value of _XOPEN_SOURCE or _POSIX_C_SOURCE which could give a C standard higher than 2008. It seems like _XOPEN_SOURCE and _POSIX_C_SOURCE should not be defined to get ISO C11 (which defines static_assert()).
But the Python build system is complex, and I'm not comfortable to remove _XOPEN_SOURCE and _POSIX_C_SOURCE from pyconfig.h on all BSD platforms. I don't know if it would drop support for old FreeBSD version or if it would break other BSD variants like OpenBSD and NetBSD.
An alternative would be to use _Static_assert(). It should work, but I like static_assert() syntax, and we may use other C11 features
tomorrow.
Another alternative is to define static_assert() in Python if it's not defined... but I dislike working around issues with system headers :-(