Build Python with C11

[vstinner]

PEP 7 was recently updated to require a C11 compiler (without optional features) to build Python. I propose to now implement this new requirement:

• Build Python with -std=c11 rather than -std=c99
• Use static_assert() of <assert.h>

It's already documented in What's New in Python 3.11:

Building Python now requires a C11 compiler without optional C11 features. (Contributed by Victor Stinner in bpo-46656.

https://docs.python.org/dev/whatsnew/3.11.html#build-changes

• PR: gh-99069: Consolidate checks for static_assert #94766

[corona10]

+1

[vstinner]

I merged 2 PRs:

• gh-91731: Build Python with -std=c11 #91733
• gh-91731: Replace Py_BUILD_ASSERT() with static_assert() #91730

I close the issue.

[gvanrossum]

What about Windows? @zooba are we already building with C11 there?

[zooba]

What about Windows? @zooba are we already building with C11 there?

Apparently, or CI would have broken. I guess we'll find out when people start using new language features.

[vstinner]

What about Windows? @zooba are we already building with C11 there?

When the PEP 7 change was discussed on python-dev, it was said that MSVC supports C11 without optional features.

• https://mail.python.org/archives/list/python-dev@python.org/thread/J5FSP6J4EITPY5C2UJI7HSL2GQCTCUWN/
• https://devblogs.microsoft.com/cppblog/c11-and-c17-standard-support-arriving-in-msvc/ <= mentions _Static_assert and has an example using static_assert() of <assert.h>

My PR got merged and the CI is fine. Do you have remaining concerns about MSVC?

The blog post mentions the /std:c11 option: https://docs.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=msvc-170 It doesn't seem to be used by Python currently.

I only these /std options:

PCbuild/python_uwp.vcxproj:93:      <AdditionalOptions>/EHsc /std:c++17 %(AdditionalOptions)</AdditionalOptions>
PCbuild/pythonw_uwp.vcxproj:93:      <AdditionalOptions>/EHsc /std:c++17 %(AdditionalOptions)</AdditionalOptions>

The blog post also mentions the /Zc:preprocessor option to switch the preprocessor to C11 mode ("conformant preprocessor"): https://docs.microsoft.com/en-us/cpp/build/reference/zc-preprocessor?view=msvc-170 This option doesn't seem to be currently used by Python.

[gvanrossum]

My remaining concern is that I tried to use static_assert() in #32387 and it broke on Windows. I've merged the latest main and it still breaks. I'll just assume that that is a different problem so I'll move on. (If you want to look into it, details are in that issue.)

[zooba]

The blog post mentions the /std:c11 option: https://docs.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=msvc-170 It doesn't seem to be used by Python currently.

Yeah, this probably needs to be added (in pyproject.props). I don't think it will matter if it's included twice in the C++ projects, but that would be the biggest issue.

[gvanrossum]

I reopen the issue.