Microsoft's C language policy (was: [PATCH 0/1] Add a test balloon for C99)

On Sun, Nov 14 2021, brian m. carlson wrote:

[Replying to this tidbit in the v1 CL, which isn't in the V2 one]

Unfortunately, Microsoft for many years refused[1] to support C99 in
MSVC, and still does not officially do so.  However, they recently added
support for C11 and C17, which are sufficient for modern programming.
These require a newer version of MSVC, including an updated SDK.  The
SDK update is available for download free of charge, and most public CI
systems have support for both the updated MSVC and the SDK update.

Even for users who would like to target an older version of Windows,
such as the no longer supported Windows 7, GCC and Clang are available.
The LLVM suite, including Clang, is available pre-compiled for download
free of charge.  Using a different compiler is specifically proposed by
Microsoft staff[1] as a solution for users who wish to build modern
programs for MSVC versions which do not support modern C.

As such, we can assume that Git can be safely compiled with C99 or C11
support on all operating systems which receive security support, and
even some which do not.  Our CI confirms that this series passes all
tests.  Let's introduce a test balloon which checks for this support and
fails with an error message if it is absent.

[0] The reader will note that there are people working professionally in
this industry who were not yet born at the time C99 was ratified.  Thus,
this occurred quite a long time ago indeed.
[1] https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-and-c99/

I hadn't seen that blog post before I'd read it when going over your
series. I'd assumed that Microsoft was just dragging their feed on C
language support, but that post indicates (from what seems to be as
official of a source as anyone's going to get) that they're intending to
not support C at all, but just some pseudo-C that happens to be a
convenient subset of C++.

However that post is from 2012, and you indicate that they've since
added (full?) support for C11 and C17.

So is this "policy" of supporting some arbitrary subset of C++ at all
current as far as MSVC today goes?

Aside: I just remembered we had a (seemingly abandoned) effort to get git's sources to
compile with a C++ compiler[1], which would be another possible way
forward to using more modern C features that happened to overlap with
C++. Another one would be some sort of coccinelle-powered refactoring or
other source pre-processing...

1. https://lore.kernel.org/git/20180129223728.30569-1-bmwill@google.com/ (local)