I guess that as usual, we should use the "common denominator" of all
compilers supported by CPython. For example, if MSVC doesn't support a
feature, we should not use it in CPython.

In practice, it's easy to check if a feature is supported or not: we
have buildbots building Python at each commit. It was very common to
get a compilation error only on MSVC when a variable was defined in
the middle of a function. We are now using
-Werror=declaration-after-statement with GCC because of MSVC!

Maybe GCC has an option to ask for the subset of the C99 standard
compatible with MSVC? Something like "-std=c99 -pedantic"?

Note: I tried -pedantic, GCC emits a lot of warnings on code which
looks valid and/or is protected with #ifdef for features specific to
GCC like computed goto.

Victor

2016-06-07 21:45 GMT+02:00 Guido van Rossum <gvanrossum@gmail.com>:
> We should definitely keep supporting MSVC.
>
> --Guido (mobile)
>
> On Jun 7, 2016 12:39 PM, "Sturla Molden" <sturla.molden@gmail.com> wrote:
>>
>> Victor Stinner <victor.stinner@gmail.com> wrote:
>>
>> > Is it worth to support a compiler that in 2016 doesn't support the C
>> > standard released in 1999, 17 years ago?
>>
>> MSVC only supports C99 when its needed for C++11 or some MS extension to
>> C.
>>
>> Is it worth supporting MSVC? If not, we have Intel C, Clang and Cygwin GCC
>> are the viable options we have on Windows (and perhaps Embarcadero, but I
>> haven't used C++ builder for a very long time). Even MinGW does not fully
>> support C99, because it depends on Microsoft's CRT. If we think MSVC and
>> MinGW are worth supporting, we cannot just use C99 indiscriminantly.
>>
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