Re: [PATCH 8/9] meson: fix compilation with Visual Studio

> The Visual Studio compiler defaults to C89 unless explicitly asked to
> use a different version of the C standard. We don't specify any C
> standard at all though in our Meson build, and consequently compiling
> Git fails:
> 
>      ...\git\git-compat-util.h(14): fatal error C1189: #error:  "Required C99 support is in a test phase.  Please see git-compat-util.h for more details."
> 
> Fix the issue by specifying the project's C standard. Funny enough,
> specifying C99 does not work because apparently, `__STDC_VERSION__` is
> not getting defined in that version at all. Instead, we have to specify
> C11 as the project's C standard, which is also done in our CMake build
> instructions.
> 
> We don't want to generally enforce C11 though, as our requiremets only
> state that a C99 compiler is required. In fact, we don't even require
> plain C99, but rather the GNU variant thereof.
> 
> Meson allows us to handle this case rather easily by specifying
> "gnu99,c11", which will cause it to fall back to C11 in case GNU C99 is
> unsupported. This feature has only been introduced with Meson 1.3.0
> though, and we support 0.61.0 and newer. In case we use such an oldish
> version though we fall back to requiring GNU99 unconditionally. This
> means that Windows essentially requires Meson 1.3.0 and newer when using
> Visual Studio, but I doubt that this is ever going to be a real problem.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>

> ---
>   meson.build | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index cb352ce6fd50616e3281a776104692c5b2bfa5b2..831da1d43cafe85a8c9ac872e141476adbc08188 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -171,6 +171,14 @@
>   project('git', 'c',
>     meson_version: '>=0.61.0',
>     version: files('GIT-VERSION'),
> +  default_options: [
> +    # Git requires C99 with GNU extensions, which of course isn't supported by
> +    # MSVC. Funny enough, C99 doesn't work with MSVC either, as it has only
> +    # learned to define __STDC_VERSION__ with C11 and later. We thus require
> +    # GNU C99 and fall back to C11. Meson only learned to handle the fallback
> +    # with version 1.3.0, so on older versions we use GNU C99 unconditionally.
> +    'c_std=' + (meson.version().version_compare('>=1.3.0') ? 'gnu99,c11' : 'gnu99'),
> +  ]
>   )
>   
>   fs = import('fs')
>