[vlc-devel] [PATCH] configure: Check the toolchain default _WIN32_WINNT in addition to a command line override

[Martin Storsjö]

On Fri, 3 Apr 2020, Steve Lhomme wrote:

> On 2020-04-03 13:27, Martin Storsjö wrote:
>> Since 255e2ce27, we try not to override _WIN32_WINNT in case it already
>> is defined on the command line to a higher value. However, if it isn't
>> specified on the command line, but the toolchain headers default to
>> a newer version, we should also honor it and keep that version instead
>> of forcing a lower version here. (If the toolchain defaults to a newer
>> version, runtime libs of the toolchain may rely on such a new version
>> anyway, so forcing a lower target within VLC might be useless.)
>
> This seems OK although it may create issues with code like this:
> #ifdef HAVE_CONFIG_H
> # include "config.h"
> #endif
>
> #if !defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0601 // _WIN32_WINNT_WIN7
> # undef _WIN32_WINNT
> # define _WIN32_WINNT 0x0601 // _WIN32_WINNT_WIN7
> #endif

>
> In this case the user may not set value in the command-line and the 
> default one from the toolchain is used. But it may be higher than Win7 
> but then we force it down.

Hmm, you're right...

To handle that case gracefully, we would either need to include _mingw.h 
(which sets such defaults, if __MINGW32__ is defined) between config.h and 
the _WIN32_WINNT adjustment, or try to parse out the toolchain default 
value in configure and set that in config.h, instead of the VLC default.

> On the other hand it's not a regression. In that case we use to set the 
> value in config.h to Win7 and it would never pick the default toolchain 
> one. But we need to keep this in mind. Especially when backporting to 
> 3.0 (because win7 is a bad example since that's the minimum in 4.0 anyway).

Well this is only an issue for the specific source files where we override 
the common version, right?

> I'm OK with the change if we decide we don't want people to compile 4.0 
> for anything lower than Win7.

I don't see how this patch is an issue for that particular case though. If 
you intentionally want to compile for a lower version, pass 
-D_WIN32_WINNT=0x0600 in CFLAGS/CXXFLAGS, then it will always be defined 
and used, except for the few source files where we force a custom value - 
but those files where we force a custom value is where we normally use 
GetProcAddress() and similar things anyway, right?

// Martin