[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 13:57, Martin Storsjö wrote:
>> 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.
>
> That would be nice but it sounds tricky.
> Or maybe using the output of such a program in the configure script:
>
> #include <windows.h>
> #include <stdio.h>
> int main(void) {
>   printf("0x%04X", _WIN32_WINNT);
>   return 0;
> }

Yeah, except we can't count on executing test apps - so it'd have to be 
something like "$CC -E | tail -1" on something like this:

#include <windows.h>
_WIN32_WINNT


>>> 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
>
> Ah yes, so it's only for toolchain that would have a default (but not 
> force via the command-line) version higher than Win7 where we might 
> benefit of new API. I don't know if that's possible in mingw64, like 
> when WINSTORECOMPAT is set. I don't think that's the case with MSVC.

Yes, it's possible - mingw-w64 normally default to 0x502, but it's 
settable when installing mingw-w64-headers 
(--with-default-win32-winnt=whatever) - llvm-mingw defaults to 0x0601.

So therefore I think one gets a more consistent experience if config.h 
doesn't force it to a lower version. On 4.0/master it's not an issue as it 
sets the same version as the toolchain, but the generic mechanism would be 
good for 3.0 I think, to avoid forcing 0x502 on llvm-mingw there.

// Martin