[swift-evolution] [swift-dev] [Compiler] Help IR gen in targetting MSVC

[Joe Groff]

> On Apr 26, 2016, at 1:24 PM, John McCall via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> On Apr 26, 2016, at 1:03 PM, Sangjin Han <tinysun.net at gmail.com> wrote:
>> The problem can be solved by modifying that code. Thanks you. I thought that code will affect only to the CLong type not Int.
> 
> It changes what 'long' gets imported as.  If there's a Windows API defined using 'long' (rather than some more meaningful typedef like 'size_t'), it's important for it to be imported as Int32 rather than Int, since 'long' is always 32 bits under MSVC.
> 
>> But I meet another problem to fix it. I couldn't find the conditional method to distinct x86_64-*-windows-msvc with x86_64-*-windows-cygnus in Swift source.
>> 
>> "#if os(Windows)" can not distinct MSVC from Cygwin.
>> 
>> Should I add new condition 'env()' for the environment?
> 
> That is an excellent question.
> 
> My understanding / memory is that, as far as their programming interfaces goes, Cygwin and MSVC are very, very different environments.  Maybe it's useful to have a condition that's true for both environments — although I'm not sure why it would — but I don't think it deserves to be as prominent as os(Windows).  So my gut reaction is that, rather than adding a #env, we ought to just reserve os(Windows) for MSVC compatibility and make a new os(Cygwin) for Cygwin.
> 
> This needs to be raised on swift-evolution, though.  CC'ing that list.

It's an interesting question. Mingw, Cygwin, and MSVC definitely vary greatly in ABI and C language level behavior, but the underlying Win32 system libraries remain the same. I think it makes sense to consider them different os(...) environments, but it would also make sense IMO to have a broader platform check for Win32. Along similar lines, Linux, FreeBSD, and Darwin are different OSes, but all also share a POSIX environment.

-Joe