[boost] [winapi] Problem with the latest clang on Windows

Subject: [boost] [winapi] Problem with the latest clang on Windows
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-05-31 20:07:43

Updates to clang on Windows have broken the use of clang with the 
[winapi] library. I do not know if this has occurred in the past but it 
seems to have occurred recently when I build the latest clang from 
source and use it on Windows to compile build Boost libraries which use 
the internal winapi library.

Preprocessing clang and gcc output for a given call in the Boost winapi 
library and in the corresponding mingw windows.h shows that both 
compilers view the same source but treat them differently.

As an example let's look at the GetSystemTimeAsFileTime call. The 
preprocessed source for both clang and gcc shows:

In the Boost winapi it is:

      __attribute__((dllimport)) void __attribute__((__stdcall__))
          GetSystemTimeAsFileTime(FILETIME_* lpFileTime);

In the mingw/gcc windows.h it is:

      void __attribute__((__stdcall__)) GetSystemTimeAsFileTime(LPFILETIME);

where the FILETIME_ and LPFILETIME are the same.

When gcc sees these two declarations in the two different headers it 
says everything is OK.

When clang sees these two declarations in the two different headers it 
gives an error:

In file included from test_winapi.cpp:9:
In file included from /mingw/include\windows.h:62:
/mingw/include\winbase.h:1397:24: error: conflicting types for 
'GetSystemTimeAsFileTime'
WINBASEAPI void WINAPI GetSystemTimeAsFileTime(LPFILETIME);
                        ^
..\..\..\boost/detail/winapi/time.hpp:70:9: note: previous declaration 
is here
         GetSystemTimeAsFileTime(FILETIME_* lpFileTime);
         ^

For this line in boost/detail/winapi/time.hpp

     __declspec(dllimport) void WINAPI
         GetSystemTimeAsFileTime(FILETIME_* lpFileTime);

It seems like the fix for clang is to leave out the 
__declspec(dllimport) portion of all these Boost winapi calls while 
leaving it in for everybody else. I am discussing this on the clang 
developers mailing list but it seems like they are pretty adamant that 
if they see __attribute__((dllimport)) in from of a function declaration 
and do not see it in front of another function declaration, despite the 
rest of the signatire being the same, the two declarations are not the 
same function being declared and therefore an error because of ODR.