Error C2467 when "Disable Language Extensions" is set to "Yes (/Za)" in MSVC 16.8

[mw4853]

Visual Studio 2019 v16.8 reports the following error on this line if you include <boost/chrono.hpp> in a Win32 project:

boost-1.74\boost\winapi\basic_types.hpp(255,6): error C2467: illegal declaration of anonymous 'struct'

https://github.com/boostorg/winapi/blob/37607cc3d3ea5145381f65b6fe51eac8bb8f361f/include/boost/winapi/basic_types.hpp#L255

For this .vcxproj, I do have "Disable Language Extensions" set to "Yes (/Za)", which seems to be triggering this issue. Also: "C++ Language Standard" is set to "Default (ISO C++14 Standard)" "C Language Standard" is set to "Default (Legacy MSVC)"

[mw4853]

It looks like something like this is necessary (from winnt.h, Windows 10 SDK 10.0.18362.0):

typedef union _LARGE_INTEGER {
    struct {
        DWORD LowPart;
        LONG HighPart;
    } DUMMYSTRUCTNAME;
    struct {
        DWORD LowPart;
        LONG HighPart;
    } u;
    LONGLONG QuadPart;
} LARGE_INTEGER;

Elsewhere in winnt.h:

#ifndef DUMMYSTRUCTNAME
#if defined(NONAMELESSUNION) || !defined(_MSC_EXTENSIONS)
#define DUMMYSTRUCTNAME  s
#define DUMMYSTRUCTNAME2 s2
#define DUMMYSTRUCTNAME3 s3
#define DUMMYSTRUCTNAME4 s4
#define DUMMYSTRUCTNAME5 s5
#define DUMMYSTRUCTNAME6 s6
#else
#define DUMMYSTRUCTNAME
#define DUMMYSTRUCTNAME2
#define DUMMYSTRUCTNAME3
#define DUMMYSTRUCTNAME4
#define DUMMYSTRUCTNAME5
#define DUMMYSTRUCTNAME6
#endif
#endif // DUMMYSTRUCTNAME

There is some information about DUMMYSTRUCTNAME here: https://devblogs.microsoft.com/oldnewthing/20170907-00/?p=96956

[Lastique]

I think it's too late to implement support for /Za in 1.75, so my suggestion for now is to compile with extensions enabled. I'll see what can be done past 1.75.

[walbourn]

/Za is deprecated in MSVC, and it reflects a really old ANSI version.

The modern MSVC 'conformance' switches are:

/permissive- /Zc:__cplusplus /Zc:inline
/Zc:preprocessor // 19.26 or later
/Zc:lambda // 19.28 or later
/Zc:templateScope // 19.35 or later