[libcxx] Set _LIBCPP_ELAST for mingw.

[danalbert]

Normally wouldn't bother with a review for something so trivial, but I know close to nothing about mingw, so I'm hoping someone can tell me if this is right. AIUI, mingw should emulate Linux, so that's what I've done here.

[EricWF]

I have a mingw environment set up so I'll test this and look into it tomorrow.

[mclow.lists]

I, too, know pretty much nothing about mingw. but structurally, this looks fine to me.

[majnemer]

I don't think it makes sense to use 4095, that number comes from Linux's kernel-user space ABI. MinGW targets link against the MSVC runtime, we should use _sys_nerr.

[danalbert]

Use _sys_nerr at David's suggestion.

[danalbert]

Thanks, figured you might know yet forgot to add you as a reviewer...

[EricWF]

_sys_nerr seems to be the correct value but it is not available in <__config>. In my mingw setup the definition is located in <stdlib.h>, so an include needs to be added.

[mclow.lists]

I'm reluctant to add yet another include into <__config>.
It includes too much stuff already.

[jroelofs]

can it be forward declared?

[EricWF]

_LIBCPP_ELAST is sparsely used, and it already drags in <errno.h>. I think we should just find a new place for it to live.
It's only used in src/system_error.cpp and src/ios.cpp so it doesn't even have to live in the headers.

[danalbert]

Factor ELAST configuration out into src/config_elast.h.
Use _WIN32 instead of MINGW32 since this is true for MSVC as well.

[danalbert]

Fix file name in file header.

[mclow.lists]

Other than that - this looks good to me.

Has anyone tried this on FreeBSD?

src/system_error.cpp

11 ↗

(On Diff #17200)

Please always include <__config> first.

This is a convention, rather than a requirement, since the first thing that <system_error> does is include <__config>

[danalbert]

Move __config inclusion back to the top of the list.

[EricWF]

LGTM.

include/__config

 
 #if defined(ELAST)
 #define _LIBCPP_ELAST ELAST
 #elif defined(__linux__)
 #define _LIBCPP_ELAST 4095
 #elif defined(_NEWLIB_VERSION)
 #define _LIBCPP_ELAST __ELASTERROR
 #elif defined(__APPLE__)
-// Not _LIBCPP_ELAST needed on Apple
+// No _LIBCPP_ELAST needed on Apple
 #elif defined(__sun__)
 #define _LIBCPP_ELAST ESTALE
+#elif defined(__MINGW32__)
+#define _LIBCPP_ELAST _sys_nerr
 #else
 // Warn here so that the person doing the libcxx port has an easier time:
 #warning This platform's ELAST hasn't been ported yet
 #endif
 
 #ifndef _LIBCPP_TRIVIAL_PAIR_COPY_CTOR
 #  define _LIBCPP_TRIVIAL_PAIR_COPY_CTOR 1
 #endif