Re: [patch] libstdc++/67173 Fix filesystem::canonical for Solaris 10.

[Jonathan Wakely <jwakely at redhat dot com>]

On 16/09/15 15:42 +0100, Jonathan Wakely wrote:
> @@ -22,6 +22,8 @@
> // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
> // <http://www.gnu.org/licenses/>.
>
> +#define _XOPEN_SOURCE 700
> +
> #include <experimental/filesystem>
> #include <functional>
> #include <stack>

Unfortunately this completely breaks NetBSD, because defining
_XOPEN_SOURCE for this one file is inconsistent with how the autconf
test were run, so C99 functions that were implicitly available during
configure tests (because no _POSIX_C_SOURCE, _XOPEN_SOURCE etc. macro
was defined) are no longer available when compiling this translation
unit with _XOPEN_SOURCE defined.

Specifically, <wchar.h> in NetBSD 5.1 does:

#if !defined(_ANSI_SOURCE) && !defined(_POSIX_C_SOURCE) && \
   !defined(_XOPEN_SOURCE) && !defined(_NETBSD_SOURCE)
#define _NETBSD_SOURCE 1
#endif
...
#if defined(_ISOC99_SOURCE) || (__STDC_VERSION__ - 0) > 199901L || \
   defined(_NETBSD_SOURCE)
int vfwscanf(FILE * __restrict, const wchar_t * __restrict, _BSD_VA_LIST_);


So it's defined during configure and we define _GLIBCXX_HAVE_VFWSCANF
and our <cwchar> does:

#if _GLIBCXX_HAVE_VFWSCANF
 using ::vfwscanf;
#endif

but the value of _GLIBCXX_HAVE_VFWSCANF determined during configure is
not valid in src/filesystem/ops.cc after defining _XOPEN_SOURCE.

I don't know how to use _XOPEN_VERSION or _POSIX_VERSION to check for
a suitable realpath without defining one of those feature-test macros,
which then breaks other things.

(This is fixed in NetBSD 7.x which knows about C++11 and so defines
vfwscanf more liberally, but that doesn't help NetBSD 5.1).

Maybe I should just give up on realpath() and use my new
implementation everywhere :-(