Re: [musl] Question on C++ locale

["Érico Nogueira" <ericonr@disroot.org>]

On Mon Nov 30, 2020 at 11:39 AM -03, Samuel Holland wrote:
> On 11/30/20 7:44 AM, Érico Nogueira wrote:
> > On Mon Nov 30, 2020 at 8:35 AM -03, Szabolcs Nagy wrote:
> >> * Dong Brett <brett.browning.dong@gmail.com> [2020-11-30 18:41:33
> >> +0800]:
> >>> However, the following C++ code does not work (our software uses std::locale in C++ standard library for locale related stuff):
> >>> #include <langinfo.h>
> >>> #include <locale.h>
> >>> #include <locale>
> >>> using namespace std;
> >>> int main()
> >>> {
> >>>     std::locale::global(locale(""));
> >>>     initscr();
> >>>     printw("LC_ALL: %s\n", setlocale(LC_ALL, NULL));
> >>>     printw("C++ locale: %s\n", locale().name().c_str());
> >>>     printw("CODESET: %s\n", nl_langinfo(CODESET));
> >>>     printw("Hello, world!\n");
> >>>     printw("你好，世界!\n");
> >>>     refresh();
> >>>     getch();
> >>>     endwin();
> >>>     return 0;
> >>> }
> >>
> >> fwiw for me even the first line fails.
> >> i don't know how c++ locales are supposed to work.
> > 
> > From [1], it seems that C++ locales are supposed to affect the global
> > locale as well, so they should call setlocale() when appropriate.
> > 
> > - [1] https://www.cplusplus.com/reference/locale/locale/
> > 
> > Unfortunately, I assume libstdc++ uses their generic locale support on
> > musl...  From gcc-10.2.0/libstdc++-v3/config/locale/generic/c_locale.cc:
> > 
> >   void
> >   locale::facet::_S_create_c_locale(__c_locale& __cloc, const char* __s,
> > 				    __c_locale)
> >   {
> >     // Currently, the generic model only supports the "C" locale.
> >     // See http://gcc.gnu.org/ml/libstdc++/2003-02/msg00345.html
> >     __cloc = 0;
> >     if (strcmp(__s, "C"))
> >       __throw_runtime_error(__N("locale::facet::_S_create_c_locale "
> > 			    "name not valid"));
> >   }
> > 
>
> I don't know for sure that it's the right thing to do, but I have been
> patching
> out that error for the last several years[1] and so far I have not
> noticed any
> negative effects. Adelie, which is very thorough about testing, has also
> carried
> the patch for a while[2].
>
> Samuel
>
> [1]:
> https://github.com/smaeul/portage/blob/c744774a/patches/sys-devel/gcc/gcc-5.4.0-locale.patch
> [2]: https://code.foxkit.us/adelie/packages/-/commit/d09b437d

Are those patches correct in functionality? The GNU version is:

  void
  locale::facet::_S_create_c_locale(__c_locale& __cloc, const char* __s,
				    __c_locale __old)
  {
    __cloc = __newlocale(1 << LC_ALL, __s, __old);
    if (!__cloc)
      {
	// This named locale is not supported by the underlying OS.
	__throw_runtime_error(__N("locale::facet::_S_create_c_locale "
				  "name not valid"));
      }
  }

It tries to create a locale object, which the generic code doesn't do.
In the generic case, _S_create_c_locale is basically a noop, and I'd
assume localization wouldn't work, even if it does avoid the runtime
abort.

I will try it out locally when I get the time.