Re: [PATCH][_GLIBCXX_INLINE_VERSION] Fix <format> friend declarations

[Jonathan Wakely <jwakely@redhat.com>]

On Tue, 12 Sept 2023 at 17:47, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> On Wed, 23 Aug 2023 at 18:35, François Dumont via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > Hi
> >
> > The few tests that are failing in versioned namespace mode are due to
> > those friend declarations.
> >
> > This is a fix proposal even if I considered 2 other options:
> >
> > 1. Make __format::_Arg_store a struct and so do not bother with friend
> > declarations.
> >
> > 2. Consider it as a compiler bug and do nothing. In this case I think we
> > might still need this patch to avoid a non-working format library in
> > versioned namespace mode in gcc 14 if compiler bug is not fixed.
>
> It definitely is a compiler bug, this is PR c++/59256.
>
> Please add a comment to the new macro definition, so we remember to
> remove it when it's not needed:
>
>
> #if _GLIBCXX_INLINE_VERSION
> // Needed because of PR c++/59526
> # define _GLIBCXX_STD_V std::__8
> #else
> # define _GLIBCXX_STD_V std
> #endif
>
>
> OK with that change, thanks.

Actually, are you sure the friend std::basic_format_args declaration
needs to change?

I only see errors for the friend function, not the friend class. So
this seems to fix it:

--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -3437,7 +3437,13 @@ namespace __format

      template<typename _Ctx, typename... _Argz>
       friend auto
-       std::make_format_args(_Argz&&...) noexcept;
+#if _GLIBCXX_INLINE_VERSION
+       // Needed for PR c++/59526
+       std::__8::
+#else
+       std::
+#endif
+       make_format_args(_Argz&&...) noexcept;

      // For a sufficiently small number of arguments we only store values.
      // basic_format_args can get the types from the _Args pack.




>
>
> >
> > I can also define _GLIBCXX_STD_V at <format> level to limit impact.
> >
> >      libstdc++: [_GLIBCXX_INLINE_VERSION] Fix <format> friend declarations
> >
> >      GCC do not consider the inline namespace in friend declarations. We
> > need
> >      to explicit this namespace.
> >
> >      libstdc++-v3/ChangeLog:
> >
> >              * include/bits/c++config (_GLIBCXX_STD_V): New macro giving
> > current
> >              std namespace with optionally the version namespace.
> >              * include/std/format (std::__format::_Arg_store): Use
> > latter on friend
> >              declarations.
> >
> > Tested under versioned mode.
> >
> > Ok to commit ?
> >
> > François