[PATCH] Fix gnu-versioned-namespace build

[Jonathan Wakely]

On 30/10/20 18:51 +0100, François Dumont wrote:
>On 30/10/20 2:37 pm, Jonathan Wakely wrote:
>>On 30/10/20 13:23 +0000, Jonathan Wakely wrote:
>>>On 30/10/20 13:59 +0100, François Dumont via Libstdc++ wrote:
>>>>The gnu-versioned-namespace build is broken.
>>>>
>>>>The fix in charconv/floating_from_chars.cc is quite trivial. I 
>>>>am not so sure about the fix in sstream-inst.cc.
>>>
>>>The change for src/c++20/sstream-inst.cc is OK to commit. It would
>>>probably be better to not build that file at all if the cxx11 ABI is
>>>not supported at all, but then the src/c++20 directory would be empty
>>>and I'm not sure if that would work. So just making the file empty is
>>>fine.
>>>
>>>The change for from_chars is not OK. With your change the <charconv>
>>>header doesn't declare those functions if included by a file using the
>>>old ABI. That's wrong, they should be declared unconditionally.
>>>
>>>I see two ways to fix it. Either make the declarations in the header
>>>depend on ! _GLIBCXX_INLINE_VERSION (so they're disabled for
>>>gnu-versioned namespace) or fix the code in floating_from_chars to not
>>>use a pmr::memory_resource for allocation in the versioned namespace
>>>build.
>>
>>Here's a patch for the second way.
>>
>>A third way to fix it would be to make basic_string work with C++
>>allocators, so that pmr::string is usable for the gnu-versioned
>>namespace.
>>
>>And the fourth would be to switch the versioned namespace to use the
>>new ABI unconditionally, instead of using the old ABI unconditionally.
>>
>>
>Can I commit this one once tested then ?

Yes please.

>I'll try to put the fourth way in place however.

N.B. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83077 tracks that.