[PATCH] Fix gnu-versioned-namespace build

[Jonathan Wakely]

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.


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