[PATCH] Use _GLIBCXX_NOEXCEPT_IF for std::swap

[Stephan Bergmann]

On 29/04/2019 15:26, Jonathan Wakely wrote:
>  Â Â Â Â * include/bits/move.h (swap(T&, T&), swap(T (&)[N], T (&)[N])): Use
>  Â Â Â Â _GLIBCXX_NOEXCEPT_IF to simplify declarations.
> 
> This just avoids having to repeat the name and parameter-list of the
> functions.

libstdc++-v3/include/std/type_traits still has

>   template<typename _Tp>
>     inline
>     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
> 			      is_move_constructible<_Tp>,
> 			      is_move_assignable<_Tp>>::value>::type
>     swap(_Tp&, _Tp&)
>     noexcept(__and_<is_nothrow_move_constructible<_Tp>,
> 	            is_nothrow_move_assignable<_Tp>>::value);

using noexcept instead of _GLIBCXX_NOEXPECT_IF, and at least during 
configure of building LibreOffice with Clang, that causes failure

> .../gcc/trunk/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/bits/move.h:185:5: error: exception specification in declaration does not match previous declaration
>     swap(_Tp& __a, _Tp& __b)
>     ^
> .../gcc/trunk/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/type_traits:2531:5: note: previous declaration is here
>     swap(_Tp&, _Tp&)
>     ^

I didn't try to track down under what conditions _GLIBCXX_NOEXCEPT_IF 
would not expand to noexcept, but I assume that just type_traits needs 
adapting, too?