[PATCH] Use _GLIBCXX_NOEXCEPT_IF for std::swap

[Jonathan Wakely]

On 02/05/19 21:33 +0100, Jonathan Wakely wrote:
>On 02/05/19 20:11 +0100, Jonathan Wakely wrote:
>>On 02/05/19 20:09 +0100, Jonathan Wakely wrote:
>>>On 02/05/19 20:34 +0200, Stephan Bergmann wrote:
>>>>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?
>>>
>>>That's weird. _GLIBCXX_NOEXCEPT_IF is only empty for C++11, in which
>>>case the declaration in <type_traits> isn't seen anyway. And there's
>>>no point using _GLIBCXX_NOEXCEPT_IF in <type_traits> because we can
>>>(and should) just use noexcept directly in C++11 code. The macro
>>>exists for code that needs to be compiled as C++98 too.
>>>
>>>The only difference is that there's an extra set of parentheses around
>>>the NOEXCEPT_IF condition, so the preprocessor doesn't try to eat the
>>>comma.
>>>
>>>So one declaration is:
>>>
>>>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);
>>>
>>>And the other is:
>>>
>>>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));
>>
>>Yep, Clang doesn't like that:
>>https://wandbox.org/permlink/clslE9PGCVtKPppz
>
>This was also reported as https://gcc.gnu.org/PR90314

And here's what I've tested and committed.


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