[PATCH] libstdc++: fix inplace_vector deprecation warning

[Tomasz Kaminski]

On Fri, Sep 11, 2026 at 7:54 AM Tomasz Kaminski <tkaminsk@redhat.com> wrote:

>
>
>
> On Thu, Sep 10, 2026 at 10:57 PM Avi Kivity <avi@lists.scylladb.com>
> wrote:
>
>> From: Avi Kivity <avi@scylladb.com>
>>
>> Practically anything that touches std::inplace_vector causes
>> this warning to be generated:
>>
>> /usr/lib/gcc/x86_64-redhat-linux/16/../../../../include/c++/16/inplace_vector:853:20:
>> warning: 'is_trivial_v<unsigned int>' is deprecated: use
>> 'is_trivially_default_constructible_v && is_trivially_copyable_v' instead
>> [-Wdeprecated-declarations]
>>
> I will remove the path, leaving only inplace_vector to reduce this already
> long line.
>
>>   853 |             if constexpr (is_trivial_v<_Tp>)
>>       |                           ^
>> /usr/lib/gcc/x86_64-redhat-linux/16/../../../../include/c++/16/inplace_vector:128:2:
>> note: in instantiation of member function 'std::inplace_vector<unsigned
>> int, 2>::_M_init' requested here
>>   128 |         _M_init();
>>       |         ^
>>
>> Fix it by following the warning's recommendation.
>>
>>         PR libstdc++/127325
>>
>> libstdc++-v3/ChangeLog:
>>
>>         * include/std/inplace_vector: replace is_trivial_v with
>>         is_trivially_default_constructible_v and is_trivially_copyable_v.
>>
>> Signed-off-by: Avi Kivity <avi@scylladb.com>
>>
>> ---
>> DisclAImer: I bravely typed this in on my own.
>
> Thanks, as this is obvious fix, I will merge that to master and backport
> to 16.
>
Patch merged to both. Thank you for reporting it and fix.

>
>>  libstdc++-v3/include/std/inplace_vector | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/libstdc++-v3/include/std/inplace_vector
>> b/libstdc++-v3/include/std/inplace_vector
>> index 6d67a740f21..a2b5f31be92 100644
>> --- a/libstdc++-v3/include/std/inplace_vector
>> +++ b/libstdc++-v3/include/std/inplace_vector
>> @@ -860,11 +860,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
>>  #endif
>>           }
>>         else
>>           {
>>             // TODO: use new(_M_elems) _Tp[_Nm]() once PR121068 is fixed
>> -           if constexpr (is_trivial_v<_Tp>)
>> +           if constexpr (is_trivially_default_constructible_v<_Tp>
>> +                           && is_trivially_copyable_v<_Tp>)
>>               for (size_t __i = 0; __i < _Nm; ++__i)
>>                 _M_elems[__i] = _Tp();
>>             else
>>               __builtin_unreachable(); // only trivial types are
>> supported at compile time
>>           }
>> --
>> 2.55.0
>>
>>
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