I was a little bit too confident below. After review of all _M_singular 
usages I found another necessary fix.

After this one for sure we will be able to define 
__cpp_lib_null_iterators even in Debug mode.

     libstdc++: Fix N3344 behavior on _Safe_iterator::_M_can_advance

     We shall be able to advance from a 0 offset a value-initialized 
iterator.

     libstdc++-v3/ChangeLog:

             * include/debug/safe_iterator.tcc 
(_Safe_iterator<>::_M_can_advance):
             Accept 0 offset advance on value-initialized iterator.
             * testsuite/23_containers/vector/debug/n3644.cc: New test case.

Ok to commit ?

François


On 17/03/2024 17:52, François Dumont wrote:
>
>>
>> OK for trunk, thanks!
>>
>> I think this is OK to backport to 13 too.
>>
>> Maybe after this we can define the __cpp_lib_null_itetators macro for 
>> debug mode?
>>
> After this fix of local_iterator I think we can indeed.
>
> In fact the added 11316.cc was already passing for 
> unordered_set<>::local_iterator but simply because we were missing the 
> singular check. Both issues solved with this patch.
>
> I found the version.def file to cleanup but no idea how to regenerate 
> version.h from it so I'll let you do it, ok ?
>
>     libstdc++: Fix _Safe_local_iterator<>::_M_valid_range
>
>     Unordered container local_iterator range shall not contain any 
> singular
>     iterator unless both iterators are value-initialized.
>
>     libstdc++-v3/ChangeLog:
>
>             * include/debug/safe_local_iterator.tcc
>             (_Safe_local_iterator::_M_valid_range): Add 
> _M_value_initialized and
>             _M_singular checks.
>             * testsuite/23_containers/unordered_set/debug/114316.cc: 
> New test case.
>
>
> Ok to commit ?
>
> François