Re: [PATCH][_GLIBCXX_DEBUG] Fix std::__niter_base behavior

[Jonathan Wakely <jwakely.gcc@gmail.com>]

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On Mon, 19 Feb 2024, 08:12 Jonathan Wakely, <jwakely.gcc@gmail.com> wrote:

>
>
> On Mon, 19 Feb 2024, 07:08 Stephan Bergmann, <sberg.fun@gmail.com> wrote:
>
>> On 2/17/24 15:14, François Dumont wrote:
>> > Thanks for the link, tested and committed.
>>
>> I assume this is the cause for the below failure now,
>>
>
> Yes, the new >= C++11 overload of __niter_base recursively unwraps
> multiple layers of wrapping, so that a safe iterator wrapping a normal
> iterator wrapping a pointer is unwrapped to just a pointer. But then
> __niter_wrap doesn't restore both layers.
>


Actually that's not the problem. __niter_wrap would restore both layers,
except that it uses __niter_base itself:

>   347 |     { return __from + (__res - std::__niter_base(__from)); }
>       |                       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

And it seems to be getting called with the wrong types. Maybe that's just a
bug in std:: erase or maybe niter_wrap needs adjusting.

I'll check in a couple of hours if François doesn't get to it first.

I have to wonder how this wasn't caught by existing tests though.