Re: [PATCH] libstdc++: Implement LWG 3470 change to ranges::subrange

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

On Tue, 19 Oct 2021, 19:30 Patrick Palka via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> Tested on x86_64-pc-linux-gnu, does this look OK for trunk and branches?
>

Yes, thanks.


> libstdc++-v3/ChangeLog:
>
>         * include/bits/ranges_util.h
>         (__detail::__uses_nonqualification_pointer_conversion): Define
>         and use it ...
>         (__convertible_to_nonslicing): ... here, as per LWG 3470.
>         * testsuite/std/ranges/subrange/1.cc: New test.
> ---
>  libstdc++-v3/include/bits/ranges_util.h       | 13 +++++++++----
>  .../testsuite/std/ranges/subrange/1.cc        | 19 +++++++++++++++++++
>  2 files changed, 28 insertions(+), 4 deletions(-)
>  create mode 100644 libstdc++-v3/testsuite/std/ranges/subrange/1.cc
>
> diff --git a/libstdc++-v3/include/bits/ranges_util.h
> b/libstdc++-v3/include/bits/ranges_util.h
> index 7e7b958d274..765848e327d 100644
> --- a/libstdc++-v3/include/bits/ranges_util.h
> +++ b/libstdc++-v3/include/bits/ranges_util.h
> @@ -184,11 +184,16 @@ namespace ranges
>
>    namespace __detail
>    {
> -    template<class _From, class _To>
> +    template<typename _From, typename _To>
> +      concept __uses_nonqualification_pointer_conversion
> +       = is_pointer_v<_From> && is_pointer_v<_To>
> +         && !convertible_to<remove_pointer_t<_From>(*)[],
> +                            remove_pointer_t<_To>(*)[]>;
> +
> +    template<typename _From, typename _To>
>        concept __convertible_to_non_slicing = convertible_to<_From, _To>
> -       && !(is_pointer_v<decay_t<_From>> && is_pointer_v<decay_t<_To>>
> -           && __different_from<remove_pointer_t<decay_t<_From>>,
> -                               remove_pointer_t<decay_t<_To>>>);
> +       && !__uses_nonqualification_pointer_conversion<decay_t<_From>,
> +                                                      decay_t<_To>>;
>
>      template<typename _Tp>
>        concept __pair_like
> diff --git a/libstdc++-v3/testsuite/std/ranges/subrange/1.cc
> b/libstdc++-v3/testsuite/std/ranges/subrange/1.cc
> new file mode 100644
> index 00000000000..8a53261c78c
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/std/ranges/subrange/1.cc
> @@ -0,0 +1,19 @@
> +// { dg-options "-std=gnu++20" }
> +// { dg-do run { target c++20 } }
> +
> +#include <ranges>
> +
> +void
> +test01()
> +{
> +  // LWG 3470
> +  int a[3] = {1,2,3};
> +  int* b[3] = {&a[2], &a[0], &a[1]};
> +  auto c = std::ranges::subrange<const int*const*>(b);
> +}
> +
> +int
> +main()
> +{
> +  test01();
> +}
> --
> 2.33.1.711.g9d530dc002
>
>