[PATCH 4/5] libstdc++: Implement resolution of LWG 3478 as per P2210

[Jonathan Wakely]

On Thu, 17 Jun 2021 at 16:51, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> This implements the part of P2210R2 "Superior String Splitting" that
> resolves LWG 3478 for split_view (now named lazy_split_view).
>
> libstdc++-v3/ChangeLog:
>
>         * include/std/ranges (lazy_split_view::_OuterIter::__at_end):
>         Check _M_trailing_empty.
>         (lazy_split_view::_OuterIter::_M_trailing_empty): Define this
>         data member.
>         (lazy_split_view::_OuterIter::operator++): Set _M_trailing_empty
>         appropriately.
>         (lazy_split_view::_OuterIter::operator==): Compare
>         _M_trailing_empty.
>         * testsuite/std/ranges/adaptors/100479.cc (test03): Expect two
>         split parts instead of one.
>         * testsuite/std/ranges/adaptors/lazy_split.cc (test11): New test.

OK (for trunk only, I think).



> ---
>  libstdc++-v3/include/std/ranges               | 21 +++++++++++++++----
>  .../testsuite/std/ranges/adaptors/100479.cc   |  6 +++---
>  .../std/ranges/adaptors/lazy_split.cc         | 15 +++++++++++++
>  3 files changed, 35 insertions(+), 7 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index cc1ef112ff1..78562924bee 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -2879,7 +2879,7 @@ namespace views::__adaptor
>
>           constexpr bool
>           __at_end() const
> -         { return __current() == ranges::end(_M_parent->_M_base); }
> +         { return __current() == ranges::end(_M_parent->_M_base) && !_M_trailing_empty; }
>
>           // [range.lazy.split.outer] p1
>           //  Many of the following specifications refer to the notional member
> @@ -2909,6 +2909,7 @@ namespace views::__adaptor
>           [[no_unique_address]]
>             __detail::__maybe_present_t<forward_range<_Vp>,
>                                         iterator_t<_Base>> _M_current;
> +         bool _M_trailing_empty = false;
>
>         public:
>           using iterator_concept = conditional_t<forward_range<_Base>,
> @@ -2977,7 +2978,10 @@ namespace views::__adaptor
>             // 3505. lazy_split_view::outer-iterator::operator++ misspecified
>             const auto __end = ranges::end(_M_parent->_M_base);
>             if (__current() == __end)
> -             return *this;
> +             {
> +               _M_trailing_empty = false;
> +               return *this;
> +             }
>             const auto [__pbegin, __pend] = subrange{_M_parent->_M_pattern};
>             if (__pbegin == __pend)
>               ++__current();
> @@ -2986,7 +2990,11 @@ namespace views::__adaptor
>                 __current() = ranges::find(std::move(__current()), __end,
>                                            *__pbegin);
>                 if (__current() != __end)
> -                 ++__current();
> +                 {
> +                   ++__current();
> +                   if (__current() == __end)
> +                     _M_trailing_empty = true;
> +                 }
>               }
>             else
>               do
> @@ -2996,6 +3004,8 @@ namespace views::__adaptor
>                   if (__p == __pend)
>                     {
>                       __current() = __b;
> +                     if (__current() == __end)
> +                       _M_trailing_empty = true;
>                       break;
>                     }
>                 } while (++__current() != __end);
> @@ -3018,7 +3028,10 @@ namespace views::__adaptor
>           friend constexpr bool
>           operator==(const _OuterIter& __x, const _OuterIter& __y)
>             requires forward_range<_Base>
> -         { return __x._M_current == __y._M_current; }
> +         {
> +           return __x._M_current == __y._M_current
> +             && __x._M_trailing_empty == __y._M_trailing_empty;
> +         }
>
>           friend constexpr bool
>           operator==(const _OuterIter& __x, default_sentinel_t)
> diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc
> index 9899ff92c0b..b8c1e6f4f57 100644
> --- a/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc
> @@ -95,11 +95,11 @@ test03()
>      | views::drop_while([](auto) { return false; })
>      | views::filter([](auto) { return true; });
>    static_assert(ranges::forward_range<decltype(v)>);
> -  VERIFY( ranges::next(v.begin()) == v.end() );
> +  VERIFY( ranges::distance(v) == 2 );
>    auto w = v;
> -  VERIFY( ranges::next(w.begin()) == w.end() );
> +  VERIFY( ranges::distance(v) == 2 );
>    auto z = std::move(w);
> -  VERIFY( ranges::next(z.begin()) == z.end() );
> +  VERIFY( ranges::distance(v) == 2 );
>    return true;
>  }
>
> diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc
> index 12844525d86..133e9a7025b 100644
> --- a/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc
> @@ -193,6 +193,20 @@ test10()
>    VERIFY( ranges::equal(v, (std::string_view[]){"x", "x"}) );
>  }
>
> +void
> +test11()
> +{
> +  // LWG 3478
> +  static_assert(ranges::distance(views::lazy_split("text"sv, "text"sv)) == 2);
> +  static_assert(ranges::distance(views::lazy_split(" text "sv, ' ')) == 3);
> +  static_assert(ranges::distance(views::lazy_split(" t e x t "sv, ' ')) == 6);
> +  static_assert(ranges::distance(views::lazy_split("  text  "sv, "  "sv)) == 3);
> +  static_assert(ranges::distance(views::lazy_split("  text    "sv, "  "sv)) == 4);
> +  static_assert(ranges::distance(views::lazy_split("  text     "sv, "  "sv)) == 4);
> +  static_assert(ranges::distance(views::lazy_split("t"sv, 't')) == 2);
> +  static_assert(ranges::distance(views::lazy_split("text"sv, ""sv)) == 4);
> +}
> +
>  int
>  main()
>  {
> @@ -206,4 +220,5 @@ main()
>    test08();
>    test09();
>    test10();
> +  test11();
>  }
> --
> 2.32.0.93.g670b81a890
>