On Wed, 8 Mar 2023 at 15:13, Patrick Palka via Libstdc++
<libstd...@gcc.gnu.org> wrote:
>
> The LWG 3820 testcase revealed a bug in _M_advance, which this patch
> also fixes.
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
OK
>
> libstdc++-v3/ChangeLog:
>
> * include/std/ranges
> (cartesian_product_view::_Iterator::_Iterator): Remove
> constraint on default constructor as per LWG 3849.
> (cartesian_product_view::_Iterator::_M_prev): Adjust position
> of _Nm > 0 test as per LWG 3820.
> (cartesian_product_view::_Iterator::_M_advance): Perform bound
> checking only on sized cartesian products.
> * testsuite/std/ranges/cartesian_product/1.cc (test08): New test.
> ---
> libstdc++-v3/include/std/ranges | 23 +++++++++++--------
> .../std/ranges/cartesian_product/1.cc | 9 ++++++++
> 2 files changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index 67566c6ebcf..14f38727198 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -8225,7 +8225,7 @@ namespace views::__adaptor
> range_reference_t<__maybe_const_t<_Const,
> _Vs>>...>;
> using difference_type =
> decltype(cartesian_product_view::_S_difference_type());
>
> - _Iterator() requires forward_range<__maybe_const_t<_Const, _First>> =
> default;
> + _Iterator() = default;
>
> constexpr
> _Iterator(_Iterator<!_Const> __i)
> @@ -8390,12 +8390,12 @@ namespace views::__adaptor
> _M_prev()
> {
> auto& __it = std::get<_Nm>(_M_current);
> - if (__it == ranges::begin(std::get<_Nm>(_M_parent->_M_bases)))
> - {
> - __it =
> __detail::__cartesian_common_arg_end(std::get<_Nm>(_M_parent->_M_bases));
> - if constexpr (_Nm > 0)
> + if constexpr (_Nm > 0)
> + if (__it == ranges::begin(std::get<_Nm>(_M_parent->_M_bases)))
> + {
> + __it =
> __detail::__cartesian_common_arg_end(std::get<_Nm>(_M_parent->_M_bases));
> _M_prev<_Nm - 1>();
> - }
> + }
> --__it;
> }
>
> @@ -8416,10 +8416,13 @@ namespace views::__adaptor
> if constexpr (_Nm == 0)
> {
> #ifdef _GLIBCXX_ASSERTIONS
> - auto __size = ranges::ssize(__r);
> - auto __begin = ranges::begin(__r);
> - auto __offset = __it - __begin;
> - __glibcxx_assert(__offset + __x >= 0 && __offset + __x <=
> __size);
> + if constexpr (sized_range<__maybe_const_t<_Const, _First>>)
> + {
> + auto __size = ranges::ssize(__r);
> + auto __begin = ranges::begin(__r);
> + auto __offset = __it - __begin;
> + __glibcxx_assert(__offset + __x >= 0 && __offset + __x <=
> __size);
> + }
> #endif
> __it += __x;
> }
> diff --git a/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc
> b/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc
> index f52c2b96d58..56ff3d152c6 100644
> --- a/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc
> @@ -201,6 +201,14 @@ test07()
> VERIFY( i == 5 );
> }
>
> +void
> +test08()
> +{
> + // LWG 3820
> + auto r = std::views::cartesian_product(std::views::iota(0));
> + r.begin() += 3; // hard error
> +}
> +
> int
> main()
> {
> @@ -211,4 +219,5 @@ main()
> test05();
> static_assert(test06());
> test07();
> + test08();
> }
> --
> 2.40.0.rc0.57.g454dfcbddf
>
