On Wed, 16 Jul 2025, 14:46 Luc Grosheintz, <luc.groshei...@gmail.com> wrote:
> PR121061 consists of two bugs for mdspan related code. This commit fixes
> the first one. Namely, when passing custom IndexType as an array or
> span, the conversion to int must be const. Prior to this commit the
> constraint incorrectly also allowed non-const conversion. This commit
> updates all related constraints to check
>
> __valid_index_type<const OtherIndexType&, index_type>
>
> in those cases. Also adds a MutatingInt to int_like.h which only
> supports non-const conversion to int and updates the tests.
>
OK for trunk
> PR libstdc++/121061
>
> libstdc++-v3/ChangeLog:
>
> * include/std/mdspan (extents::extents): Fix constraint to
> prevent non-const conversion to index_type.
> (layout_stride::mapping::mapping): Ditto.
> (mdspan::mdspan): Ditto.
> (mdspan::operator[]): Ditto.
> * testsuite/23_containers/mdspan/extents/custom_integer.cc: Add
> test for MutatingInt.
> * testsuite/23_containers/mdspan/int_like.h (MutatingInt): Add.
> * testsuite/23_containers/mdspan/layouts/mapping.cc: Add test for
> MutatingInt.
> * testsuite/23_containers/mdspan/layouts/stride.cc: Ditto.
> * testsuite/23_containers/mdspan/mdspan.cc: Ditto.
>
> Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
> ---
> libstdc++-v3/include/std/mdspan | 34 +++++++++++--------
> .../mdspan/extents/custom_integer.cc | 1 +
> .../testsuite/23_containers/mdspan/int_like.h | 7 ++++
> .../23_containers/mdspan/layouts/mapping.cc | 3 ++
> .../23_containers/mdspan/layouts/stride.cc | 1 +
> .../testsuite/23_containers/mdspan/mdspan.cc | 2 ++
> 6 files changed, 34 insertions(+), 14 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/mdspan
> b/libstdc++-v3/include/std/mdspan
> index b34116a85e6..930997e9536 100644
> --- a/libstdc++-v3/include/std/mdspan
> +++ b/libstdc++-v3/include/std/mdspan
> @@ -288,15 +288,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> initializer_list{_S_storage::_S_int_cast(__exts)...}))
> { }
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType,
> size_t _Nm>
> - requires (_Nm == rank() || _Nm == rank_dynamic())
> + template<typename _OIndexType, size_t _Nm>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> + && (_Nm == rank() || _Nm == rank_dynamic())
> constexpr explicit(_Nm != rank_dynamic())
> extents(span<_OIndexType, _Nm> __exts) noexcept
> : _M_exts(span<const _OIndexType, _Nm>(__exts))
> { }
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType,
> size_t _Nm>
> - requires (_Nm == rank() || _Nm == rank_dynamic())
> + template<typename _OIndexType, size_t _Nm>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> + && (_Nm == rank() || _Nm == rank_dynamic())
> constexpr explicit(_Nm != rank_dynamic())
> extents(const array<_OIndexType, _Nm>& __exts) noexcept
> : _M_exts(span<const _OIndexType, _Nm>(__exts))
> @@ -878,7 +880,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> constexpr
> mapping(const mapping&) noexcept = default;
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType>
> + template<typename _OIndexType>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> constexpr
> mapping(const extents_type& __exts,
> span<_OIndexType, extents_type::rank()> __strides) noexcept
> @@ -888,7 +891,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> _M_strides[__i] = index_type(as_const(__strides[__i]));
> }
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType>
> + template<typename _OIndexType>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> constexpr
> mapping(const extents_type& __exts,
> const array<_OIndexType, extents_type::rank()>& __strides)
> @@ -1134,9 +1138,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> _M_handle(std::move(__handle))
> { }
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType,
> - size_t _Nm>
> - requires (_Nm == rank() || _Nm == rank_dynamic())
> + template<typename _OIndexType, size_t _Nm>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> + && (_Nm == rank() || _Nm == rank_dynamic())
> && is_constructible_v<mapping_type, extents_type>
> && is_default_constructible_v<accessor_type>
> constexpr explicit(_Nm != rank_dynamic())
> @@ -1145,9 +1149,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> _M_handle(std::move(__handle))
> { }
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType,
> - size_t _Nm>
> - requires (_Nm == rank() || _Nm == rank_dynamic())
> + template<typename _OIndexType, size_t _Nm>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> + && (_Nm == rank() || _Nm == rank_dynamic())
> && is_constructible_v<mapping_type, extents_type>
> && is_default_constructible_v<accessor_type>
> constexpr explicit(_Nm != rank_dynamic())
> @@ -1218,7 +1222,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> return _M_accessor.access(_M_handle, __index);
> }
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType>
> + template<typename _OIndexType>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> constexpr reference
> operator[](span<_OIndexType, rank()> __indices) const
> {
> @@ -1228,7 +1233,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> return __call(make_index_sequence<rank()>());
> }
>
> - template<__mdspan::__valid_index_type<index_type> _OIndexType>
> + template<typename _OIndexType>
> + requires __mdspan::__valid_index_type<const _OIndexType&,
> index_type>
> constexpr reference
> operator[](const array<_OIndexType, rank()>& __indices) const
> { return (*this)[span<const _OIndexType, rank()>(__indices)]; }
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
> index 4f631815b10..92c2ebb46e1 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/extents/custom_integer.cc
> @@ -84,6 +84,7 @@ main()
> test_shape_all<int, true>();
> test_shape_all<IntLike, true>();
> test_shape_all<ThrowingInt, false>();
> + test_shape_all<MutatingInt, false>();
>
> test_pack_all<int, true>();
> test_pack_all<IntLike, true>();
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
> b/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
> index ed45375f986..f4f4a773193 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/int_like.h
> @@ -5,6 +5,7 @@ enum class CustomIndexKind
> {
> Const,
> Throwing,
> + Mutating,
> };
>
> template<CustomIndexKind Kind>
> @@ -36,12 +37,18 @@ template<CustomIndexKind Kind>
> requires (Kind == CustomIndexKind::Throwing)
> { return _M_i; }
>
> + constexpr
> + operator int() noexcept
> + requires (Kind == CustomIndexKind::Mutating)
> + { return _M_i; }
> +
> private:
> int _M_i;
> };
>
> using IntLike = CustomIndexType<CustomIndexKind::Const>;
> using ThrowingInt = CustomIndexType<CustomIndexKind::Throwing>;
> +using MutatingInt = CustomIndexType<CustomIndexKind::Mutating>;
>
> struct NotIntLike
> { };
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> index 17f0c00acf2..6742fa11a51 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> @@ -180,6 +180,7 @@ template<typename Layout>
> static_assert(has_linear_index<Mapping, int>);
> static_assert(has_linear_index<Mapping, double>);
> static_assert(has_linear_index<Mapping, IntLike>);
> + static_assert(has_linear_index<Mapping, MutatingInt>);
> static_assert(!has_linear_index<Mapping, ThrowingInt>);
> static_assert(!has_linear_index<Mapping, NotIntLike>);
> static_assert(!has_linear_index<Mapping, int, int>);
> @@ -194,6 +195,7 @@ template<typename Layout>
> static_assert(has_linear_index<Mapping, int, int>);
> static_assert(has_linear_index<Mapping, double, double>);
> static_assert(has_linear_index<Mapping, IntLike, int>);
> + static_assert(has_linear_index<Mapping, MutatingInt, int>);
> static_assert(!has_linear_index<Mapping, ThrowingInt, int>);
> static_assert(!has_linear_index<Mapping, NotIntLike, int>);
> static_assert(!has_linear_index<Mapping, int, int, int>);
> @@ -524,6 +526,7 @@ template<typename Layout>
> if !consteval
> {
> test_linear_index_all<Layout, IntLike>();
> + test_linear_index_all<Layout, MutatingInt>();
> }
>
> test_required_span_size_all<Layout>();
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> index 1267306fb5c..8d2fad2936f 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> @@ -65,6 +65,7 @@ test_stride_constructible_all()
> test_stride_constructible<E0, E0, int, 0, true>();
> test_stride_constructible<E0, E0, IntLike, 0, true>();
> test_stride_constructible<E0, E0, ThrowingInt, 0, false>();
> + test_stride_constructible<E0, E0, MutatingInt, 0, false>();
> test_stride_constructible<E0, E0, NotIntLike, 0, false>();
> test_stride_constructible<E1, E1, int, 1, true>();
> test_stride_constructible<E2, E1, int, 1, true>();
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> index adabb0c6639..22ec68ea2d1 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> @@ -693,6 +693,7 @@ main()
> static_assert(test_from_int_like<int, true, true>());
> test_from_int_like<IntLike, true, true>();
> test_from_int_like<ThrowingInt, false, false>();
> + test_from_int_like<MutatingInt, true, false>();
>
> test_from_opaque_accessor();
> test_from_base_class_accessor();
> @@ -703,6 +704,7 @@ main()
> static_assert(test_access<int, true, true>());
> test_access<IntLike, true, true>();
> test_access<ThrowingInt, false, false>();
> + test_access<MutatingInt, true, false>();
>
> test_swap();
> static_assert(test_swap());
> --
> 2.50.0
>
>
