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libstdc++: Fix view adaptors for mixed-const sentinels and iterators (PR 95322)

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The bug report is that transform_view's sentinel<false> cannot be
compared to its iterator<true>.  The comparison is supposed to use
operator==(iterator<Const>, sentinel<Const>) after converting
sentinel<false> to sentinel<true>. However, the operator== is a hidden
friend so is not a candidate when comparing iterator<true> with
sentinel<false>. The required conversion would only happen if we'd found
the operator, but we can't find the operator until after the conversion
happens.

A new LWG issue has been reported, but not yet assigned a number.  The
solution suggested by Casey Carter is to make the hidden friends of the
sentinel types work with iterators of any const-ness, so that no
conversions are required.

Patrick Palka observed that join_view has a similar problem and a
similar fix is used for its sentinel.

	PR libstdc++/95322
	* include/std/ranges (transform_view::_Sentinel): Allow hidden
	friends to work with _Iterator<true> and _Iterator<false>.
	(join_view::_Sentinel): Likewise.
	* testsuite/std/ranges/adaptors/95322.cc: New test.
This commit is contained in:
Jonathan Wakely 2020-05-27 22:08:15 +01:00
parent 979e89a9a9
commit 6c2582c040
2 changed files with 66 additions and 45 deletions
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63
libstdc++-v3/include/std/ranges
View File

@ -1853,7 +1853,7 @@ namespace views
{ return ranges::iter_swap(__x._M_current, __y._M_current); }
friend _Iterator<!_Const>;
friend _Sentinel<_Const>;
template<bool> friend struct _Sentinel;
};
template<bool _Const>
@ -1863,13 +1863,15 @@ namespace views
using _Parent = __detail::__maybe_const_t<_Const, transform_view>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
constexpr range_difference_t<_Base>
__distance_from(const _Iterator<_Const>& __i) const
{ return _M_end - __i._M_current; }
template<bool _Const2>
constexpr range_difference_t<_Base>
__distance_from(const _Iterator<_Const2>& __i) const
{ return _M_end - __i._M_current; }
constexpr bool
__equal(const _Iterator<_Const>& __i) const
{ return __i._M_current == _M_end; }
template<bool _Const2>
constexpr bool
__equal(const _Iterator<_Const2>& __i) const
{ return __i._M_current == _M_end; }
sentinel_t<_Base> _M_end = sentinel_t<_Base>();
@ -1892,19 +1894,26 @@ namespace views
base() const
{ return _M_end; }
friend constexpr bool
operator==(const _Iterator<_Const>& __x, const _Sentinel& __y)
{ return __y.__equal(__x); }
template<bool _Const2>
requires sentinel_for<sentinel_t<_Base>,
iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
friend constexpr bool
operator==(const _Iterator<_Const2>& __x, const _Sentinel& __y)
{ return __y.__equal(__x); }
friend constexpr range_difference_t<_Base>
operator-(const _Iterator<_Const>& __x, const _Sentinel& __y)
requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base>>
{ return -__y.__distance_from(__x); }
template<bool _Const2>
requires sized_sentinel_for<sentinel_t<_Base>,
iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
friend constexpr range_difference_t<_Base>
operator-(const _Iterator<_Const2>& __x, const _Sentinel& __y)
{ return -__y.__distance_from(__x); }
friend constexpr range_difference_t<_Base>
operator-(const _Sentinel& __y, const _Iterator<_Const>& __x)
requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base>>
{ return __y.__distance_from(__x); }
template<bool _Const2>
requires sized_sentinel_for<sentinel_t<_Base>,
iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
friend constexpr range_difference_t<_Base>
operator-(const _Sentinel& __y, const _Iterator<_Const2>& __x)
{ return __y.__distance_from(__x); }
friend _Sentinel<!_Const>;
};
@ -2571,7 +2580,7 @@ namespace views
{ return ranges::iter_swap(__x._M_inner, __y._M_inner); }
friend _Iterator<!_Const>;
friend _Sentinel<_Const>;
template<bool> friend struct _Sentinel;
};
template<bool _Const>
@ -2581,9 +2590,10 @@ namespace views
using _Parent = __detail::__maybe_const_t<_Const, join_view>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
constexpr bool
__equal(const _Iterator<_Const>& __i) const
{ return __i._M_outer == _M_end; }
template<bool _Const2>
constexpr bool
__equal(const _Iterator<_Const2>& __i) const
{ return __i._M_outer == _M_end; }
sentinel_t<_Base> _M_end = sentinel_t<_Base>();
@ -2601,9 +2611,12 @@ namespace views
: _M_end(std::move(__s._M_end))
{ }
friend constexpr bool
operator==(const _Iterator<_Const>& __x, const _Sentinel& __y)
{ return __y.__equal(__x); }
template<bool _Const2>
requires sentinel_for<sentinel_t<_Base>,
iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
friend constexpr bool
operator==(const _Iterator<_Const2>& __x, const _Sentinel& __y)
{ return __y.__equal(__x); }
friend _Sentinel<!_Const>;
};

48
libstdc++-v3/testsuite/std/ranges/adaptors/95322.cc
View File

@ -15,36 +15,44 @@
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// { dg-options "-std=gnu++2a" }
// { dg-options "-std=gnu++20" }
// { dg-do run { target c++2a } }
#include <ranges>
#include <list>
#include <testsuite_hooks.h>
#include <testsuite_iterators.h>
namespace ranges = std::ranges;
namespace views = std::views;
using __gnu_test::test_forward_range;
void
test01()
{
std::list container{1, 2, 3, 4, 5};
auto v = (container
| views::take(3)
| views::transform(std::negate{})
| views::common);
auto i = ranges::cbegin(v);
VERIFY( *i == -1 );
++i;
VERIFY( *i == -2 );
++i;
VERIFY( *i == -3 );
++i;
VERIFY( i == ranges::end(v) );
// PR libstdc++/95322
int a[2]{1, 2};
test_forward_range<int> v{a};
auto view1 = v | std::views::take(2);
auto view2 = view1 | std::views::transform(std::identity{});
const bool eq = std::ranges::cbegin(view2) == std::ranges::end(view2);
VERIFY( !eq );
}
int
main()
void
test02()
{
using irange = test_forward_range<int>;
int a[2]{1, 2};
int b[3]{3, 4, 5};
irange u[2]{ irange{a}, irange{b} };
test_forward_range<irange> v{u};
auto view = (std::views::counted(v.begin(), 2)
| std::views::transform(std::identity{})
| std::views::join);
const bool eq = std::ranges::cbegin(view) == std::ranges::end(view);
VERIFY( !eq );
}
int main()
{
test01();
test02();
}