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[libc++] Fix __segmented_iterator_traits for implicit template instantiation in SFINAE #134304

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[libc++] Fix __segmented_iterator_traits for implicit template instantiation in SFINAE #134304

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20 changes: 7 additions & 13 deletions libcxx/include/__iterator/segmented_iterator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -51,28 +51,22 @@
_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Iterator>
struct __segmented_iterator_traits;
/* exposition-only:
{
using __segment_iterator = ...;
using __local_iterator = ...;
struct __segmented_iterator_traits {
using __is_segmented_iterator _LIBCPP_NODEBUG = false_type;
using __segment_iterator _LIBCPP_NODEBUG = void;
using __local_iterator _LIBCPP_NODEBUG = void;

/* exposition-only:
static __segment_iterator __segment(_Iterator);
static __local_iterator __local(_Iterator);
static __local_iterator __begin(__segment_iterator);
static __local_iterator __end(__segment_iterator);
static _Iterator __compose(__segment_iterator, __local_iterator);
*/
};
*/

template <class _Tp, size_t = 0>
struct __has_specialization : false_type {};

template <class _Tp>
struct __has_specialization<_Tp, sizeof(_Tp) * 0> : true_type {};

template <class _Iterator>
using __is_segmented_iterator _LIBCPP_NODEBUG = __has_specialization<__segmented_iterator_traits<_Iterator> >;
struct __is_segmented_iterator : __segmented_iterator_traits<_Iterator>::__is_segmented_iterator {};

_LIBCPP_END_NAMESPACE_STD

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2 changes: 2 additions & 0 deletions libcxx/include/__ranges/join_view.h
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@
#include <__ranges/range_adaptor.h>
#include <__ranges/view_interface.h>
#include <__type_traits/common_type.h>
#include <__type_traits/integral_constant.h>
#include <__type_traits/maybe_const.h>
#include <__utility/as_lvalue.h>
#include <__utility/empty.h>
Expand Down Expand Up @@ -378,6 +379,7 @@ template <class _JoinViewIterator>
__has_random_access_iterator_category<typename _JoinViewIterator::_Outer>::value &&
__has_random_access_iterator_category<typename _JoinViewIterator::_Inner>::value)
struct __segmented_iterator_traits<_JoinViewIterator> {
using __is_segmented_iterator _LIBCPP_NODEBUG = true_type;
using __segment_iterator _LIBCPP_NODEBUG =
__iterator_with_data<typename _JoinViewIterator::_Outer, typename _JoinViewIterator::_Parent*>;
using __local_iterator _LIBCPP_NODEBUG = typename _JoinViewIterator::_Inner;
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52 changes: 52 additions & 0 deletions libcxx/test/libcxx/iterators/segmented_iterator.pass.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,52 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//

// <iterator>

// __segmented_iterator_traits<_Iter>

// verifies that __segmented_iterator_traits<_Iter> does not result in implicit
// template instantaition, which may cause hard errors in SFINAE.

// XFAIL: FROZEN-CXX03-HEADERS-FIXME

#include <array>
#include <deque>
#include <list>
#include <ranges>
#include <vector>
#include <__iterator/segmented_iterator.h>
#include <__type_traits/integral_constant.h>

#include "test_iterators.h"
#include "test_macros.h"

template <class Iter>
struct is_segmented_random_access_iterator
: std::_BoolConstant<std::__is_segmented_iterator<Iter>::value &&
std::__has_random_access_iterator_category<
typename std::__segmented_iterator_traits<Iter>::__local_iterator>::value> {};

int main(int, char**) {
static_assert(is_segmented_random_access_iterator<std::deque<int>::iterator>::value, "");
static_assert(!is_segmented_random_access_iterator<std::vector<int>::iterator>::value, "");
static_assert(!is_segmented_random_access_iterator<std::list<int>::iterator>::value, "");
static_assert(!is_segmented_random_access_iterator<std::array<int, 0>::iterator>::value, "");
static_assert(!is_segmented_random_access_iterator<cpp17_input_iterator<int*> >::value, "");
static_assert(!is_segmented_random_access_iterator<forward_iterator<int*> >::value, "");
static_assert(!is_segmented_random_access_iterator<random_access_iterator<int*> >::value, "");
static_assert(!is_segmented_random_access_iterator<int*>::value, "");

#if TEST_STD_VER >= 20
using join_view_iterator = decltype((std::declval<std::vector<std::vector<int > >&>() | std::views::join).begin());
static_assert(is_segmented_random_access_iterator<join_view_iterator>::value, "");
#endif

return 0;
}