diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h index d3823057270..20c0319f3a7 100644 --- a/libstdc++-v3/include/bits/stl_iterator.h +++ b/libstdc++-v3/include/bits/stl_iterator.h @@ -1822,6 +1822,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return _ReturnType(__i); } #if __cplusplus > 201703L && __glibcxx_concepts + // _GLIBCXX_RESOLVE_LIB_DEFECTS + // 3736. move_iterator missing disable_sized_sentinel_for specialization + template + requires (!sized_sentinel_for<_Iterator1, _Iterator2>) + inline constexpr bool + disable_sized_sentinel_for, + move_iterator<_Iterator2>> = true; + // [iterators.common] Common iterators namespace __detail diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3736.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3736.cc new file mode 100644 index 00000000000..eaf791b3089 --- /dev/null +++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3736.cc @@ -0,0 +1,52 @@ +// { dg-do compile { target c++20 } } + +// 3736. move_iterator missing disable_sized_sentinel_for specialization + +#include + +template using MoveIter = std::move_iterator; + +using std::sized_sentinel_for; +using std::disable_sized_sentinel_for; + +// These assertions always passed, even without LWG 3736: +static_assert(sized_sentinel_for, MoveIter>); +static_assert(sized_sentinel_for, MoveIter>); +static_assert(not sized_sentinel_for, MoveIter>); +static_assert(not sized_sentinel_for, std::default_sentinel_t>); +static_assert(not disable_sized_sentinel_for, MoveIter>); + +// These types don't satisfy sized_sentinel_for anyway (because the subtraction +// is ill-formed) but LWG 3736 makes the variable template explicitly false: +static_assert(disable_sized_sentinel_for, MoveIter>); + +struct Iter +{ + using iterator_category = std::random_access_iterator_tag; + using value_type = int; + using pointer = int*; + using reference = int&; + using difference_type = long; + + Iter() = default; + Iter& operator++(); + Iter operator++(int); + Iter& operator--(); + Iter operator--(int); + reference operator*() const; + pointer operator->() const; + Iter& operator+=(difference_type); + Iter& operator-=(difference_type); + friend Iter operator+(Iter, difference_type); + friend Iter operator+(difference_type, Iter); + friend Iter operator-(Iter, difference_type); + friend difference_type operator-(Iter, Iter); + bool operator==(Iter) const; +}; + +// Specialize the variable template so that Iter is not its own sized sentinel: +template<> constexpr bool std::disable_sized_sentinel_for = true; +static_assert( not sized_sentinel_for ); + +// LWG 3736 means that affects std::move_iterator as well: +static_assert( not sized_sentinel_for, MoveIter> );