From 4342c50ca84ae5448c0128c52120f4fe9005f203 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Fri, 28 Feb 2025 09:39:57 -0500 Subject: [PATCH] libstdc++: Fix constraint recursion in basic_const_iterator relops [PR112490] Here for using RCI = reverse_iterator::iterator>> static_assert(std::totally_ordered); we effectively need to check the requirement requires (RCI x) { x RELOP x; } for each RELOP in {<, >, <=, >=} which we expect to be straightforwardly satisfied by reverse_iterator's namespace-scope relops. But due to ADL we find ourselves also considering the basic_const_iterator relop friends, which before CWG 2369 would be quickly discarded since RCI clearly isn't convertible to basic_const_iterator. After CWG 2369 though we must first check these relops' constraints (with _It = vector::iterator and _It2 = RCI), which entails checking totally_ordered recursively. This patch fixes this by turning the problematic non-dependent function parameters of type basic_const_iterator<_It> into dependent ones of type basic_const_iterator<_It3> where _It3 is constrained to match _It. Thus the basic_const_iterator relop friends now get quickly discarded during deduction and before the constraint check if the second operand isn't a specialization of basic_const_iterator (or derived from one) like before CWG 2369. PR libstdc++/112490 libstdc++-v3/ChangeLog: * include/bits/stl_iterator.h (basic_const_iterator::operator<): Replace non-dependent basic_const_iterator function parameter with a dependent one of type basic_const_iterator<_It3> where _It3 matches _It. (basic_const_iterator::operator>): Likewise. (basic_const_iterator::operator<=): Likewise. (basic_const_iterator::operator>=): Likewise. * testsuite/24_iterators/const_iterator/112490.cc: New test. Reviewed-by: Jonathan Wakely --- libstdc++-v3/include/bits/stl_iterator.h | 16 ++++++++-------- .../24_iterators/const_iterator/112490.cc | 12 ++++++++++++ 2 files changed, 20 insertions(+), 8 deletions(-) create mode 100644 libstdc++-v3/testsuite/24_iterators/const_iterator/112490.cc diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h index 3e025342fb5..33732b1a428 100644 --- a/libstdc++-v3/include/bits/stl_iterator.h +++ b/libstdc++-v3/include/bits/stl_iterator.h @@ -2881,30 +2881,30 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION && three_way_comparable_with<_It, _It2> { return _M_current <=> __y; } - template<__detail::__not_a_const_iterator _It2> + template<__detail::__not_a_const_iterator _It2, same_as<_It> _It3> friend constexpr bool - operator<(const _It2& __x, const basic_const_iterator& __y) + operator<(const _It2& __x, const basic_const_iterator<_It3>& __y) noexcept(noexcept(__x < __y._M_current)) requires random_access_iterator<_It> && totally_ordered_with<_It, _It2> { return __x < __y._M_current; } - template<__detail::__not_a_const_iterator _It2> + template<__detail::__not_a_const_iterator _It2, same_as<_It> _It3> friend constexpr bool - operator>(const _It2& __x, const basic_const_iterator& __y) + operator>(const _It2& __x, const basic_const_iterator<_It3>& __y) noexcept(noexcept(__x > __y._M_current)) requires random_access_iterator<_It> && totally_ordered_with<_It, _It2> { return __x > __y._M_current; } - template<__detail::__not_a_const_iterator _It2> + template<__detail::__not_a_const_iterator _It2, same_as<_It> _It3> friend constexpr bool - operator<=(const _It2& __x, const basic_const_iterator& __y) + operator<=(const _It2& __x, const basic_const_iterator<_It3>& __y) noexcept(noexcept(__x <= __y._M_current)) requires random_access_iterator<_It> && totally_ordered_with<_It, _It2> { return __x <= __y._M_current; } - template<__detail::__not_a_const_iterator _It2> + template<__detail::__not_a_const_iterator _It2, same_as<_It> _It3> friend constexpr bool - operator>=(const _It2& __x, const basic_const_iterator& __y) + operator>=(const _It2& __x, const basic_const_iterator<_It3>& __y) noexcept(noexcept(__x >= __y._M_current)) requires random_access_iterator<_It> && totally_ordered_with<_It, _It2> { return __x >= __y._M_current; } diff --git a/libstdc++-v3/testsuite/24_iterators/const_iterator/112490.cc b/libstdc++-v3/testsuite/24_iterators/const_iterator/112490.cc new file mode 100644 index 00000000000..9bb154847cf --- /dev/null +++ b/libstdc++-v3/testsuite/24_iterators/const_iterator/112490.cc @@ -0,0 +1,12 @@ +// { dg-do compile { target c++23 } } + +// PR libstdc++/112490 - infinite meta error in +// reverse_iterator::iterator>> + +#include +#include + +using I = std::vector::iterator; +using CI = std::basic_const_iterator; +using RCI = std::reverse_iterator; +static_assert(std::totally_ordered);