https://gcc.gnu.org/g:a3c01af5e34801aaf65ba76f4afce753e443a99c
commit r14-11414-ga3c01af5e34801aaf65ba76f4afce753e443a99c
Author: Patrick Palka <ppa...@redhat.com>
Date: Fri Feb 28 09:39:57 2025 -0500
libstdc++: Fix constraint recursion in basic_const_iterator relops
[PR112490]
Here for
using RCI = reverse_iterator<basic_const_iterator<vector<int>::iterator>>
static_assert(std::totally_ordered<RCI>);
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<int>::iterator and _It2 = RCI),
which entails checking totally_ordered<RCI> 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 <jwak...@redhat.com>
(cherry picked from commit 4342c50ca84ae5448c0128c52120f4fe9005f203)
Diff:
---
libstdc++-v3/include/bits/stl_iterator.h | 16 ++++++++--------
.../testsuite/24_iterators/const_iterator/112490.cc | 12 ++++++++++++
2 files changed, 20 insertions(+), 8 deletions(-)
diff --git a/libstdc++-v3/include/bits/stl_iterator.h
b/libstdc++-v3/include/bits/stl_iterator.h
index fff5f4015330..5e1fe30135ef 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -2865,30 +2865,30 @@ _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 000000000000..9bb154847cff
--- /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<basic_const_iterator<vector<int>::iterator>>
+
+#include <iterator>
+#include <vector>
+
+using I = std::vector<int>::iterator;
+using CI = std::basic_const_iterator<I>;
+using RCI = std::reverse_iterator<CI>;
+static_assert(std::totally_ordered<RCI>);
