https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112490
--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:4342c50ca84ae5448c0128c52120f4fe9005f203 commit r15-7757-g4342c50ca84ae5448c0128c52120f4fe9005f203 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>
