https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100824
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:a842cb9c255f66f38ddd36b10c60920ed5f189de commit r11-8555-ga842cb9c255f66f38ddd36b10c60920ed5f189de Author: Jonathan Wakely <jwak...@redhat.com> Date: Fri Jun 4 15:59:38 2021 +0100 libstdc++: Fix value categories used by ranges access CPOs [PR 100824] The implementation of P2091R0 was incomplete, so that some range access CPOs used perfect forwarding where they should not. This fixes it by consistently operating on lvalues. Some additional changes that are not necessary to fix the bug: Modify the __as_const helper to simplify its usage. Instead of deducing the value category from its argument, and requiring callers to forward the argument as the correct category, add a non-deduced template parameter which is used for the value category and accept the argument as an lvalue. This means callers say __as_const<T>(t) instead of __as_const(std::forward<T>(t)). Always use an lvalue reference type as the template argument for the _S_noexcept helpers, so that we only instantiate one specialization for lvalues and rvalues of the same type. Move some helper concepts and functions from namespace std::__detail to ranges::__cust_access, to be consistent with the ranges::begin CPO. This ensures that the __adl_begin concept and the _Begin::operator() function are in the same namespace, so unqualified lookup is consistent and the poison pills for begin are visible to both. Simplified static assertions for arrays, because the expression a+0 is already ill-formed for an array of incomplete type. Signed-off-by: Jonathan Wakely <jwak...@redhat.com> libstdc++-v3/ChangeLog: PR libstdc++/100824 * include/bits/iterator_concepts.h (__detail::__decay_copy) (__detail::__member_begin, __detail::__adl_begin): Move to namespace ranges::__cust_access. (__detail::__ranges_begin): Likewise, and rename to __begin. Remove redundant static assertion. * include/bits/ranges_base.h (_Begin, _End, _RBegin, _REnd): Use lvalue in noexcept specifier. (__as_const): Add non-deduced parameter for value category. (_CBegin, _CEnd, _CRBegin, _CREnd, _CData): Adjust uses of __as_const. (__member_size, __adl_size, __member_empty, __size0_empty): (__eq_iter_empty, __adl_data): Use lvalue objects in requirements. (__sentinel_size): Likewise. Add check for conversion to unsigned-like. (__member_data): Allow non-lvalue types to satisfy the concept, but use lvalue object in requirements. (_Size, _SSize): Remove forwarding to always use an lvalue. (_Data): Likewise. Add static assertion for arrays. * testsuite/std/ranges/access/cdata.cc: Adjust expected behaviour for rvalues. Add negative tests for ill-formed expressions. * testsuite/std/ranges/access/data.cc: Likewise. * testsuite/std/ranges/access/empty.cc: Adjust expected behaviour for rvalues. * testsuite/std/ranges/access/size.cc: Likewise. (cherry picked from commit ee9548b36a7f17e8a63585b58f340c93dcba95d8)
