https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:4cd69a5a0dd31bc6fdef1bbabc8d6d1416014ea1 commit r10-9831-g4cd69a5a0dd31bc6fdef1bbabc8d6d1416014ea1 Author: Jonathan Wakely <jwak...@redhat.com> Date: Mon May 17 11:54:06 2021 +0100 libstdc++: Fix filesystem::path constraints for volatile [PR 100630] The constraint check for filesystem::path construction uses decltype(__is_path_src(declval<Source>())) which mean it considers conversion from an rvalue. When Source is a volatile-qualified type it cannot use is_path_src(const Unknown&) because a const lvalue reference can only bind to a non-volatile rvalue. Since the relevant path members all have a const Source& parameter, the constraint should be defined in terms of declval<const Source&>(), not declval<Source>(). This avoids the problem of volatile-qualified rvalues, because we no longer use an rvalue at all. libstdc++-v3/ChangeLog: PR libstdc++/100630 * include/bits/fs_path.h (__is_constructible_from): Test construction from a const lvalue, not an rvalue. * include/experimental/bits/fs_path.h (__is_constructible_from): Likewise. * testsuite/27_io/filesystem/path/construct/100630.cc: New test. * testsuite/experimental/filesystem/path/construct/100630.cc: New test.
