On 17/05/21 15:02 +0100, Jonathan Wakely wrote:
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. Tested x86_64-linux, pushed to gcc-10 (this isn't needed for gcc-11 or trunk, but I also plan to backport it to gcc-9).
Oh actually this is needed for experimental::filesystem::path on trun kand gcc-11 (as I found when I added to the new tests to trunk) so I'll fix it there too.
