[committed] libstdc++: Implement LWG 2937 for std::filesystem::equivalent [PR118158]

[Jonathan Wakely]

On Thu, 16 Jan 2025 at 09:50, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> Do not report an error for (is_other(s1) && is_other(s2)) as the
> standard originally said, nor for (is_other(s1) || is_other(s2)) as
> libstdc++ was doing. We can compare inode numbers for special files and
> so give sensible answers.
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/118158
>         * src/c++17/fs_ops.cc (fs::equivalent): Remove error reporting
>         for is_other(s1) && is_other(s2) case, as per LWG 2937.
>         * testsuite/27_io/filesystem/operations/pr118158.cc: New test.
> ---
>
> Tested x86_64-linux. Pushed to trunk.
>
> I'm expecting the new test's use of mkfifo to fail on some targets, e.g.
> maybe rtems. We can either tweak the #if or add target selectors to
> exclude those targets when we discover which ones FAIL.

Ah, it FAILs on mingw-w64 for a start.

>
>  libstdc++-v3/src/c++17/fs_ops.cc              | 22 +++----
>  .../27_io/filesystem/operations/pr118158.cc   | 62 +++++++++++++++++++
>  2 files changed, 69 insertions(+), 15 deletions(-)
>  create mode 100644 libstdc++-v3/testsuite/27_io/filesystem/operations/pr118158.cc
>
> diff --git a/libstdc++-v3/src/c++17/fs_ops.cc b/libstdc++-v3/src/c++17/fs_ops.cc
> index 1d75f24f78e8..4f188153ae3a 100644
> --- a/libstdc++-v3/src/c++17/fs_ops.cc
> +++ b/libstdc++-v3/src/c++17/fs_ops.cc
> @@ -914,24 +914,16 @@ fs::equivalent(const path& p1, const path& p2, error_code& ec) noexcept
>    else
>      err = errno;
>
> -  if (exists(s1) && exists(s2))
> -    {
> -      if (is_other(s1) && is_other(s2))
> -       {
> -         ec = std::__unsupported();
> -         return false;
> -       }
> -      ec.clear();
> -      if (is_other(s1) || is_other(s2))
> -       return false;
> -      return fs::equiv_files(p1.c_str(), st1, p2.c_str(), st2, ec);
> -    }
> +  if (err)
> +    ec.assign(err, std::generic_category());
>    else if (!exists(s1) || !exists(s2))
>      ec = std::make_error_code(std::errc::no_such_file_or_directory);
> -  else if (err)
> -    ec.assign(err, std::generic_category());
>    else
> -    ec.clear();
> +    {
> +      ec.clear();
> +      if (s1.type() == s2.type())
> +       return fs::equiv_files(p1.c_str(), st1, p2.c_str(), st2, ec);
> +    }
>    return false;
>  #else
>    ec = std::make_error_code(std::errc::function_not_supported);
> diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/pr118158.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/pr118158.cc
> new file mode 100644
> index 000000000000..b57a2d184f41
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/pr118158.cc
> @@ -0,0 +1,62 @@
> +// { dg-do run { target c++17 } }
> +// { dg-require-filesystem-ts "" }
> +
> +#include <filesystem>
> +#include <testsuite_fs.h>
> +#include <testsuite_hooks.h>
> +
> +#if defined(_GLIBCXX_HAVE_SYS_STAT_H) && defined(_GLIBCXX_HAVE_SYS_TYPES_H)
> +# include <sys/types.h>
> +# include <sys/stat.h>  // mkfifo
> +#endif
> +
> +namespace fs = std::filesystem;
> +
> +void
> +test_pr118158()
> +{
> +#if defined(_GLIBCXX_HAVE_SYS_STAT_H) && defined(_GLIBCXX_HAVE_SYS_TYPES_H) \
> +  && defined(S_IWUSR) && defined(S_IRUSR)
> +  auto p1 = __gnu_test::nonexistent_path();
> +  auto p2 = __gnu_test::nonexistent_path();
> +  auto p3 = __gnu_test::nonexistent_path();
> +  const std::error_code bad_ec = make_error_code(std::errc::invalid_argument);
> +  std::error_code ec;
> +  bool result;
> +
> +  VERIFY( ! ::mkfifo(p1.c_str(), S_IWUSR | S_IRUSR) );
> +  __gnu_test::scoped_file f1(p1, __gnu_test::scoped_file::adopt_file);
> +
> +  // Special file is equivalent to itself.
> +  VERIFY( equivalent(p1, p1) );
> +  VERIFY( equivalent(p1, p1, ec) );
> +  VERIFY( ! ec );
> +
> +  VERIFY( ! ::mkfifo(p2.c_str(), S_IWUSR | S_IRUSR) );
> +  __gnu_test::scoped_file f2(p2, __gnu_test::scoped_file::adopt_file);
> +
> +  ec = bad_ec;
> +  // Distinct special files are not equivalent.
> +  VERIFY( ! equivalent(p1, p2, ec) );
> +  VERIFY( ! ec );
> +
> +  // Non-existent paths are always an error.
> +  VERIFY( ! equivalent(p1, p3, ec) );
> +  VERIFY( ec == std::errc::no_such_file_or_directory );
> +  ec = bad_ec;
> +  VERIFY( ! equivalent(p3, p2, ec) );
> +  VERIFY( ec == std::errc::no_such_file_or_directory );
> +
> +  // Special file is not equivalent to regular file.
> +  __gnu_test::scoped_file f3(p3);
> +  ec = bad_ec;
> +  VERIFY( ! equivalent(p1, p3, ec) );
> +  VERIFY( ! ec );
> +#endif
> +}
> +
> +int
> +main()
> +{
> +  test_pr118158();
> +}
> --
> 2.47.1
>