[PATCH] Fix filesystem::equivalent for mingw

[Jonathan Wakely]

        * src/c++17/fs_ops.cc
        (equivalent(const path&, const path&, error_code&))
        [_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Use GetFileInformationByHandle to
        compare files instead of relying on incomplete info returned by stat.

Tested x86_64-linux and x86_64-w64-mingw32, committed to trunk.


commit 6c860ebca6e0b486e9b95231e175fb4084ca3f0a
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu Jan 17 14:18:38 2019 +0000

    Fix filesystem::equivalent for mingw
    
            * src/c++17/fs_ops.cc
            (equivalent(const path&, const path&, error_code&))
            [_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Use GetFileInformationByHandle to
            compare files instead of relying on incomplete info returned by 
stat.

diff --git a/libstdc++-v3/src/c++17/fs_ops.cc b/libstdc++-v3/src/c++17/fs_ops.cc
index c4b99fb36ce..3ff0ded1c66 100644
--- a/libstdc++-v3/src/c++17/fs_ops.cc
+++ b/libstdc++-v3/src/c++17/fs_ops.cc
@@ -851,7 +851,49 @@ fs::equivalent(const path& p1, const path& p2, error_code& 
ec) noexcept
       ec.clear();
       if (is_other(s1) || is_other(s2))
        return false;
+#if _GLIBCXX_FILESYSTEM_IS_WINDOWS
+      // st_ino is not set, so can't be used to distinguish files
+      if (st1.st_mode != st2.st_mode || st1.st_dev != st2.st_dev)
+       return false;
+
+      struct auto_handle {
+       explicit auto_handle(const path& p_)
+       : handle(CreateFileW(p_.c_str(), 0,
+             FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
+             0, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0))
+       { }
+
+       ~auto_handle()
+       { if (*this) CloseHandle(handle); }
+
+       explicit operator bool() const
+       { return handle != INVALID_HANDLE_VALUE; }
+
+       bool get_info()
+       { return GetFileInformationByHandle(handle, &info); }
+
+       HANDLE handle;
+       BY_HANDLE_FILE_INFORMATION info;
+      };
+      auto_handle h1(p1);
+      auto_handle h2(p2);
+      if (!h1 || !h2)
+       {
+         if (!h1 && !h2)
+           ec.assign((int)GetLastError(), generic_category());
+         return false;
+       }
+      if (!h1.get_info() || !h2.get_info())
+       {
+         ec.assign((int)GetLastError(), generic_category());
+         return false;
+       }
+      return h1.info.dwVolumeSerialNumber == h2.info.dwVolumeSerialNumber
+       && h1.info.nFileIndexHigh == h2.info.nFileIndexHigh
+       && h1.info.nFileIndexLow == h2.info.nFileIndexLow;
+#else
       return st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino;
+#endif
     }
   else if (!exists(s1) && !exists(s2))
     ec = std::make_error_code(std::errc::no_such_file_or_directory);