[PATCH] Fix overwriting files with fs::copy_file on windows

["Björn Schäpers" <gcc@hazardy.de>]

From: Björn Schäpers <bjoern@hazardy.de>

This fixes i.e. https://github.com/msys2/MSYS2-packages/issues/1937
I don't know if I picked the right way to do it.

When acceptable I think the declaration should be moved into
ops-common.h, since then we could use stat_type and also use that in the
commonly used function.

Manually tested on i686-w64-mingw32.

-- >8 --
libstdc++: Fix overwriting files on windows

The inodes have no meaning on windows, thus all files have an inode of
0. Use a differenz approach to identify equivalent files. As a result
std::filesystem::copy_file did not honor
copy_options::overwrite_existing. Factored the method out of
std::filesystem::equivalent.

libstdc++-v3/Changelog:

	* include/bits/fs_ops.h: Add declaration of
	  __detail::equivalent_win32.
	* src/c++17/fs_ops.cc (__detail::equivalent_win32): Implement it
	(fs::equivalent): Use __detail::equivalent_win32, factored the
	old test out.
	* src/filesystem/ops-common.h (_GLIBCXX_FILESYSTEM_IS_WINDOWS):
	  Use the function.

Signed-off-by: Björn Schäpers <bjoern@hazardy.de>
---
 libstdc++-v3/include/bits/fs_ops.h       |  8 +++
 libstdc++-v3/src/c++17/fs_ops.cc         | 79 +++++++++++++-----------
 libstdc++-v3/src/filesystem/ops-common.h | 10 ++-
 3 files changed, 60 insertions(+), 37 deletions(-)

diff --git a/libstdc++-v3/include/bits/fs_ops.h b/libstdc++-v3/include/bits/fs_ops.h
index 90650c47b46..d10b78a4bdd 100644
--- a/libstdc++-v3/include/bits/fs_ops.h
+++ b/libstdc++-v3/include/bits/fs_ops.h
@@ -40,6 +40,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 namespace filesystem
 {
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+namespace __detail
+{
+  bool
+  equivalent_win32(const wchar_t* p1, const wchar_t* p2, error_code& ec);
+} // namespace __detail
+#endif //_GLIBCXX_FILESYSTEM_IS_WINDOWS
+
   /** @addtogroup filesystem
    *  @{
    */
diff --git a/libstdc++-v3/src/c++17/fs_ops.cc b/libstdc++-v3/src/c++17/fs_ops.cc
index 61df19753ef..3cc87d45237 100644
--- a/libstdc++-v3/src/c++17/fs_ops.cc
+++ b/libstdc++-v3/src/c++17/fs_ops.cc
@@ -67,6 +67,49 @@
 namespace fs = std::filesystem;
 namespace posix = std::filesystem::__gnu_posix;
 
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+bool
+fs::__detail::equivalent_win32(const wchar_t* p1, const wchar_t* p2,
+			       error_code& ec)
+{
+  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 = __last_system_error();
+      return false;
+    }
+  if (!h1.get_info() || !h2.get_info())
+    {
+      ec = __last_system_error();
+      return false;
+    }
+  return h1.info.dwVolumeSerialNumber == h2.info.dwVolumeSerialNumber
+    && h1.info.nFileIndexHigh == h2.info.nFileIndexHigh
+    && h1.info.nFileIndexLow == h2.info.nFileIndexLow;
+}
+#endif //_GLIBCXX_FILESYSTEM_IS_WINDOWS
+
 fs::path
 fs::absolute(const path& p)
 {
@@ -858,41 +901,7 @@ fs::equivalent(const path& p1, const path& p2, error_code& ec) noexcept
       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 = __last_system_error();
-	  return false;
-	}
-      if (!h1.get_info() || !h2.get_info())
-	{
-	  ec = __last_system_error();
-	  return false;
-	}
-      return h1.info.dwVolumeSerialNumber == h2.info.dwVolumeSerialNumber
-	&& h1.info.nFileIndexHigh == h2.info.nFileIndexHigh
-	&& h1.info.nFileIndexLow == h2.info.nFileIndexLow;
+      return __detail::equivalent_win32(p1.c_str(), p2.c_str(), ec);
 #else
       return st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino;
 #endif
diff --git a/libstdc++-v3/src/filesystem/ops-common.h b/libstdc++-v3/src/filesystem/ops-common.h
index d917fddbeb1..7e67286bd01 100644
--- a/libstdc++-v3/src/filesystem/ops-common.h
+++ b/libstdc++-v3/src/filesystem/ops-common.h
@@ -489,8 +489,14 @@ _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
 	    return false;
 	  }
 
-	if (to_st->st_dev == from_st->st_dev
-	    && to_st->st_ino == from_st->st_ino)
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+	// st_ino is not set, so can't be used to distinguish files
+	std::error_code not_used;
+	if (st1.st_mode != st2.st_mode || st1.st_dev != st2.st_dev ||
+	    fs::__detail::equivalent_win32(from, to, not_used))
+#else
+	if (st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino)
+#endif
 	  {
 	    ec = std::make_error_code(std::errc::file_exists);
 	    return false;
-- 
2.44.0