add workarounds for UNC path bugs in std::filesystem::exists() on mingw

The mingw implementation of `std::filesystem::exists()` doesn't work
for UNC paths, even if the referenced file or directory exists. However,
both `std::filesystem::is_directory()` and
`std::filesystem::is_regular_file()` do work; so let's use those
instead of `…exists()`.

The result was that mkvmerge & MKVToolNix GUI couldn't find base
directories for Blu-rays & DVDs when UNC paths were used.

Corresponding gcc bug:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99311

Part of the fix of #3037.

src/common/bluray/disc_library.cpp

@@ -132,7 +132,7 @@ locate_and_parse(std::filesystem::path const &location) {
     return {};
 
   auto disc_library_dir = base_dir / "META" / "DL";
-  if (!std::filesystem::exists(disc_library_dir) || !std::filesystem::is_directory(disc_library_dir))
+  if (!std::filesystem::is_directory(disc_library_dir))
     return {};
 
   mxdebug_if(debug, fmt::format("found DL directory at {}\n", disc_library_dir));
@@ -170,7 +170,7 @@ locate_and_parse_for_language(std::filesystem::path const &location,
     return {};
 
   auto disc_library_file = base_dir / "META" / "DL" / fmt::format("bdmt_{}.xml", language);
-  if (!std::filesystem::exists(disc_library_file))
+  if (!std::filesystem::is_regular_file(disc_library_file))
     return {};
 
   mxdebug_if(debug, fmt::format("found DL file for language {} at {}\n", language, disc_library_file));

src/common/bluray/track_chapter_names.cpp

@@ -70,7 +70,7 @@ locate_and_parse_for_title(std::filesystem::path const &location,
     return {};
 
   auto track_chapter_names_dir = base_dir / "META" / "TN";
-  if (!std::filesystem::exists(track_chapter_names_dir) || !std::filesystem::is_directory(track_chapter_names_dir))
+  if (!std::filesystem::is_directory(track_chapter_names_dir))
     return {};
 
   mxdebug_if(debug, fmt::format("found TN directory at {}\n", track_chapter_names_dir));

src/common/bluray/util.cpp

@@ -58,7 +58,7 @@ find_other_file_impl(std::filesystem::path const &reference_file_name,
     return {};
 
   auto file_name = base_dir / other_file_name;
-  if (std::filesystem::exists(file_name))
+  if (std::filesystem::is_regular_file(file_name))
     return file_name;
 
   return {};

src/common/chapters/dvd.cpp

@@ -136,10 +136,9 @@ maybe_parse_dvd(std::string const &file_name,
   if (mtx::regex::match(cleaned_file_name, mtx::regex::jp::Regex{"\\.(bup|ifo|vob)$", "i"}))
     dvd_dir = dvd_dir.parent_path();
 
-  else if (   !std::filesystem::exists(dvd_dir)
-           || !std::filesystem::is_directory(dvd_dir)
-           || (   !std::filesystem::exists(dvd_dir / "VIDEO_TS.IFO")
-               && !std::filesystem::exists(dvd_dir / "VIDEO_TS" / "VIDEO_TS.IFO")))
+  else if (   !std::filesystem::is_directory(dvd_dir)
+           || (   !std::filesystem::is_regular_file(dvd_dir / "VIDEO_TS.IFO")
+               && !std::filesystem::is_regular_file(dvd_dir / "VIDEO_TS" / "VIDEO_TS.IFO")))
     return {};
 
   auto titles_and_timestamps = parse_dvd(dvd_dir.u8string());

src/common/fs_sys_helpers/unix.cpp

@@ -66,7 +66,7 @@ get_application_data_folder() {
   // If $HOME/.mkvtoolnix exists already then keep using it to avoid
   // losing existing user configuration.
   auto old_default_folder = mtx::fs::to_path(home) / ".mkvtoolnix";
-  if (std::filesystem::exists(old_default_folder))
+  if (std::filesystem::is_directory(old_default_folder))
     return old_default_folder;
 
   // If XDG_CONFIG_HOME is set then use that folder.
@@ -114,7 +114,7 @@ get_current_exe_path([[maybe_unused]] std::string const &argv0) {
 
 #else // SYS_APPLE
   auto exe = mtx::fs::to_path("/proc/self/exe");
-  if (std::filesystem::exists(exe)) {
+  if (std::filesystem::is_regular_file(exe)) {
     auto exe_path = std::filesystem::read_symlink(exe);
 
     return mtx::fs::absolute(exe_path).parent_path();
@@ -124,7 +124,7 @@ get_current_exe_path([[maybe_unused]] std::string const &argv0) {
     return std::filesystem::current_path();
 
   exe = mtx::fs::absolute(argv0);
-  if (std::filesystem::exists(exe))
+  if (std::filesystem::is_regular_file(exe))
     return exe.parent_path();
 
   return std::filesystem::current_path();

src/common/fs_sys_helpers/windows.cpp

@@ -169,7 +169,7 @@ get_current_exe_path(std::string const &) {
 bool
 is_installed() {
   auto file_to_test = get_installation_path() / "data" / "portable-app";
-  return !std::filesystem::exists(file_to_test);
+  return !std::filesystem::is_regular_file(file_to_test);
 }
 
 uint64_t

src/common/logger.cpp

@@ -101,7 +101,7 @@ file_target_c::file_target_c(std::filesystem::path file_name)
   if (!mtx::fs::is_absolute(m_file_name))
     m_file_name = std::filesystem::temp_directory_path() / m_file_name;
 
-  if (std::filesystem::exists(m_file_name)) {
+  if (std::filesystem::is_regular_file(m_file_name)) {
     std::error_code ec;
     std::filesystem::remove(m_file_name, ec);
   }
@@ -110,7 +110,7 @@ file_target_c::file_target_c(std::filesystem::path file_name)
 void
 file_target_c::log_line(std::string const &message) {
   try {
-    mm_text_io_c out(std::make_shared<mm_file_io_c>(m_file_name.u8string(), std::filesystem::exists(m_file_name) ? MODE_WRITE : MODE_CREATE));
+    mm_text_io_c out(std::make_shared<mm_file_io_c>(m_file_name.u8string(), std::filesystem::is_regular_file(m_file_name) ? MODE_WRITE : MODE_CREATE));
     out.setFilePointer(0, libebml::seek_end);
     out.puts(format_line(message));
   } catch (mtx::mm_io::exception &ex) {

src/common/mm_file_io/unix.cpp

@@ -84,7 +84,7 @@ mm_file_io_private_c::mm_file_io_private_c(std::string const &p_file_name,
 void
 mm_file_io_c::prepare_path(const std::string &path) {
   auto directory = mtx::fs::to_path(path).parent_path();
-  if (directory.empty() || std::filesystem::exists(directory))
+  if (directory.empty() || std::filesystem::is_directory(directory))
     return;
 
   std::error_code error_code;

src/common/mm_file_io/windows.cpp

@@ -204,7 +204,7 @@ mm_file_io_c::prepare_path(std::string const &path) {
 
   auto directory = mtx::fs::to_path(normalized_path).parent_path();
 
-  if (directory.empty() || std::filesystem::exists(directory))
+  if (directory.empty() || std::filesystem::is_directory(directory))
     return;
 
   auto is_unc = normalized_path.substr(0, 2) == "\\\\"s;
@@ -230,7 +230,7 @@ mm_file_io_c::prepare_path(std::string const &path) {
   }
 
   for (auto itr = to_check.rbegin(), end = to_check.rend(); itr != end; ++itr) {
-    if (std::filesystem::exists(*itr))
+    if (std::filesystem::is_directory(*itr))
       continue;
 
     std::error_code error_code;

src/extract/extract_cli_parser.cpp

@@ -258,7 +258,7 @@ extract_cli_parser_c::set_cli_mode() {
 
     mxdebug_if(m_debug, fmt::format("set_cli_mode: new mode is single\n"));
 
-  } else if (std::filesystem::exists(mtx::fs::to_path(m_current_arg))) {
+  } else if (std::filesystem::is_regular_file(mtx::fs::to_path(m_current_arg))) {
     m_cli_type            = cli_type_e::multiple;
     m_options.m_file_name = m_current_arg;
 

src/mkvtoolnix-gui/merge/attachments.cpp

@@ -567,7 +567,7 @@ Tab::addAttachmentsFromIdentifiedBluray(mtx::bluray::disc_library::info_t const
     fileName = thumbnail.m_file_name;
   }
 
-  if (fileName.empty() || !std::filesystem::exists(fileName))
+  if (fileName.empty() || !std::filesystem::is_regular_file(fileName))
     return;
 
   auto attachment = prepareFileForAttaching(Q(fileName.u8string()), true);

src/mkvtoolnix-gui/util/file_dialog.cpp

@@ -39,7 +39,7 @@ sanitizeDirectory(QString const &directory,
   auto newPath = oldPath;
   auto ec      = std::error_code{};
 
-  while (   !(std::filesystem::exists(newPath, ec) && std::filesystem::is_directory(newPath, ec))
+  while (   !std::filesystem::is_directory(newPath, ec)
          && !newPath.parent_path().empty()
          && (newPath.parent_path() != newPath))
     newPath = newPath.parent_path();

src/mkvtoolnix-gui/util/settings.cpp

@@ -902,7 +902,7 @@ Settings::exeWithPath(QString const &exe) {
 #endif  // SYS_WINDOWS
 
   for (auto const &potentialExe : potentialExes)
-    if (std::filesystem::exists(potentialExe))
+    if (std::filesystem::is_regular_file(potentialExe))
       return QDir::toNativeSeparators(to_qs(potentialExe.u8string()));
 
   auto location = QStandardPaths::findExecutable(to_qs(program.u8string()));