Work around C++20 std::filesystem changes related to u8string

Source/Core/Common/FileSearch.cpp

@@ -7,6 +7,7 @@
 
 #include "Common/CommonPaths.h"
 #include "Common/FileSearch.h"
+#include "Common/StringUtil.h"
 
 #ifdef _MSC_VER
 #include <Windows.h>
@@ -74,7 +75,7 @@ std::vector<std::string> DoFileSearch(const std::vector<std::string>& directorie
 
   std::vector<fs::path> native_exts;
   for (const auto& ext : exts)
-    native_exts.push_back(fs::u8path(ext));
+    native_exts.push_back(StringToPath(ext));
 
   // N.B. This avoids doing any copies
   auto ext_matches = [&native_exts](const fs::path& path) {
@@ -93,11 +94,11 @@ std::vector<std::string> DoFileSearch(const std::vector<std::string>& directorie
   auto add_filtered = [&](const fs::directory_entry& entry) {
     auto& path = entry.path();
     if (accept_all || (ext_matches(path) && !fs::is_directory(path)))
-      result.emplace_back(path.u8string());
+      result.emplace_back(PathToString(path));
   };
   for (const auto& directory : directories)
   {
-    const fs::path directory_path = fs::u8path(directory);
+    const fs::path directory_path = StringToPath(directory);
     if (fs::is_directory(directory_path))  // Can't create iterators for non-existant directories
     {
       if (recursive)

Source/Core/Common/StringUtil.cpp

@@ -623,3 +623,26 @@ std::string UTF16BEToUTF8(const char16_t* str, size_t max_size)
 }
 
 #endif
+
+#ifdef HAS_STD_FILESYSTEM
+// This is a replacement for path::u8path, which is deprecated starting with C++20.
+std::filesystem::path StringToPath(std::string_view path)
+{
+#ifdef _MSC_VER
+  return std::filesystem::path(UTF8ToUTF16(std::string(path)));
+#else
+  return std::filesystem::path(path);
+#endif
+}
+
+// This is a replacement for path::u8string that always has the return type std::string.
+// path::u8string returns std::u8string starting with C++20, which is annoying to convert.
+std::string PathToString(const std::filesystem::path& path)
+{
+#ifdef _MSC_VER
+  return UTF16ToUTF8(path.native());
+#else
+  return path.native();
+#endif
+}
+#endif

Source/Core/Common/StringUtil.h

@@ -14,6 +14,11 @@
 
 #include "Common/CommonTypes.h"
 
+#ifdef _MSC_VER
+#include <filesystem>
+#define HAS_STD_FILESYSTEM
+#endif
+
 std::string StringFromFormatV(const char* format, va_list args);
 
 std::string StringFromFormat(const char* format, ...)
@@ -153,6 +158,11 @@ inline std::string UTF8ToTStr(const std::string& str)
 
 #endif
 
+#ifdef HAS_STD_FILESYSTEM
+std::filesystem::path StringToPath(std::string_view path);
+std::string PathToString(const std::filesystem::path& path);
+#endif
+
 // Thousand separator. Turns 12345678 into 12,345,678
 template <typename I>
 std::string ThousandSeparate(I value, int spaces = 0)

Source/Core/Core/Boot/Boot.cpp

@@ -88,7 +88,7 @@ static std::vector<std::string> ReadM3UFile(const std::string& m3u_path,
     if (!line.empty() && line.front() != '#')  // Comments start with #
     {
 #ifdef HAS_STD_FILESYSTEM
-      const std::string path_to_add = (fs::u8path(folder_path) / fs::u8path(line)).u8string();
+      const std::string path_to_add = PathToString(StringToPath(folder_path) / StringToPath(line));
 #else
       const std::string path_to_add = line.front() != '/' ? folder_path + line : line;
 #endif