Add extra mount path handling for GCC on Windows

src/dos/dos_programs.cpp

@@ -63,8 +63,10 @@ void DOS_SetupPrograms(void)
 	MSG_Add("PROGRAM_MOUNT_UMOUNT_NO_VIRTUAL","Virtual Drives can not be unMOUNTed.\n");
 	MSG_Add("PROGRAM_MOUNT_DRIVEID_ERROR", "'%c' is not a valid drive identifier.\n");
 	MSG_Add("PROGRAM_MOUNT_ROOT_PATH_WARNING",
-	        "\033[31;1mWARNING: '%s' resolves to a root directory: '%s'\n"
+	        "\033[31;1mWARNING: The path \"%s\" resolves to a root directory \"%s\"\n"
 	        "Mounting a root directory is risky. Please use a subdirectory next time.\033[0m\n");
+	MSG_Add("PROGRAM_MOUNT_NO_DRIVE_PREFIX",
+	        "The absolute path \"%s\" is missing a drive prefix, such as \"c:%s\"\n");
 	MSG_Add("PROGRAM_MOUNT_NO_OPTION","Warning: Ignoring unsupported option '%s'.\n");
 	MSG_Add("PROGRAM_MOUNT_OVERLAY_NO_BASE","A normal directory needs to be MOUNTed first before an overlay can be added on top.\n");
 	MSG_Add("PROGRAM_MOUNT_OVERLAY_INCOMPAT_BASE","The overlay is NOT compatible with the drive that is specified.\n");

src/dos/program_mount.cpp

@@ -243,7 +243,55 @@ void MOUNT::Run(void) {
 		if (!cmd->FindCommand(2, temp_line) || temp_line.empty()) {
 			goto showusage;
 		}
+
+		// Error-code to be used in throw-free std::filesystem calls
 		std::error_code ec;
+
+// Extra handling for MinGW GCC build handles the following:
+//        - mount c ./   -> should behave like mount c .
+//        - mount c /    -> should behave like mount c c:/
+//        - mount c c:   -> should behave like mount c c:/
+//
+// Note: MSVC and Clang do not need this extra babysitting.
+//       Remove this block when MinGW's GCC std::filesystem is fixed.
+//
+#if defined(WIN32) && defined(__GNUC__) && !defined(__clang__)
+		const auto saved_line = temp_line;
+
+		// GCC on Windows has problems with traling slashes, so strip them
+		const bool has_drive_spec = (temp_line.size() > 1 && temp_line[1] == ':');
+		const size_t strip_slashes_up_to = has_drive_spec ? 3 : 1;
+		while (temp_line.size() > strip_slashes_up_to &&
+		       (temp_line.back() == '/' || temp_line.back() == '\\'))
+			temp_line.pop_back();
+
+		// GCC on Windows doesn't upgrade drive-specs (d:) to absolute (d:\)
+		if (temp_line.size() == 2 && temp_line[1] == ':')
+			temp_line += '\\';
+
+		// GCC on Windows doesn't map absolute paths (/) to the current drive
+		const bool is_absolute = (temp_line.size() &&
+		                          (temp_line.front() == '/' ||
+		                           temp_line.front() == '\\'));
+
+		if (is_absolute) {
+			// Try to prepend the current-working drive
+			auto cp = std_fs::current_path(ec);
+			if (cp.has_root_name()) {
+				temp_line = cp.root_name().string() + temp_line;
+			} else {
+				WriteOut(MSG_Get("PROGRAM_MOUNT_NO_DRIVE_PREFIX"),
+				         saved_line.c_str(), saved_line.c_str());
+				return;
+			}
+		}
+
+		// if we made it here, the path is relative or has a drive
+		// prefix, which is sufficient for GCC to handle properly
+		assert(temp_line.size());
+#endif
+
+		// Construct a std::filesystem path from the string
 		std_fs::path host_path = temp_line;
 
 		// Check if the path is relative to the last config file

src/misc/support.cpp

@@ -396,6 +396,14 @@ const std_fs::path &GetExecutablePath()
 
 bool is_path_a_root_path(const std_fs::path &test_path, std_fs::path &root_path)
 {
+
+// Special handling for GCC on Windows
+#if defined(WIN32) && defined(__GNUC__) && !defined(__clang__)
+	const bool is_root_path = (test_path.string().length() == 3 && test_path.string()[1] == ':');
+	root_path = is_root_path ? test_path : std_fs::path("");
+	return is_root_path;
+#endif
+
 	// Try to discover the root path dynamically, which means we can handle
 	// all variety of filesystems like MorphOS, AmigaOS, etc.
 	std::error_code ec;
@@ -408,6 +416,8 @@ bool is_path_a_root_path(const std_fs::path &test_path, std_fs::path &root_path)
 		root_path = test_path.root_directory();
 	else if (test_path.has_root_path())
 		root_path = test_path.root_path();
+	else if (std_fs::current_path(ec).has_root_path())
+		root_path = std_fs::current_path(ec).root_path();
 
 	// Otherwise fallback to our best guess of the root path
 	if (root_path.empty())