Respect XDG spec for dosbox main .conf file

Windows and macOS config files are left as they were, this change
affects mostly Linux users.

Users are not forced to migrate, but visible warning is being issued if
they aren't. Majority of users probably won't notice it, as the stable
release should generate newly named .conf file.

include/cross.h

@@ -76,6 +76,8 @@
 static inline float powf (float x, float y) { return (float) pow (x,y); }
 #endif
 
+void CROSS_DetermineConfigPaths();
+
 class Cross {
 public:
 	static void GetPlatformConfigDir(std::string& in);

src/gui/sdlmain.cpp

@@ -3163,6 +3163,8 @@ int main(int argc, char* argv[]) {
 
 	sdl.num_joysticks=SDL_NumJoysticks();
 
+	CROSS_DetermineConfigPaths();
+
 	/* Parse configuration files */
 	std::string config_file, config_path, config_combined;
 	Cross::GetPlatformConfigDir(config_path);

src/misc/cross.cpp

@@ -16,26 +16,108 @@
  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */
 
-
-#include "dosbox.h"
 #include "cross.h"
-#include "support.h"
+
 #include <string>
+#include <vector>
+
 #include <limits.h>
 #include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #ifdef WIN32
 #ifndef _WIN32_IE
 #define _WIN32_IE 0x0400
 #endif
 #include <shlobj.h>
+#else
+#include <libgen.h>
 #endif
 
-#if defined HAVE_SYS_TYPES_H && defined HAVE_PWD_H
-#include <sys/types.h>
+#if defined HAVE_PWD_H
 #include <pwd.h>
 #endif
 
+#include "support.h"
+
+#ifndef WIN32
+
+std::string cached_conf_path;
+
+static bool CreateDirectories(const std::string &path)
+{
+	struct stat sb;
+	if (stat(path.c_str(), &sb) == 0) {
+		const bool is_dir = ((sb.st_mode & S_IFMT) == S_IFDIR);
+		return is_dir;
+	}
+
+	std::vector<char> tmp(path.begin(), path.end());
+	std::string dname = dirname(tmp.data());
+
+	// Create parent directories recursively
+	if (!CreateDirectories(dname))
+		return false;
+
+	return (mkdir(path.c_str(), 0700) == 0);
+}
+
+static std::string GetConfigName()
+{
+	std::string file_name;
+	Cross::GetPlatformConfigName(file_name);
+	return file_name;
+}
+
+static std::string ResolveHome(std::string tilde_path)
+{
+	Cross::ResolveHomedir(tilde_path);
+	return tilde_path;
+}
+
+static bool PathExists(const std::string &path)
+{
+	return (access(path.c_str(), F_OK) == 0);
+}
+
+static std::string DetermineConfigPath()
+{
+	const char *xdg_conf_home = getenv("XDG_CONFIG_HOME");
+	const std::string conf_home = xdg_conf_home ? xdg_conf_home : "~/.config";
+	const std::string conf_path = ResolveHome(conf_home + "/dosbox");
+	const std::string old_conf_path = ResolveHome("~/.dosbox");
+
+	if (PathExists(conf_path + "/" + GetConfigName())) {
+		return conf_path;
+	}
+
+	if (PathExists(old_conf_path + "/" + GetConfigName())) {
+		LOG_MSG("WARNING: Config file found in deprecated path! (~/.dosbox)\n"
+		        "Backup/remove this dir and restart to generate updated config file.\n"
+		        "---");
+		return old_conf_path;
+	}
+
+	if (!CreateDirectories(conf_path)) {
+		LOG_MSG("ERROR: Directory '%s' cannot be created",
+		        conf_path.c_str());
+		return old_conf_path;
+	}
+
+	return conf_path;
+}
+
+#endif // !WIN32
+
+void CROSS_DetermineConfigPaths()
+{
+#if !defined(WIN32) && !defined(MACOSX)
+	if (cached_conf_path.empty())
+		cached_conf_path = DetermineConfigPath();
+#endif
+}
+
 #ifdef WIN32
 static void W32_ConfDir(std::string& in,bool create) {
 	int c = create?1:0;
@@ -63,10 +145,11 @@ void Cross::GetPlatformConfigDir(std::string& in) {
 	in = "~/Library/Preferences";
 	ResolveHomedir(in);
 #else
-	in = "~/.dosbox";
-	ResolveHomedir(in);
+	assert(!cached_conf_path.empty());
+	in = cached_conf_path;
 #endif
-	in += CROSS_FILESPLIT;
+	if (in.back() != CROSS_FILESPLIT)
+		in += CROSS_FILESPLIT;
 }
 
 void Cross::GetPlatformConfigName(std::string& in) {
@@ -80,7 +163,8 @@ void Cross::GetPlatformConfigName(std::string& in) {
 	in = DEFAULT_CONFIG_FILE;
 }
 
-void Cross::CreatePlatformConfigDir(std::string& in) {
+void Cross::CreatePlatformConfigDir(std::string &in)
+{
 #ifdef WIN32
 	W32_ConfDir(in,true);
 	in += "\\DOSBox";
@@ -90,11 +174,12 @@ void Cross::CreatePlatformConfigDir(std::string& in) {
 	ResolveHomedir(in);
 	//Don't create it. Assume it exists
 #else
-	in = "~/.dosbox";
-	ResolveHomedir(in);
-	mkdir(in.c_str(),0700);
+	assert(!cached_conf_path.empty());
+	in = cached_conf_path.c_str();
+	mkdir(in.c_str(), 0700);
 #endif
-	in += CROSS_FILESPLIT;
+	if (in.back() != CROSS_FILESPLIT)
+		in += CROSS_FILESPLIT;
 }
 
 void Cross::ResolveHomedir(std::string & temp_line) {
@@ -300,5 +385,3 @@ FILE *fopen_wrap(const char *path, const char *mode) {
 
 	return fopen(path,mode);
 }
-
-