[PATCH] Follow XDG Base Directory spec on Linux

Uses QStandardPaths to get cache, data and config XDG folders.
The config file go to $XDG_CONFIG_HOME/hydrogen/hydrogen.conf
The cache folder go to $XDG_CACHE_HOME/hydrogen/
And all the data subfolders (drumkits, plugins, playlists, etc.) go to
$XDG_DATA_HOME/hydrogen/ along with the hydrogen.log file.

If old folder (~/.hydrogen/) is found, use that instead of the XDG paths.

The __usr_*_paths are setted outside a function, so QStandardPaths isn't
avaliable to get the XDG paths. Also no APPNAME is avaliable until
setApplicationName() is called after the Filesystem::check_usr_paths()
is used. To avoid this update_usr_paths() is added at the begining of
check_usr_paths() to update the correct values from QStandardPaths.

src/core/Helpers/Filesystem.cpp

@@ -31,6 +31,10 @@
 #include <QtCore/QFileInfo>
 #include <QtCore/QCoreApplication>
 #include <QDateTime>
+#if defined(Q_OS_MACX) || defined(WIN32)
+#else
+#include <QStandardPaths>
+#endif
 
 #ifdef H2CORE_HAVE_OSC
 #include <core/NsmClient.h>
@@ -100,14 +104,16 @@ const QString Filesystem::playlists_filter_name = "Hydrogen Playlists (*.h2playl
 
 QString Filesystem::__sys_data_path;
 QString Filesystem::__usr_data_path;
+QString Filesystem::__usr_cache_path;
 QString Filesystem::__usr_cfg_path;
 
 #ifdef Q_OS_MACX
 	QString Filesystem::__usr_log_path =QDir::homePath().append( "/Library/Application Support/Hydrogen/" LOG_FILE );
 #elif WIN32
 	QString Filesystem::__usr_log_path = QDir::homePath().append( "/.hydrogen/" LOG_FILE );
 #else
-	QString Filesystem::__usr_log_path = QDir::homePath().append( "/" H2_USR_PATH "/" LOG_FILE);
+	QString Filesystem::__usr_log_path = QDir::homePath().append( "/" H2_USR_PATH "/" );
+	bool __usr_log_path_initialized = false;
 #endif
 
 
@@ -412,9 +418,36 @@ bool Filesystem::check_sys_paths()
 }
 
 
+#if defined(Q_OS_MACX) || defined(WIN32)
+#else
+void Filesystem::update_usr_paths()
+{
+	// If the old path exists (e.g. ~/.hydrogen), old path is used; else uses
+	// QStandardPaths to get XDG Paths on Linux.
+	if ( !QFileInfo::exists( QFileInfo(__usr_cfg_path).absolutePath() ) )
+	{
+		__usr_cfg_path = QStandardPaths::writableLocation(
+				QStandardPaths::AppConfigLocation).append("/" USR_CONFIG);
+		__usr_data_path = QStandardPaths::writableLocation(
+				QStandardPaths::AppLocalDataLocation).append("/");
+		__usr_cache_path = QStandardPaths::writableLocation(
+				QStandardPaths::CacheLocation).append("/");
+	} else {
+		__usr_cache_path = __usr_data_path + CACHE;
+	}
+}
+#endif
+
+
 bool Filesystem::check_usr_paths()
 {
 	bool ret = true;
+
+#if defined(Q_OS_MACX) || defined(WIN32)
+#else
+	update_usr_paths();
+	if ( !path_usable( QFileInfo(__usr_cfg_path).absolutePath() ) ) ret = false;
+#endif
 	if( !path_usable( tmp_dir() ) ) ret = false;
 	if( !path_usable( __usr_data_path ) ) ret = false;
 	if( !path_usable( cache_dir() ) ) ret = false;
@@ -518,6 +551,20 @@ QString Filesystem::playlist_xsd_path( )
 }
 QString Filesystem::log_file_path()
 {
+#if defined(Q_OS_MACX) || defined(WIN32)
+#else
+	if ( !__usr_log_path_initialized )
+	{
+		if ( !QFileInfo::exists( __usr_log_path ) )
+		{
+			__usr_log_path = QStandardPaths::writableLocation(
+					QStandardPaths::AppLocalDataLocation).append( "/" LOG_FILE );
+		} else {
+			__usr_log_path.append( LOG_FILE );
+		}
+		__usr_log_path_initialized = true;
+	}
+#endif
 	return __usr_log_path;
 }
 
@@ -592,11 +639,19 @@ QString Filesystem::playlist_path( const QString& pl_name )
 }
 QString Filesystem::cache_dir()
 {
+#if defined(Q_OS_MACX) || defined(WIN32)
 	return __usr_data_path + CACHE;
+#else
+	return __usr_cache_path;
+#endif
 }
 QString Filesystem::repositories_cache_dir()
 {
+#if defined(Q_OS_MACX) || defined(WIN32)
 	return __usr_data_path + CACHE + REPOSITORIES;
+#else
+	return __usr_cache_path + REPOSITORIES;
+#endif
 }
 QString Filesystem::demos_dir()
 {

src/core/Helpers/Filesystem.h

@@ -446,6 +446,12 @@ namespace H2Core
 		 */
 		static bool check_permissions( const QString& path, const int perms, bool silent );
 
+		/**
+		 * Update the data, config and cache paths with QStandardPaths if old
+		 * folder doesn't exist (e.g. ~/.hydrogen/).
+		 */
+		static void update_usr_paths();
+
 		/**
 		 * Path to the system files set in Filesystem::bootstrap().
 		 *
@@ -471,6 +477,7 @@ namespace H2Core
 		 */
 		static QString __sys_data_path;     ///< the path to the system files
 		static QString __usr_data_path;     ///< the path to the user files
+		static QString __usr_cache_path;    ///< the path to the cache files
 		static QString __usr_cfg_path;      ///< the path to the user config file
 		static QString __usr_log_path;      ///< the path to the log file
 		static QStringList __ladspa_paths;  ///< paths to laspa plugins