Linux: implement relative installation

When setting an empty updater.conf next to the updater executable,
the folder containing the updater executable is used to install
the game.

Author: illwieckz

linux.cpp

@@ -112,6 +112,17 @@ void migrateHomePath()
     }
 }
 
+QString relativeInstallPath()
+{
+	QFileInfo applicationFileInfo(QCoreApplication::applicationFilePath());
+    QString applicationDirectory = applicationFileInfo.absolutePath();
+    QFile configurationFile(applicationDirectory + "/updater.conf");
+    if (configurationFile.exists()) {
+        return applicationDirectory;
+    }
+    return QString();
+}
+
 QString defaultInstallPath()
 {
     // if needed, migrate legacy homepath to prevent the updater
@@ -123,6 +134,10 @@ QString defaultInstallPath()
     // it returns "~/.local/share/unvanquished/updater"
     // and we want "~/.local/share/unvanquished/base"
     // game itself puts stuff in "~/.local/share/unvanquished"
+    QString relative = relativeInstallPath();
+    if (!relative.isNull()) {
+        return relative;
+    }
     return QStandardPaths::writableLocation(QStandardPaths::GenericDataLocation) + "/unvanquished/base";
 }
 
@@ -294,6 +309,10 @@ void initApplicationName()
 // Settings are stored in ~/.config/unvanquished/updater.conf
 QSettings* makePersistentSettings(QObject* parent)
 {
+    QString relative = relativeInstallPath();
+    if (!relative.isNull()) {
+        return new QSettings(relative, QSettings::NativeFormat, parent);
+    }
     return new QSettings(parent);
 }