[calamares] Add option to obey XDG dirs

- Prep-work for #941
 - This does nothing, yet, just sets the stage for using
   XDG_CONFIG_DIRS and XDG_DATA_DIRS as well as the regular
   directories.

src/calamares/main.cpp

@@ -44,6 +44,8 @@ handle_args( CalamaresApplication& a )
                                           "Verbose output for debugging purposes (0-8).", "level" );
     QCommandLineOption configOption( QStringList{ "c", "config"},
                                      "Configuration directory to use, for testing purposes.", "config" );
+    QCommandLineOption xdgOption( QStringList{"X", "xdg-config"},
+                                  "Use XDG_{CONFIG,DATA}_DIRS as well." );
 
     QCommandLineParser parser;
     parser.setApplicationDescription( "Distribution-independent installer framework" );
@@ -53,6 +55,7 @@ handle_args( CalamaresApplication& a )
     parser.addOption( debugOption );
     parser.addOption( debugLevelOption );
     parser.addOption( configOption );
+    parser.addOption( xdgOption );
 
     parser.process( a );
 
@@ -72,6 +75,8 @@ handle_args( CalamaresApplication& a )
     }
     if ( parser.isSet( configOption ) )
         CalamaresUtils::setAppDataDir( QDir( parser.value( configOption ) ) );
+    if ( parser.isSet( xdgOption ) )
+        CalamaresUtils::setXdgDirs();
 }
 
 int

src/libcalamares/utils/CalamaresUtils.cpp

@@ -49,6 +49,9 @@ static QTranslator* s_brandingTranslator = nullptr;
 static QTranslator* s_translator = nullptr;
 static QString s_translatorLocaleName;
 
+static bool s_haveExtraDirs = false;
+static QStringList s_extraConfigDirs;
+static QStringList s_extraDataDirs;
 
 static bool
 isWritableDir( const QDir& dir )
@@ -94,6 +97,31 @@ setAppDataDir( const QDir& dir )
     s_isAppDataDirOverridden = true;
 }
 
+void
+setXdgDirs()
+{
+    s_haveExtraDirs = true;
+    s_extraConfigDirs.append( QString( qgetenv( "XDG_CONFIG_DIRS" ) ).split(':') );
+    s_extraDataDirs.append( QString( qgetenv( "XDG_DATA_DIRS" ) ).split(':') );
+}
+
+QStringList
+extraConfigDirs()
+{
+    if ( s_haveExtraDirs )
+        return s_extraConfigDirs;
+    return QStringList();
+}
+
+QStringList
+extraDataDirs()
+{
+    if ( s_haveExtraDirs )
+        return s_extraDataDirs;
+    return QStringList();
+}
+
+
 
 bool
 isAppDataDirOverridden()

src/libcalamares/utils/CalamaresUtils.h

@@ -79,6 +79,13 @@ namespace CalamaresUtils
 
     DLLEXPORT void setQmlModulesDir( const QDir& dir );
 
+    /** @brief Setup extra config and data dirs from the XDG variables.
+     *
+     */
+    DLLEXPORT void setXdgDirs();
+    DLLEXPORT QStringList extraConfigDirs();
+    DLLEXPORT QStringList extraDataDirs();
+
     /**
      * @brief removeDiacritics replaces letters with diacritics and ligatures with
      * alternative forms and digraphs.