[calamares] Use XDG_{DATA,CONFIG}_DIRS as appropriate

- Use DATA for the qml and branding directories (looks for qml/
   and branding/<name>/ in those directories).
 - Use CONFIG for the global settings and module settings (looks
   for settings.conf and module/<name>/ in those directories).

FIXES #941

src/calamares/CalamaresApplication.cpp

@@ -145,6 +145,9 @@ qmlDirCandidates( bool assumeBuilddir )
     {
         if ( assumeBuilddir )
             qmlDirs << QDir::current().absoluteFilePath( "src/qml" );  // In build-dir
+        if ( CalamaresUtils::haveExtraDirs() )
+            for ( auto s : CalamaresUtils::extraDataDirs() )
+                qmlDirs << ( s + QML );
         qmlDirs << CalamaresUtils::appDataDir().absoluteFilePath( QML );
     }
 
@@ -164,6 +167,9 @@ settingsFileCandidates( bool assumeBuilddir )
     {
         if ( assumeBuilddir )
             settingsPaths << QDir::current().absoluteFilePath( settings );
+        if ( CalamaresUtils::haveExtraDirs() )
+            for ( auto s : CalamaresUtils::extraConfigDirs() )
+                settingsPaths << ( s + settings );
         settingsPaths << CMAKE_INSTALL_FULL_SYSCONFDIR "/calamares/settings.conf";  // String concat
         settingsPaths << CalamaresUtils::appDataDir().absoluteFilePath( settings );
     }
@@ -182,6 +188,9 @@ brandingFileCandidates( bool assumeBuilddir, const QString& brandingFilename )
     {
         if ( assumeBuilddir )
             brandingPaths << ( QDir::currentPath() + QStringLiteral( "/src/" ) + brandingFilename );
+        if ( CalamaresUtils::haveExtraDirs() )
+            for ( auto s : CalamaresUtils::extraDataDirs() )
+                brandingPaths << ( s + brandingFilename );
         brandingPaths << QDir( CMAKE_INSTALL_FULL_SYSCONFDIR "/calamares/" ).absoluteFilePath( brandingFilename );
         brandingPaths << CalamaresUtils::appDataDir().absoluteFilePath( brandingFilename);
     }

src/libcalamares/utils/CalamaresUtils.cpp

@@ -97,12 +97,23 @@ setAppDataDir( const QDir& dir )
     s_isAppDataDirOverridden = true;
 }
 
+/* Split $ENV{@p name} on :, append to @p l, making sure each ends in / */
+static void
+mungeEnvironment( QStringList& l, const char *name )
+{
+    for ( auto s : QString( qgetenv( name ) ).split(':') )
+        if ( s.endsWith( '/' ) )
+            l << s;
+        else
+            l << ( s + '/' );
+}
+
 void
 setXdgDirs()
 {
     s_haveExtraDirs = true;
-    s_extraConfigDirs.append( QString( qgetenv( "XDG_CONFIG_DIRS" ) ).split(':') );
+    mungeEnvironment( s_extraConfigDirs, "XDG_CONFIG_DIRS" );
-    s_extraDataDirs.append( QString( qgetenv( "XDG_DATA_DIRS" ) ).split(':') );
+    mungeEnvironment( s_extraDataDirs, "XDG_DATA_DIRS" );
 }
 
 QStringList
@@ -121,7 +132,11 @@ extraDataDirs()
     return QStringList();
 }
 
-
+bool
+haveExtraDirs()
+{
+    return s_haveExtraDirs && ( !s_extraConfigDirs.isEmpty() || !s_extraDataDirs.isEmpty() );
+}
 
 bool
 isAppDataDirOverridden()

src/libcalamares/utils/CalamaresUtils.h

@@ -80,10 +80,13 @@ namespace CalamaresUtils
     DLLEXPORT void setQmlModulesDir( const QDir& dir );
 
     /** @brief Setup extra config and data dirs from the XDG variables.
-     *
      */
     DLLEXPORT void setXdgDirs();
+    /** @brief Are any extra directories configured? */
+    DLLEXPORT bool haveExtraDirs();
+    /** @brief XDG_CONFIG_DIRS, each guaranteed to end with / */
     DLLEXPORT QStringList extraConfigDirs();
+    /** @brief XDG_DATA_DIRS, each guaranteed to end with / */
     DLLEXPORT QStringList extraDataDirs();
 
     /**

src/libcalamaresui/modulesystem/Module.cpp

@@ -155,6 +155,10 @@ moduleConfigurationCandidates( bool assumeBuildDir, const QString& moduleName, c
         if ( assumeBuildDir && configFileName.contains( '/' ) )
             paths << QDir().absoluteFilePath( configFileName );
 
+        if ( CalamaresUtils::haveExtraDirs() )
+            for ( auto s : CalamaresUtils::extraConfigDirs() )
+                paths << ( s + QString( "modules/%1" ).arg( configFileName ) );
+
         paths << QString( "/etc/calamares/modules/%1" ).arg( configFileName );
         paths << CalamaresUtils::appDataDir().absoluteFilePath( QString( "modules/%1" ).arg( configFileName ) );
     }