[libcalamares] Another convenience config-extraction function

src/libcalamares/utils/CalamaresUtils.cpp

@@ -340,6 +340,18 @@ getBool( const QVariantMap& map, const QString& key, bool d )
     return result;
 }
 
+QString
+getString(const QVariantMap& map, const QString& key)
+{
+    if ( map.contains( key ) )
+    {
+        auto v = map.value( key );
+        if ( v.type() == QVariant::String )
+            return v.toString();
+    }
+    return QString();
+}
+
 QVariantMap
 getSubMap( const QVariantMap& map, const QString& key, bool& success )
 {

src/libcalamares/utils/CalamaresUtils.h

@@ -104,6 +104,11 @@ namespace CalamaresUtils
      */
     DLLEXPORT bool getBool( const QVariantMap& map, const QString& key, bool d );
 
+    /**
+     * Get a string value from a mapping; returns empty QString if no value.
+     */
+    DLLEXPORT QString getString( const QVariantMap& map, const QString& key );
+
     /**
      * Returns a sub-map (i.e. a nested map) from the given mapping with the
      * given key. @p success is set to true if the @p key exists