Don't crash when writing invalid variants via QgsXmlUtils

Author: nyalldawson

src/core/qgsxmlutils.cpp

@@ -105,6 +105,12 @@ QDomElement QgsXmlUtils::writeVariant( const QVariant &value, QDomDocument &doc
   QDomElement element = doc.createElement( QStringLiteral( "Option" ) );
   switch ( value.type() )
   {
+    case QVariant::Invalid:
+    {
+      element.setAttribute( QStringLiteral( "type" ), QStringLiteral( "invalid" ) );
+      break;
+    }
+
     case QVariant::Map:
     {
       QVariantMap map = value.toMap();
@@ -166,7 +172,7 @@ QDomElement QgsXmlUtils::writeVariant( const QVariant &value, QDomDocument &doc
     }
 
     default:
-      Q_ASSERT_X( false, "QgsXmlUtils::writeVariant", "unsupported variant type" );
+      Q_ASSERT_X( false, "QgsXmlUtils::writeVariant", QStringLiteral( "unsupported variant type %1" ).arg( QVariant::typeToName( value.type() ) ).toLocal8Bit() );
       break;
   }
 
@@ -177,7 +183,11 @@ QVariant QgsXmlUtils::readVariant( const QDomElement &element )
 {
   QString type = element.attribute( QStringLiteral( "type" ) );
 
-  if ( type == QLatin1String( "int" ) )
+  if ( type == QLatin1String( "invalid" ) )
+  {
+    return QVariant();
+  }
+  else if ( type == QLatin1String( "int" ) )
   {
     return element.attribute( QStringLiteral( "value" ) ).toInt();
   }

tests/src/python/test_qgsxmlutils.py

@@ -27,6 +27,17 @@
 
 class TestQgsXmlUtils(unittest.TestCase):
 
+    def test_invalid(self):
+        """
+        Test that invalid attributes are correctly loaded and written
+        """
+        doc = QDomDocument("properties")
+
+        elem = QgsXmlUtils.writeVariant(None, doc)
+
+        prop2 = QgsXmlUtils.readVariant(elem)
+        self.assertIsNone(prop2)
+
     def test_integer(self):
         """
         Test that maps are correctly loaded and written