Use QPointer for storing layer pointers in expression scope

Author: m-kuhn

src/core/qgsexpression.cpp

@@ -331,7 +331,8 @@ static QgsExpression::Node* getNode( const QVariant& value, QgsExpression* paren
 
 QgsVectorLayer* getVectorLayer( const QVariant& value, QgsExpression* )
 {
-  QgsVectorLayer* vl = value.value<QgsVectorLayer*>();
+  QgsMapLayer* ml = value.value< QPointer<QgsMapLayer> >().data();
+  QgsVectorLayer* vl = qobject_cast<QgsVectorLayer*>( ml );
   if ( !vl )
   {
     QString layerString = value.toString();

src/core/qgsexpressioncontext.cpp

@@ -691,7 +691,7 @@ QgsExpressionContextScope* QgsExpressionContextUtils::layerScope( const QgsMapLa
 
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layer_name" ), layer->name(), true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layer_id" ), layer->id(), true ) );
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layer" ), QVariant::fromValue<QgsMapLayer*>( const_cast<QgsMapLayer*>( layer ) ), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layer" ), QVariant::fromValue<QPointer<QgsMapLayer> >( QPointer<QgsMapLayer>( const_cast<QgsMapLayer*>( layer ) ) ), true ) );
 
   const QgsVectorLayer* vLayer = dynamic_cast< const QgsVectorLayer* >( layer );
   if ( vLayer )