read source from provider before saving memory layer (fixes #8997)

SebDieBln · jef-n · commit bc61f758e389 · 2016-01-15T11:41:27.000+01:00
(cherry picked from commit dbc0f07)
diff --git a/src/core/qgsmaplayer.cpp b/src/core/qgsmaplayer.cpp
@@ -46,6 +46,7 @@
 #include "qgsrasterlayer.h"
 #include "qgsrectangle.h"
 #include "qgsvectorlayer.h"
+#include "qgsvectordataprovider.h"
 
 
 QgsMapLayer::QgsMapLayer( QgsMapLayer::LayerType type,
@@ -559,6 +560,11 @@ bool QgsMapLayer::writeLayerXML( QDomElement& layerElement, QDomDocument& docume
     urlDest.setQueryItems( urlSource.queryItems() );
     src = QString::fromAscii( urlDest.toEncoded() );
   }
+  else if ( vlayer && vlayer->providerType() == "memory" )
+  {
+    // Refetch the source from the provider, because adding fields actually changes the source for this provider.
+    src = vlayer->dataProvider()->dataSourceUri();
+  }
   else
   {
     bool handled = false;
