save categories that were used in the XML

Author: 3nids

src/app/qgisapp.cpp

@@ -8884,6 +8884,7 @@ void QgisApp::copyStyle( QgsMapLayer *sourceLayer, QgsMapLayer::StyleCategories
     }
     // Copies data in text form as well, so the XML can be pasted into a text editor
     clipboard()->setData( QGSCLIPBOARD_STYLE_MIME, doc.toByteArray(), doc.toString() );
+
     // Enables the paste menu element
     mActionPasteStyle->setEnabled( true );
   }

src/core/qgsmaplayer.cpp

@@ -551,6 +551,11 @@ bool QgsMapLayer::writeLayerXml( QDomElement &layerElement, QDomDocument &docume
 void QgsMapLayer::writeCommonStyle( QDomElement &layerElement, QDomDocument &document,
                                     const QgsReadWriteContext &context, QgsMapLayer::StyleCategories categories ) const
 {
+  // save categories
+  QMetaEnum metaEnum = QMetaEnum::fromType<QgsMapLayer::StyleCategories>();
+  QString categoriesKeys( metaEnum.valueToKeys( static_cast<int>( categories ) ) );
+  layerElement.setAttribute( QStringLiteral( "style_categories" ), categoriesKeys );
+
   if ( categories.testFlag( Rendering ) )
   {
     // use scale dependent visibility flag