Store original style as QDomDocument instead of an XML string

python/core/auto_generated/qgsmaplayer.sip.in

@@ -1237,7 +1237,7 @@ Returns true if the refresh on provider nofification is enabled
 .. versionadded:: 3.0
 %End
 
-    QString originalXmlProperties() const;
+    QDomDocument originalXmlProperties() const;
 %Docstring
 Returns the XML properties of the original layer as they were when the layer
 was first read from the project file. In case of new layers this is normally empty.
@@ -1247,7 +1247,7 @@ The storage format for the XML is qlr
 .. versionadded:: 3.6
 %End
 
-    void setOriginalXmlProperties( const QString &originalXmlProperties );
+    void setOriginalXmlProperties( const QDomDocument &originalXmlProperties );
 %Docstring
 Sets the original XML properties for the layer to  ``originalXmlProperties``
 

src/app/qgisapp.cpp

@@ -6955,26 +6955,17 @@ void QgisApp::changeDataSource( QgsMapLayer *layer )
       bool layerIsValid( layer->isValid() );
       layer->setDataSource( uri.uri, layer->name(), uri.providerKey, QgsDataProvider::ProviderOptions() );
       // Re-apply style
-      if ( !( layerIsValid || layer->originalXmlProperties().isEmpty() ) )
+      if ( !( layerIsValid || layer->originalXmlProperties().isNull() ) )
       {
         QgsReadWriteContext context;
         context.setPathResolver( QgsProject::instance()->pathResolver() );
         context.setProjectTranslator( QgsProject::instance() );
         QString errorMsg;
-        QDomDocument doc;
-        if ( doc.setContent( layer->originalXmlProperties() ) )
+        QDomDocument doc( layer->originalXmlProperties() );
+        QDomNode layer_node( doc.firstChild( ) );
+        if ( ! layer->readSymbology( layer_node, errorMsg, context ) )
         {
-          QDomNode layer_node( doc.firstChild( ) );
-          if ( ! layer->readSymbology( layer_node, errorMsg, context ) )
-          {
-            QgsDebugMsg( QStringLiteral( "Failed to restore original layer style from stored XML for layer %1: %2" )
-                         .arg( layer->name( ) )
-                         .arg( errorMsg ) );
-          }
-        }
-        else
-        {
-          QgsDebugMsg( QStringLiteral( "Failed to create XML QDomDocument for layer %1: %2" )
+          QgsDebugMsg( QStringLiteral( "Failed to restore original layer style from stored XML for layer %1: %2" )
                        .arg( layer->name( ) )
                        .arg( errorMsg ) );
         }

src/core/layertree/qgslayertreeutils.cpp

@@ -329,10 +329,7 @@ void QgsLayerTreeUtils::storeOriginalLayersProperties( QgsLayerTreeGroup *group,
             QDomDocument document( documentType );
             QDomElement element = mlNode.toElement();
             document.appendChild( element );
-            QString str;
-            QTextStream stream( &str );
-            document.save( stream, 4 /*indent*/ );
-            l->setOriginalXmlProperties( str );
+            l->setOriginalXmlProperties( document );
           }
         }
       }

src/core/qgsmaplayer.cpp

@@ -1833,12 +1833,12 @@ bool QgsMapLayer::isReadOnly() const
   return true;
 }
 
-QString QgsMapLayer::originalXmlProperties() const
+QDomDocument QgsMapLayer::originalXmlProperties() const
 {
   return mOriginalXmlProperties;
 }
 
-void QgsMapLayer::setOriginalXmlProperties( const QString &originalXmlProperties )
+void QgsMapLayer::setOriginalXmlProperties( const QDomDocument &originalXmlProperties )
 {
   mOriginalXmlProperties = originalXmlProperties;
 }

src/core/qgsmaplayer.h

@@ -1109,7 +1109,7 @@ class CORE_EXPORT QgsMapLayer : public QObject
      *
      * \since QGIS 3.6
      */
-    QString originalXmlProperties() const;
+    QDomDocument originalXmlProperties() const;
 
     /**
      * Sets the original XML properties for the layer to  \a originalXmlProperties
@@ -1118,7 +1118,7 @@ class CORE_EXPORT QgsMapLayer : public QObject
      *
      * \since QGIS 3.6
      */
-    void setOriginalXmlProperties( const QString &originalXmlProperties );
+    void setOriginalXmlProperties( const QDomDocument &originalXmlProperties );
 
   public slots:
 
@@ -1529,7 +1529,7 @@ class CORE_EXPORT QgsMapLayer : public QObject
      *
      * This information can be used to pass through the bad layers or to reset changes on a good layer
      */
-    QString mOriginalXmlProperties;
+    QDomDocument mOriginalXmlProperties;
 
 };
 

src/core/qgsproject.cpp

@@ -1774,17 +1774,10 @@ bool QgsProject::writeProjectFile( const QString &filename )
           maplayerElem = doc->createElement( QStringLiteral( "maplayer" ) );
           ml->writeLayerXml( maplayerElem, *doc, context );
         }
-        else if ( ! ml->originalXmlProperties().isEmpty() )
+        else if ( ! ml->originalXmlProperties().isNull() )
         {
-          QDomDocument document;
-          if ( document.setContent( ml->originalXmlProperties() ) )
-          {
-            maplayerElem = document.firstChildElement();
-          }
-          else
-          {
-            QgsDebugMsg( QStringLiteral( "Could not restore layer properties for layer %1" ).arg( ml->id() ) );
-          }
+          QDomDocument document( ml->originalXmlProperties() );
+          maplayerElem = document.firstChildElement();
         }
 
         emit writeMapLayer( ml, maplayerElem, *doc );

tests/src/python/test_qgsprojectbadlayers.py

@@ -35,6 +35,7 @@
 from qgis.PyQt.QtGui import QFont, QColor
 from qgis.PyQt.QtTest import QSignalSpy
 from qgis.PyQt.QtCore import QT_VERSION_STR, QTemporaryDir, QSize
+from qgis.PyQt.QtXml import QDomDocument, QDomNode, QDomImplementation
 
 from qgis.testing import start_app, unittest
 from utilities import (unitTestDataPath, renderMapToImage)
@@ -99,8 +100,12 @@ def test_project_roundtrip(self):
         self.assertTrue(raster.originalXmlProperties() != '')
         self.assertTrue(raster_copy.originalXmlProperties() != '')
         # Test setter
-        raster.setOriginalXmlProperties('pippo')
-        self.assertEqual(raster.originalXmlProperties(), 'pippo')
+        domimp = QDomImplementation()
+        documentType = domimp.createDocumentType("qgis", "http://mrcc.com/qgis.dtd", "SYSTEM")
+        document = QDomDocument(documentType)
+        document.setContent("<pippo>pluto</pippo>")
+        raster.setOriginalXmlProperties(document)
+        self.assertEqual(raster.originalXmlProperties(), document)
 
         # Now create and invalid project:
         bad_project_path = os.path.join(temp_dir.path(), 'project_bad.qgs')
@@ -144,7 +149,7 @@ def test_project_roundtrip(self):
         self.assertTrue(raster_copy.isValid())
 
     def test_project_relations(self):
-        """Tests that a project with bad layers and relations can be saved with relations"""
+        """Tests that a project with bad layers and relations can be maintained"""
 
         temp_dir = QTemporaryDir()
         p = QgsProject.instance()
@@ -235,7 +240,6 @@ def testStyles(self):
         p = QgsProject.instance()
         project_path = os.path.join(temp_dir.path(), 'good_layers_test.qgs')
         copyfile(os.path.join(TEST_DATA_DIR, 'projects', 'good_layers_test.qgs'), project_path)
-        copyfile(os.path.join(TEST_DATA_DIR, 'projects', 'bad_layers_test.gpkg'), os.path.join(temp_dir.path(), 'bad_layers_test.gpkg'))
         for f in (
                 'bad_layer_raster_test.tfw',
                 'bad_layer_raster_test.tiff',