bool QgsVectorLayerEditBuffer::commitChanges( QStringList &commitErrors )
{
  QgsVectorDataProvider *provider = L->dataProvider();
  commitErrors.clear();

  int cap = provider->capabilities();
  bool success = true;

  // geometry updates   attribute updates
  // yes                no                    => changeGeometryValues
  // no                 yes                   => changeAttributeValues
  // yes                yes                   => changeFeatures

  // to fix https://issues.qgis.org/issues/15741
  // first of all check if feature to add is compatible with provider type
  // this check have to be done before all checks to avoid to clear internal
  // buffer if some of next steps success.
  if ( success && !mAddedFeatures.isEmpty() )
  {
    if ( cap & QgsVectorDataProvider::AddFeatures )
    {
      if ( provider->doesStrictFeatureTypeCheck() )
      {
        for ( const auto &f : qgis::as_const( mAddedFeatures ) )
        {
          if ( ( ! f.hasGeometry() ) ||
               ( f.geometry().wkbType() == provider->wkbType() ) )
            continue;

          if ( provider->convertToProviderType( f.geometry() ).isNull() )
          {
            commitErrors << tr( "ERROR: %n feature(s) not added - geometry type is not compatible with the current layer.", "not added features count", mAddedFeatures.size() );
            success = false;
            break;
          }
        }
      }
    }
    else
    {
      commitErrors << tr( "ERROR: %n feature(s) not added - provider doesn't support adding features.", "not added features count", mAddedFeatures.size() );
      success = false;
    }
  }

  //
  // update geometries
  //
  if ( !mChangedGeometries.isEmpty() && ( ( cap & QgsVectorDataProvider::ChangeFeatures ) == 0 || mChangedAttributeValues.isEmpty() ) )
  {
    if ( provider->changeGeometryValues( mChangedGeometries ) )
    {
      commitErrors << tr( "SUCCESS: %n geometries were changed.", "changed geometries count", mChangedGeometries.size() );

      emit committedGeometriesChanges( L->id(), mChangedGeometries );
      mChangedGeometries.clear();
    }
    else
    {
      commitErrors << tr( "ERROR: %n geometries not changed.", "not changed geometries count", mChangedGeometries.size() );
      success = false;
    }
  }

  QgsFields oldFields = L->fields();

  //
  // delete attributes
  //
  bool attributesChanged = false;
  if ( !mDeletedAttributeIds.isEmpty() )
  {
    if ( ( cap & QgsVectorDataProvider::DeleteAttributes ) && provider->deleteAttributes( mDeletedAttributeIds.toSet() ) )
    {
      commitErrors << tr( "SUCCESS: %n attribute(s) deleted.", "deleted attributes count", mDeletedAttributeIds.size() );

      emit committedAttributesDeleted( L->id(), mDeletedAttributeIds );

      mDeletedAttributeIds.clear();
      attributesChanged = true;
    }
    else
    {
      commitErrors << tr( "ERROR: %n attribute(s) not deleted.", "not deleted attributes count", mDeletedAttributeIds.size() );
#if 0
      QString list = "ERROR: Pending attribute deletes:";
      Q_FOREACH ( int idx, mDeletedAttributeIds )
      {
        list.append( ' ' + L->fields().at( idx ).name() );
      }
      commitErrors << list;
#endif
      success = false;
    }
  }