QgsRasterFileWriter: improve error reporting

python/core/auto_generated/raster/qgsrasterfilewritertask.sip.in

@@ -71,6 +71,17 @@ parameter indicates the file path for the written file(s).
 %Docstring
 Emitted when an error occurs which prevented the file being written (or if
 the task is canceled). The writing ``error`` will be reported.
+
+.. deprecated:: since QGIS 3.10. Use errorOccurred(int, const QString&)
+%End
+
+    void errorOccurred( int error, const QString &errorMessage );
+%Docstring
+Emitted when an error occurs which prevented the file being written (or if
+the task is canceled). The writing ``error`` will be reported and a
+``errorMessage`` will be potentially set.
+
+.. versionadded:: 3.10
 %End
 
   protected:

src/app/qgisapp.cpp

@@ -7816,12 +7816,24 @@ QString QgisApp::saveAsRasterFile( QgsRasterLayer *rasterLayer, const bool defau
   } );
 
   // when an error occurs:
-  connect( writerTask, &QgsRasterFileWriterTask::errorOccurred, this, [ = ]( int error )
+  connect( writerTask, qgis::overload< int, const QString &>::of( &QgsRasterFileWriterTask::errorOccurred ), this, [ = ]( int error, const QString & errorMessage )
   {
     if ( error != QgsRasterFileWriter::WriteCanceled )
     {
+      QString errorCodeStr;
+      if ( error == QgsRasterFileWriter::SourceProviderError )
+        errorCodeStr = tr( "source provider" );
+      else if ( error == QgsRasterFileWriter::DestProviderError )
+        errorCodeStr = tr( "destination provider" );
+      else if ( error == QgsRasterFileWriter::CreateDatasourceError )
+        errorCodeStr = tr( "data source creation" );
+      else if ( error == QgsRasterFileWriter::WriteError )
+        errorCodeStr = tr( "write error" );
+      QString fullErrorMsg( tr( "Cannot write raster. Error code: %1" ).arg( errorCodeStr ) );
+      if ( !errorMessage.isEmpty() )
+        fullErrorMsg += "\n" + errorMessage;
       QMessageBox::warning( this, tr( "Save Raster" ),
-                            tr( "Cannot write raster. Error code: %1" ).arg( error ),
+                            fullErrorMsg,
                             QMessageBox::Ok );
     }
   } );

src/core/raster/qgsrasterfilewriter.cpp

@@ -323,16 +323,28 @@ QgsRasterFileWriter::WriterError QgsRasterFileWriter::writeDataRaster( const Qgs
       }
       if ( !destProvider->isValid() )
       {
+        if ( feedback && !destProvider->error().isEmpty() )
+        {
+          feedback->appendError( destProvider->error().summary() );
+        }
         return CreateDatasourceError;
       }
       if ( nCols != destProvider->xSize() || nRows != destProvider->ySize() )
       {
         QgsDebugMsg( QStringLiteral( "Created raster does not have requested dimensions" ) );
+        if ( feedback )
+        {
+          feedback->appendError( QObject::tr( "Created raster does not have requested dimensions" ) );
+        }
         return CreateDatasourceError;
       }
       if ( nBands != destProvider->bandCount() )
       {
         QgsDebugMsg( QStringLiteral( "Created raster does not have requested band count" ) );
+        if ( feedback )
+        {
+          feedback->appendError( QObject::tr( "Created raster does not have requested band count" ) );
+        }
         return CreateDatasourceError;
       }
       if ( nBands )
@@ -583,21 +595,37 @@ QgsRasterFileWriter::WriterError QgsRasterFileWriter::writeImageRaster( QgsRaste
     }
     if ( !destProvider->isValid() )
     {
+      if ( feedback && !destProvider->error().isEmpty() )
+      {
+        feedback->appendError( destProvider->error().summary() );
+      }
       return CreateDatasourceError;
     }
     if ( nCols != destProvider->xSize() || nRows != destProvider->ySize() )
     {
       QgsDebugMsg( QStringLiteral( "Created raster does not have requested dimensions" ) );
+      if ( feedback )
+      {
+        feedback->appendError( QObject::tr( "Created raster does not have requested dimensions" ) );
+      }
       return CreateDatasourceError;
     }
     if ( nOutputBands != destProvider->bandCount() )
     {
       QgsDebugMsg( QStringLiteral( "Created raster does not have requested band count" ) );
+      if ( feedback )
+      {
+        feedback->appendError( QObject::tr( "Created raster does not have requested band count" ) );
+      }
       return CreateDatasourceError;
     }
     if ( Qgis::Byte != destProvider->dataType( 1 ) )
     {
       QgsDebugMsg( QStringLiteral( "Created raster does not have requested data type" ) );
+      if ( feedback )
+      {
+        feedback->appendError( QObject::tr( "Created raster does not have requested data type" ) );
+      }
       return CreateDatasourceError;
     }
   }

src/core/raster/qgsrasterfilewritertask.cpp

@@ -66,7 +66,13 @@ void QgsRasterFileWriterTask::finished( bool result )
   if ( result )
     emit writeComplete( mWriter.outputUrl() );
   else
+  {
     emit errorOccurred( mError );
+    QString errorMsg;
+    if ( !mFeedback->errors().isEmpty() )
+      errorMsg = mFeedback->errors().front();
+    emit errorOccurred( mError, errorMsg );
+  }
 }
 
 

src/core/raster/qgsrasterfilewritertask.h

@@ -81,9 +81,18 @@ class CORE_EXPORT QgsRasterFileWriterTask : public QgsTask
     /**
      * Emitted when an error occurs which prevented the file being written (or if
      * the task is canceled). The writing \a error will be reported.
+     * \deprecated since QGIS 3.10. Use errorOccurred(int, const QString&)
      */
     void errorOccurred( int error );
 
+    /**
+     * Emitted when an error occurs which prevented the file being written (or if
+     * the task is canceled). The writing \a error will be reported and a
+     * \a errorMessage will be potentially set.
+     * \since QGIS 3.10
+     */
+    void errorOccurred( int error, const QString &errorMessage );
+
   protected:
 
     bool run() override;
@@ -105,7 +114,6 @@ class CORE_EXPORT QgsRasterFileWriterTask : public QgsTask
     QgsRasterFileWriter::WriterError mError = QgsRasterFileWriter::NoError;
 
     QgsCoordinateTransformContext mTransformContext;
-
 };
 
 #endif //QGSRASTERFILEWRITERTASK_H