[processing] When writing a layer to a temporary GPKG file for

compatibilty with provider's supported formats, rename the
existing FID column if we can't write the FID values into
the GPKG

Eg when the source layer has string/duplicate fids, we warn
the user and then automatically move the existing fids to
a "OLD_FID" field

src/core/processing/qgsprocessingutils.cpp

@@ -1350,7 +1350,7 @@ QString QgsProcessingUtils::formatHelpMapAsHtml( const QVariantMap &map, const Q
 }
 
 QString convertToCompatibleFormatInternal( const QgsVectorLayer *vl, bool selectedFeaturesOnly, const QString &baseName, const QStringList &compatibleFormats, const QString &preferredFormat, QgsProcessingContext &context, QgsProcessingFeedback *feedback, QString *layerName,
-    long long featureLimit, const QString &filterExpression )
+    long long featureLimit, const QString &filterExpression, bool renameFid )
 {
   bool requiresTranslation = false;
 
@@ -1412,7 +1412,14 @@ QString convertToCompatibleFormatInternal( const QgsVectorLayer *vl, bool select
     QgsVectorFileWriter::SaveVectorOptions saveOptions;
     saveOptions.fileEncoding = context.defaultEncoding();
     saveOptions.driverName = QgsVectorFileWriter::driverForExtension( preferredFormat );
-    std::unique_ptr< QgsVectorFileWriter > writer( QgsVectorFileWriter::create( temp, vl->fields(), vl->wkbType(), vl->crs(), context.transformContext(), saveOptions ) );
+    QgsFields fields = vl->fields();
+    if ( renameFid )
+    {
+      const int fidIndex = fields.lookupField( QStringLiteral( "fid" ) );
+      if ( fidIndex >= 0 )
+        fields.rename( fidIndex, QStringLiteral( "OLD_FID" ) );
+    }
+    std::unique_ptr< QgsVectorFileWriter > writer( QgsVectorFileWriter::create( temp, fields, vl->wkbType(), vl->crs(), context.transformContext(), saveOptions ) );
     QgsFeature f;
     QgsFeatureIterator it;
     QgsFeatureRequest request;
@@ -1439,10 +1446,19 @@ QString convertToCompatibleFormatInternal( const QgsVectorLayer *vl, bool select
 
       if ( !writer->addFeature( f, QgsFeatureSink::FastInsert ) && feedback )
       {
+        const QString errorMessage = writer->errorMessage();
+        if ( !renameFid && saveOptions.driverName == QLatin1String( "GPKG" ) && errorMessage.contains( "fid", Qt::CaseInsensitive ) )
+        {
+          // try again, dropping the FID field
+          feedback->reportError( QObject::tr( "Cannot store existing FID values in temporary GeoPackage layer, these will be moved to \"OLD_FID\" instead." ), false );
+          return convertToCompatibleFormatInternal( vl, selectedFeaturesOnly, baseName, compatibleFormats, preferredFormat, context, feedback, layerName,
+                 featureLimit, filterExpression, true );
+        }
+
         QString errorText;
         if ( errorCounter++ < maxErrors )
         {
-          errorText = QObject::tr( "Error writing feature # %1 to output layer: %2" ).arg( QString::number( f.id() ), writer->errorMessage() );
+          errorText = QObject::tr( "Error writing feature # %1 to output layer: %2" ).arg( QString::number( f.id() ), errorMessage );
 
           feedback->reportError( errorText );
         }
@@ -1462,13 +1478,13 @@ QString convertToCompatibleFormatInternal( const QgsVectorLayer *vl, bool select
 
 QString QgsProcessingUtils::convertToCompatibleFormat( const QgsVectorLayer *vl, bool selectedFeaturesOnly, const QString &baseName, const QStringList &compatibleFormats, const QString &preferredFormat, QgsProcessingContext &context, QgsProcessingFeedback *feedback, long long featureLimit, const QString &filterExpression )
 {
-  return convertToCompatibleFormatInternal( vl, selectedFeaturesOnly, baseName, compatibleFormats, preferredFormat, context, feedback, nullptr, featureLimit, filterExpression );
+  return convertToCompatibleFormatInternal( vl, selectedFeaturesOnly, baseName, compatibleFormats, preferredFormat, context, feedback, nullptr, featureLimit, filterExpression, false );
 }
 
 QString QgsProcessingUtils::convertToCompatibleFormatAndLayerName( const QgsVectorLayer *layer, bool selectedFeaturesOnly, const QString &baseName, const QStringList &compatibleFormats, const QString &preferredFormat, QgsProcessingContext &context, QgsProcessingFeedback *feedback, QString &layerName, long long featureLimit, const QString &filterExpression )
 {
   layerName.clear();
-  return convertToCompatibleFormatInternal( layer, selectedFeaturesOnly, baseName, compatibleFormats, preferredFormat, context, feedback, &layerName, featureLimit, filterExpression );
+  return convertToCompatibleFormatInternal( layer, selectedFeaturesOnly, baseName, compatibleFormats, preferredFormat, context, feedback, &layerName, featureLimit, filterExpression, false );
 }
 
 QgsFields QgsProcessingUtils::combineFields( const QgsFields &fieldsA, const QgsFields &fieldsB, const QString &fieldsBPrefix )

tests/src/analysis/testqgsprocessing.cpp

@@ -12672,11 +12672,18 @@ void TestQgsProcessing::convertCompatibleDuplicateFids()
   QVariantMap params;
   params.insert( QStringLiteral( "source" ), QgsProcessingFeatureSourceDefinition( layer->id(), false ) );
 
-  QgsProcessingParameters::parameterAsCompatibleSourceLayerPath( def.get(), params, context, QStringList() << "gpkg", QString( "gpkg" ), &feedback );
+  const QString temporaryFile = QgsProcessingParameters::parameterAsCompatibleSourceLayerPath( def.get(), params, context, QStringList() << "gpkg", QString( "gpkg" ), &feedback );
   const QStringList logs( feedback.textLog().split( '\n', Qt::SplitBehaviorFlags::SkipEmptyParts ) );
-  QCOMPARE( logs.size(), 11 );
-  QVERIFY( logs.first().startsWith( QLatin1String( "Error writing feature # 2" ) ) );
-  QVERIFY( logs.last().startsWith( QLatin1String( "There were 11 errors writing features" ) ) );
+  QCOMPARE( logs.size(), 1 );
+  QCOMPARE( logs.at( 0 ), QStringLiteral( "Cannot store existing FID values in temporary GeoPackage layer, these will be moved to \"OLD_FID\" instead." ) );
+
+  QgsVectorLayer vl( temporaryFile );
+  QVERIFY( vl.isValid() );
+
+  QCOMPARE( vl.featureCount(), 12 );
+  QCOMPARE( vl.fields().at( 0 ).name(), QStringLiteral( "fid" ) );
+  QCOMPARE( vl.fields().at( 1 ).name(), QStringLiteral( "OLD_FID" ) );
+  QCOMPARE( vl.fields().at( 2 ).name(), QStringLiteral( "name" ) );
 }
 
 void TestQgsProcessing::create()