Changing QgsProcessingParameterVectorDestination output to *.shp instead of *.gpkg in QGIS Processing Algorithm

Question

I'm updating a plugin for QGIS and struggling to see how to set the default file type when using the QgsProcessingParameterVectorDestination parameter. See code below.

    self.addParameter(
        QgsProcessingParameterVectorDestination(
            "OUTPUT_POND_OUTLINES",
            "Output Pond Outlines Vector",                
            optional=False,                
        )
    )

Based on the docs i can not see how to pass *.shp as the default format like you do with a QgsProcessingParameterFileDestination

    self.addParameter(
        QgsProcessingParameterFileDestination(
            "OUTPUT_POND_OUTLINES",
            "Output Pond Outlines Vector",                
            optional=False,
            fileFilter="ESRI Shapefile (*.shp)"                              
        )
    )

P.S. I prefer using QgsProcessingParameterVectorDestination as it handles the temporary output and adding to the current project by default. Where as QgsProcessingParameterFileDestination doesn't seem to have this capability.

Answer 1

As a workaround I can suggest the following approach:

Firstly initiate a "new" class e.g. QgsProcessingParameterVectorDestinationSHP with createFileFilter method in the processing script:

class QgsProcessingParameterVectorDestinationSHP(QgsProcessingParameterVectorDestination):
    def createFileFilter(self):
        return "ESRI Shapefile (*.shp)"

And then wrap the desired parameter into QgsProcessingParameterVectorDestinationSHP inside the def initAlgorithm(self, config=None):

self.addParameter(
    QgsProcessingParameterVectorDestinationSHP(
        name="OUTPUT_POND_OUTLINES",
        description="Output Pond Outlines Vector",                
        optional=False,
    )
)

After that it should work as intended:

And as was suggested by @IanTurton it is better switching to something more up-to-date i.e. GeoPackage.