[processing] ensure that outputs of vector overlay operations are multiparts (#3622)

Author: nirvn

python/plugins/processing/algs/qgis/Clip.py

@@ -67,7 +67,7 @@ def processAlgorithm(self, progress):
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
             source_layer.fields(),
-            source_layer.wkbType(),
+            QgsWkbTypes.multiType(source_layer.wkbType()),
             source_layer.crs())
 
         # first build up a list of clip geometries

python/plugins/processing/algs/qgis/Difference.py

@@ -69,7 +69,7 @@ def processAlgorithm(self, progress):
             self.getParameterValue(Difference.OVERLAY))
         ignoreInvalid = self.getParameterValue(Difference.IGNORE_INVALID)
 
-        geomType = layerA.wkbType()
+        geomType = QgsWkbTypes.multiType(layerA.wkbType())
         writer = self.getOutputFromName(
             Difference.OUTPUT).getVectorWriter(layerA.fields(),
                                                geomType,

python/plugins/processing/algs/qgis/Intersection.py

@@ -75,7 +75,7 @@ def processAlgorithm(self, progress):
         vlayerB = dataobjects.getObjectFromUri(
             self.getParameterValue(self.INPUT2))
 
-        geomType = vlayerA.wkbType()
+        geomType = QgsWkbTypes.multiType(vlayerA.wkbType())
         fields = vector.combineVectorFields(vlayerA, vlayerB)
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields,
                                                                      geomType, vlayerA.crs())

python/plugins/processing/algs/qgis/SymmetricalDifference.py

@@ -65,7 +65,7 @@ def processAlgorithm(self, progress):
         layerB = dataobjects.getObjectFromUri(
             self.getParameterValue(self.OVERLAY))
 
-        geomType = layerA.wkbType()
+        geomType = QgsWkbTypes.multiType(layerA.wkbType())
         fields = vector.combineVectorFields(layerA, layerB)
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
             fields, geomType, layerA.crs())