Add minimal smartness for QgsProcessingFeatureSource::hasFeatures

python/core/auto_generated/processing/qgsprocessingutils.sip.in

@@ -260,6 +260,9 @@ An optional ``request`` can be used to optimise the returned
 iterator, eg by restricting the returned attributes or geometry.
 %End
 
+    virtual QgsFeatureSource::FeatureAvailability hasFeatures() const;
+
+
     virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest &request = QgsFeatureRequest() ) const;
 
     virtual QgsCoordinateReferenceSystem sourceCrs() const;

src/core/processing/qgsprocessingutils.cpp

@@ -721,6 +721,14 @@ QgsFeatureIterator QgsProcessingFeatureSource::getFeatures( const QgsFeatureRequ
   return mSource->getFeatures( req );
 }
 
+QgsFeatureSource::FeatureAvailability QgsProcessingFeatureSource::hasFeatures() const
+{
+  if ( !mTransformErrorCallback && !mInvalidGeometryCallback && mInvalidGeometryCheck == QgsFeatureRequest::GeometryNoCheck )
+    return mSource->hasFeatures();
+  else
+    return QgsFeatureSource::FeaturesMaybeAvailable;
+}
+
 QgsFeatureIterator QgsProcessingFeatureSource::getFeatures( const QgsFeatureRequest &request ) const
 {
   QgsFeatureRequest req( request );

src/core/processing/qgsprocessingutils.h

@@ -317,6 +317,8 @@ class CORE_EXPORT QgsProcessingFeatureSource : public QgsFeatureSource
      */
     QgsFeatureIterator getFeatures( const QgsFeatureRequest &request, Flags flags ) const;
 
+    QgsFeatureSource::FeatureAvailability hasFeatures() const override;
+
     QgsFeatureIterator getFeatures( const QgsFeatureRequest &request = QgsFeatureRequest() ) const override;
     QgsCoordinateReferenceSystem sourceCrs() const override;
     QgsFields fields() const override;