Re-add QgsGeometryEngine::combine taking a list of QgsAbstractGeometries

python/core/geometry/qgsgeometryengine.sip

@@ -73,6 +73,14 @@ class QgsGeometryEngine
 %Docstring
  Calculate the combination of this and ``geom``.
 
+.. versionadded:: 3.0
+ :rtype: QgsAbstractGeometry
+%End
+
+    virtual QgsAbstractGeometry *combine( const QList<QgsAbstractGeometry *> &geomList, QString *errorMsg ) const = 0 /Factory/;
+%Docstring
+ Calculate the combination of this and ``geometries``.
+
 .. versionadded:: 3.0
  :rtype: QgsAbstractGeometry
 %End

src/core/geometry/qgsgeometryengine.h

@@ -91,6 +91,13 @@ class CORE_EXPORT QgsGeometryEngine
      */
     virtual QgsAbstractGeometry *combine( const QgsAbstractGeometry *geom, QString *errorMsg = nullptr ) const = 0 SIP_FACTORY;
 
+    /**
+     * Calculate the combination of this and \a geometries.
+     *
+     * \since QGIS 3.0 \a geom is a pointer
+     */
+    virtual QgsAbstractGeometry *combine( const QList<QgsAbstractGeometry *> &geomList, QString *errorMsg ) const = 0 SIP_FACTORY;
+
     /**
      * Calculate the combination of this and \a geometries.
      *

src/core/geometry/qgsgeos.cpp

@@ -308,6 +308,30 @@ QgsAbstractGeometry *QgsGeos::combine( const QgsAbstractGeometry *geom, QString
   return overlay( geom, OverlayUnion, errorMsg ).release();
 }
 
+QgsAbstractGeometry *QgsGeos::combine( const QList<QgsAbstractGeometry *> &geomList, QString *errorMsg ) const
+{
+  QVector< GEOSGeometry * > geosGeometries;
+  geosGeometries.reserve( geomList.size() );
+  for ( const QgsAbstractGeometry *g : geomList )
+  {
+    if ( !g )
+      continue;
+
+    geosGeometries << asGeos( g, mPrecision ).release();
+  }
+
+  geos::unique_ptr geomUnion;
+  try
+  {
+    geos::unique_ptr geomCollection = createGeosCollection( GEOS_GEOMETRYCOLLECTION, geosGeometries );
+    geomUnion.reset( GEOSUnaryUnion_r( geosinit.ctxt, geomCollection.get() ) );
+  }
+  CATCH_GEOS_WITH_ERRMSG( nullptr )
+
+  std::unique_ptr< QgsAbstractGeometry > result = fromGeos( geomUnion.get() );
+  return result.release();
+}
+
 QgsAbstractGeometry *QgsGeos::combine( const QList<QgsGeometry> &geomList, QString *errorMsg ) const
 {
   QVector< GEOSGeometry * > geosGeometries;

src/core/geometry/qgsgeos.h

@@ -135,6 +135,7 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
     std::unique_ptr< QgsAbstractGeometry > subdivide( int maxNodes, QString *errorMsg = nullptr ) const;
 
     QgsAbstractGeometry *combine( const QgsAbstractGeometry *geom, QString *errorMsg = nullptr ) const override;
+    QgsAbstractGeometry *combine( const QList<QgsAbstractGeometry *> &geomList, QString *errorMsg ) const override;
     QgsAbstractGeometry *combine( const QList< QgsGeometry > &, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *symDifference( const QgsAbstractGeometry *geom, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *buffer( double distance, int segments, QString *errorMsg = nullptr ) const override;