Take inheritance into account in qgsgeometry_cast

src/core/geometry/qgscurvepolygon.h

@@ -151,7 +151,13 @@ class CORE_EXPORT QgsCurvePolygon: public QgsSurface
      */
     inline const QgsCurvePolygon *cast( const QgsAbstractGeometry *geom ) const
     {
-      if ( geom && QgsWkbTypes::flatType( geom->wkbType() ) == QgsWkbTypes::CurvePolygon )
+      if ( !geom )
+        return nullptr;
+
+      QgsWkbTypes::Type flatType = geom->wkbType();
+      if ( flatType == QgsWkbTypes::CurvePolygon
+           || flatType == QgsWkbTypes::Polygon
+           || flatType == QgsWkbTypes::Triangle )
         return static_cast<const QgsCurvePolygon *>( geom );
       return nullptr;
     }

src/core/geometry/qgsgeometrycollection.h

@@ -146,7 +146,7 @@ class CORE_EXPORT QgsGeometryCollection: public QgsAbstractGeometry
      */
     inline const QgsGeometryCollection *cast( const QgsAbstractGeometry *geom ) const
     {
-      if ( geom && QgsWkbTypes::flatType( geom->wkbType() ) == QgsWkbTypes::GeometryCollection )
+      if ( geom && QgsWkbTypes::isMultiType( geom->wkbType() ) )
         return static_cast<const QgsGeometryCollection *>( geom );
       return nullptr;
     }

src/core/geometry/qgsmulticurve.h

@@ -62,7 +62,12 @@ class CORE_EXPORT QgsMultiCurve: public QgsGeometryCollection
      */
     inline const QgsMultiCurve *cast( const QgsAbstractGeometry *geom )
     {
-      if ( geom && QgsWkbTypes::flatType( geom->wkbType() ) == QgsWkbTypes::MultiCurve )
+      if ( !geom )
+        return nullptr;
+
+      QgsWkbTypes::Type flatType = QgsWkbTypes::flatType( geom->wkbType() );
+      if ( flatType == QgsWkbTypes::MultiCurve
+           ||  flatType == QgsWkbTypes::MultiLineString )
         return static_cast<const QgsMultiCurve *>( geom );
       return nullptr;
     }

src/core/geometry/qgsmultisurface.h

@@ -58,7 +58,13 @@ class CORE_EXPORT QgsMultiSurface: public QgsGeometryCollection
      */
     inline const QgsMultiSurface *cast( const QgsAbstractGeometry *geom )
     {
-      if ( geom && QgsWkbTypes::flatType( geom->wkbType() ) == QgsWkbTypes::MultiSurface )
+      if ( !geom )
+        return nullptr;
+
+      QgsWkbTypes::Type flatType = QgsWkbTypes::flatType( geom->wkbType() );
+
+      if ( flatType == QgsWkbTypes::MultiSurface
+           || flatType == QgsWkbTypes::MultiPolygon )
         return static_cast<const QgsMultiSurface *>( geom );
       return nullptr;
     }

src/core/geometry/qgspolygon.h

@@ -80,7 +80,13 @@ class CORE_EXPORT QgsPolygonV2: public QgsCurvePolygon
      */
     inline const QgsPolygonV2 *cast( const QgsAbstractGeometry *geom ) const
     {
-      if ( geom && QgsWkbTypes::flatType( geom->wkbType() ) == QgsWkbTypes::Polygon )
+      if ( !geom )
+        return nullptr;
+
+      QgsWkbTypes::Type flatType = QgsWkbTypes::flatType( geom->wkbType() );
+
+      if ( flatType == QgsWkbTypes::Polygon
+           || flatType == QgsWkbTypes::Triangle )
         return static_cast<const QgsPolygonV2 *>( geom );
       return nullptr;
     }