[api] Raises ValueError and TypeError exceptions when QgsGeometry.asPoint()

is called on non-single-point geometries

Previously we would just return QgsPointXY(0,0) when geometries of invalid
type were used, but this is dangerous and we are safer to explicitly
raise errors preventing use of asPoint() with incompatible geometry types.

Author: nyalldawson

python/core/auto_generated/geometry/qgsgeometry.sip.in

@@ -1413,10 +1413,33 @@ Try to convert the geometry to the requested type
 %End
 
 
-    QgsPointXY asPoint() const;
+
+    SIP_PYOBJECT asPoint() const /TypeHint="QgsPointXY"/;
 %Docstring
-Returns contents of the geometry as a point
-if wkbType is WKBPoint, otherwise returns [0,0]
+Returns the contents of the geometry as a 2-dimensional point.
+
+Any z or m values present in the geometry will be discarded.
+
+This method works only with single-point geometry types. If the geometry
+is not a single-point type, a TypeError will be raised. If the geometry
+is null, a ValueError will be raised.
+%End
+%MethodCode
+    const QgsWkbTypes::Type type = sipCpp->wkbType();
+    if ( sipCpp->isNull() )
+    {
+      PyErr_SetString( PyExc_ValueError, QStringLiteral( "Null geometry cannot be converted to a point." ).toUtf8().constData() );
+      sipIsErr = 1;
+    }
+    else if ( QgsWkbTypes::flatType( type ) != QgsWkbTypes::Point )
+    {
+      PyErr_SetString( PyExc_TypeError, QStringLiteral( "%1 geometry cannot be converted to a point. Only Point types are permitted." ).arg( QgsWkbTypes::displayString( type ) ).toUtf8().constData() );
+      sipIsErr = 1;
+    }
+    else
+    {
+      sipRes = sipConvertFromNewType( new QgsPointXY( sipCpp->asPoint() ), sipType_QgsPointXY, Py_None );
+    }
 %End
 
     QgsPolylineXY asPolyline() const;

src/core/geometry/qgsgeometry.h

@@ -1413,11 +1413,46 @@ class CORE_EXPORT QgsGeometry
 
     /* Accessor functions for getting geometry data */
 
+#ifndef SIP_RUN
+
     /**
-     * Returns contents of the geometry as a point
-     * if wkbType is WKBPoint, otherwise returns [0,0]
+     * Returns the contents of the geometry as a 2-dimensional point.
+     *
+     * Any z or m values present in the geometry will be discarded.
+     *
+     * \warning If the geometry is not a single-point type, a QgsPoint( 0, 0 ) will be returned.
      */
     QgsPointXY asPoint() const;
+#else
+
+    /**
+     * Returns the contents of the geometry as a 2-dimensional point.
+     *
+     * Any z or m values present in the geometry will be discarded.
+     *
+     * This method works only with single-point geometry types. If the geometry
+     * is not a single-point type, a TypeError will be raised. If the geometry
+     * is null, a ValueError will be raised.
+     */
+    SIP_PYOBJECT asPoint() const SIP_TYPEHINT( QgsPointXY );
+    % MethodCode
+    const QgsWkbTypes::Type type = sipCpp->wkbType();
+    if ( sipCpp->isNull() )
+    {
+      PyErr_SetString( PyExc_ValueError, QStringLiteral( "Null geometry cannot be converted to a point." ).toUtf8().constData() );
+      sipIsErr = 1;
+    }
+    else if ( QgsWkbTypes::flatType( type ) != QgsWkbTypes::Point )
+    {
+      PyErr_SetString( PyExc_TypeError, QStringLiteral( "%1 geometry cannot be converted to a point. Only Point types are permitted." ).arg( QgsWkbTypes::displayString( type ) ).toUtf8().constData() );
+      sipIsErr = 1;
+    }
+    else
+    {
+      sipRes = sipConvertFromNewType( new QgsPointXY( sipCpp->asPoint() ), sipType_QgsPointXY, Py_None );
+    }
+    % End
+#endif
 
     /**
      * Returns contents of the geometry as a polyline

tests/src/python/test_qgsgeometry.py

@@ -546,6 +546,23 @@ def testCurvePolygonPythonAdditions(self):
         with self.assertRaises(IndexError):
             g.removeInteriorRing(0)
 
+    def testPointXY(self):
+        """
+        Test the QgsPointXY conversion methods
+        """
+        self.assertEqual(QgsGeometry.fromWkt('Point(11 13)').asPoint(), QgsPointXY(11, 13))
+        self.assertEqual(QgsGeometry.fromWkt('PointZ(11 13 14)').asPoint(), QgsPointXY(11, 13))
+        self.assertEqual(QgsGeometry.fromWkt('PointM(11 13 14)').asPoint(), QgsPointXY(11, 13))
+        self.assertEqual(QgsGeometry.fromWkt('PointZM(11 13 14 15)').asPoint(), QgsPointXY(11, 13))
+        with self.assertRaises(TypeError):
+            QgsGeometry.fromWkt('MultiPoint(11 13,14 15)').asPoint()
+        with self.assertRaises(TypeError):
+            QgsGeometry.fromWkt('LineString(11 13,14 15)').asPoint()
+        with self.assertRaises(TypeError):
+            QgsGeometry.fromWkt('Polygon((11 13,14 15, 14 13, 11 13))').asPoint()
+        with self.assertRaises(ValueError):
+            QgsGeometry().asPoint()
+
     def testReferenceGeometry(self):
         """ Test parsing a whole range of valid reference wkt formats and variants, and checking
         expected values such as length, area, centroids, bounding boxes, etc of the resultant geometry.