[api] Add QgsSipUtils, with method to test if object is owned by Python

QgsSipUtils.isPyOwned will return True if an object is owned
by python, or False if ownership is held by another object
or c++ class.

This gives a way to test in advance if we can safely assign
an object to a method which takes ownership (which always results
in a crash).

python/PyQt6/core/auto_additions/qgssiputils.py

@@ -0,0 +1,5 @@
+# The following has been generated automatically from src/core/qgssiputils.h
+try:
+    QgsSipUtils.isPyOwned = staticmethod(QgsSipUtils.isPyOwned)
+except (NameError, AttributeError):
+    pass

python/PyQt6/core/auto_generated/qgssiputils.sip.in

@@ -0,0 +1,50 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgssiputils.h                                               *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/
+
+
+
+class QgsSipUtils
+{
+%Docstring(signature="appended")
+Contains utilities for working with SIP Python objects.
+
+.. versionadded:: 3.44
+%End
+
+%TypeHeaderCode
+#include "qgssiputils.h"
+%End
+  public:
+
+    static bool isPyOwned( SIP_PYOBJECT /GetWrapper/ );
+%Docstring
+Returns ``True`` if an object is currently owned by Python.
+
+If ``False`` is returned, then the object is currently owned by another
+object (e.g. a c++ class).
+%End
+%MethodCode
+    if ( sipIsOwnedByPython( ( sipSimpleWrapper * )a0Wrapper ) )
+    {
+      sipRes = true;
+    }
+    else
+    {
+      sipRes = false;
+    }
+%End
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgssiputils.h                                               *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/

python/PyQt6/core/core_auto.sip

@@ -170,6 +170,7 @@
 %Include auto_generated/qgsselectioncontext.sip
 %Include auto_generated/qgssimplifymethod.sip
 %Include auto_generated/qgssingleitemmodel.sip
+%Include auto_generated/qgssiputils.sip
 %Include auto_generated/qgssldexportcontext.sip
 %Include auto_generated/qgssnappingconfig.sip
 %Include auto_generated/qgssnappingutils.sip

python/core/auto_additions/qgssiputils.py

@@ -0,0 +1,5 @@
+# The following has been generated automatically from src/core/qgssiputils.h
+try:
+    QgsSipUtils.isPyOwned = staticmethod(QgsSipUtils.isPyOwned)
+except (NameError, AttributeError):
+    pass

python/core/auto_generated/qgssiputils.sip.in

@@ -0,0 +1,50 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgssiputils.h                                               *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/
+
+
+
+class QgsSipUtils
+{
+%Docstring(signature="appended")
+Contains utilities for working with SIP Python objects.
+
+.. versionadded:: 3.44
+%End
+
+%TypeHeaderCode
+#include "qgssiputils.h"
+%End
+  public:
+
+    static bool isPyOwned( SIP_PYOBJECT /GetWrapper/ );
+%Docstring
+Returns ``True`` if an object is currently owned by Python.
+
+If ``False`` is returned, then the object is currently owned by another
+object (e.g. a c++ class).
+%End
+%MethodCode
+    if ( sipIsOwnedByPython( ( sipSimpleWrapper * )a0Wrapper ) )
+    {
+      sipRes = true;
+    }
+    else
+    {
+      sipRes = false;
+    }
+%End
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgssiputils.h                                               *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/

python/core/core_auto.sip

@@ -170,6 +170,7 @@
 %Include auto_generated/qgsselectioncontext.sip
 %Include auto_generated/qgssimplifymethod.sip
 %Include auto_generated/qgssingleitemmodel.sip
+%Include auto_generated/qgssiputils.sip
 %Include auto_generated/qgssldexportcontext.sip
 %Include auto_generated/qgssnappingconfig.sip
 %Include auto_generated/qgssnappingutils.sip

src/core/CMakeLists.txt

@@ -1293,6 +1293,7 @@ set(QGIS_CORE_HDRS
   qgsshapegenerator.h
   qgssimplifymethod.h
   qgssingleitemmodel.h
+  qgssiputils.h
   qgssldexportcontext.h
   qgssnappingconfig.h
   qgssnappingutils.h

src/core/qgssiputils.h

@@ -0,0 +1,56 @@
+/***************************************************************************
+                          qgssiputils.h
+
+                             -------------------
+    begin                : May 2025
+    copyright            : (C) 2025 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSSIPUTILS_H
+#define QGSSIPUTILS_H
+#include "qgis_core.h"
+#include "qgis_sip.h"
+
+/**
+ * \brief Contains utilities for working with SIP Python objects.
+ *
+ * \ingroup core
+ * \since QGIS 3.44
+ */
+class CORE_EXPORT QgsSipUtils
+{
+  public:
+
+#ifdef SIP_RUN
+    /**
+     * Returns TRUE if an object is currently owned by Python.
+     *
+     * If FALSE is returned, then the object is currently owned by another
+     * object (e.g. a c++ class).
+     */
+    static bool isPyOwned( SIP_PYOBJECT SIP_GETWRAPPER );
+    % MethodCode
+    if ( sipIsOwnedByPython( ( sipSimpleWrapper * )a0Wrapper ) )
+    {
+      sipRes = true;
+    }
+    else
+    {
+      sipRes = false;
+    }
+    % End
+#endif
+
+};
+
+#endif //QGSSIPUTILS_H

tests/src/python/CMakeLists.txt

@@ -318,6 +318,7 @@ ADD_PYTHON_TEST(PyQgsSingleBandPseudoColorRenderer test_qgssinglebandpseudocolor
 ADD_PYTHON_TEST(PyQgsSingleSymbolRenderer test_qgssinglesymbolrenderer.py)
 ADD_PYTHON_TEST(PyQgsRasterSingleColorRenderer test_qgsrastersinglecolorrenderer.py)
 ADD_PYTHON_TEST(PyQgsShapefileProvider test_provider_shapefile.py)
+ADD_PYTHON_TEST(PyQgsSipUtils test_qgssiputils.py)
 ADD_PYTHON_TEST(PyQgsSphere test_qgssphere.py)
 ADD_PYTHON_TEST(PyQgsSvgCache test_qgssvgcache.py)
 ADD_PYTHON_TEST(PyQgsSymbolLayerRegistry test_qgssymbollayerregistry.py)

tests/src/python/test_qgssiputils.py

@@ -0,0 +1,43 @@
+"""QGIS Unit tests for QgsSipUtils
+
+.. note:: This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+"""
+
+from qgis.core import (
+    QgsSipUtils,
+    QgsGeometry,
+    QgsSingleSymbolRenderer,
+    QgsPoint,
+    QgsFillSymbol,
+)
+import unittest
+from qgis.testing import QgisTestCase
+
+
+class TestQgsSipUtils(QgisTestCase):
+
+    def test_isPyOwned(self):
+        # not a sip object
+        self.assertTrue(QgsSipUtils.isPyOwned(5))
+
+        p = QgsPoint()
+        self.assertTrue(QgsSipUtils.isPyOwned(p))
+        # assign ownership to other object
+        g = QgsGeometry(p)
+        self.assertTrue(QgsSipUtils.isPyOwned(g))
+        self.assertFalse(QgsSipUtils.isPyOwned(p))
+        self.assertFalse(QgsSipUtils.isPyOwned(g.get()))
+        self.assertTrue(QgsSipUtils.isPyOwned(g.get().clone()))
+
+        renderer = QgsSingleSymbolRenderer(QgsFillSymbol.createSimple({}))
+        self.assertFalse(QgsSipUtils.isPyOwned(renderer.symbol()))
+        renderer2 = renderer.clone()
+        # an object created in c++, never seen before by sip/python
+        self.assertFalse(QgsSipUtils.isPyOwned(renderer2.symbol()))
+
+
+if __name__ == "__main__":
+    unittest.main()