fix(PythonQt): Explicitly support immortals introduced in Python >= 3.12

This commit switches to using the `Py_RETURN_*` macros which expand to the
expected constructs. This helps avoid a no-op (and misleading) call to
`Py_INCREF()` when building against Python >= 3.12.

- `Py_RETURN_NOTIMPLEMENTED` was introduced in Python 3.3
  through python/cpython@7d2f9e13424 ("Add Py_RETURN_NOTIMPLEMENTED macro. Fixes #12724.", 2011-08-10)

- `Py_RETURN_TRUE`, `Py_RETURN_FALSE` and `Py_RETURN_NONE` were introduced in
  Python 2.4 through python/cpython@d05235ec49d ("Defined macros Py_RETURN_(TRUE|FALSE|NONE) as helper functions for returning the specified value.  All three Py_INCREF the singleton and then return it.", 2003-10-19)

References:
* https://docs.python.org/3/glossary.html#term-immortal
* https://peps.python.org/pep-0683/

Author: jcfr

src/PythonQt.cpp

@@ -622,8 +622,7 @@ void PythonQtPrivate::createPythonQtClassWrapper(PythonQtClassInfo* info, const
 PyObject* PythonQtPrivate::wrapQObject(QObject* obj)
 {
   if (!obj) {
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   }
   PythonQtInstanceWrapper* wrap = findWrapperAndRemoveUnused(obj);
   if (wrap && wrap->_wrappedPtr) {
@@ -652,8 +651,7 @@ PyObject* PythonQtPrivate::wrapQObject(QObject* obj)
 PyObject* PythonQtPrivate::wrapPtr(void* ptr, const QByteArray& name, bool passOwnership)
 {
   if (!ptr) {
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   }
 
   PythonQtInstanceWrapper* wrap = findWrapperAndRemoveUnused(ptr);

src/PythonQtClassWrapper.cpp

@@ -449,8 +449,7 @@ static PyObject* PythonQtClassWrapper_getDummyInstanceForProperty(PythonQtClassW
   if (info) {
     return (PyObject*)PythonQt::priv()->createNewPythonQtInstanceWrapper(nullptr, info);
   }
-  Py_INCREF(Py_None);
-  return Py_None;
+  Py_RETURN_NONE;
 }
 
 static PyObject *PythonQtClassWrapper_getattro(PyObject *obj, PyObject *name)

src/PythonQtConversion.cpp

@@ -83,22 +83,19 @@ PyObject* PythonQtConv::ConvertQtValueToPython(const PythonQtMethodInfo::Paramet
       return PythonQtPrivate::createEnumValueInstance(info.enumWrapper, *((unsigned int*)data));
     } else {
       // we do not support pointers to enums (who needs them?)
-      Py_INCREF(Py_None);
-      return Py_None;
+      Py_RETURN_NONE;
     }
   }
 
   if (info.typeId == QMetaType::Void) {
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   } else if ((info.pointerCount == 1) && (info.typeId == QMetaType::Char)) {
     // a char ptr will probably be a null terminated string, so we support that:
     char* charPtr = *((char**)data);
     if (charPtr) {
       return PyString_FromString(charPtr);
     } else {
-      Py_INCREF(Py_None);
-      return Py_None;
+      Py_RETURN_NONE;
     }
   } else if ((info.typeId == PythonQtMethodInfo::Unknown || info.typeId >= QMetaType::User) &&
              info.isQList && (info.innerNamePointerCount == 1)) {
@@ -151,15 +148,13 @@ PyObject* PythonQtConv::ConvertQtValueToPython(const PythonQtMethodInfo::Paramet
       }
     }
   }
-  Py_INCREF(Py_None);
-  return Py_None;
+  Py_RETURN_NONE;
 }
 
 PyObject* PythonQtConv::convertQtValueToPythonInternal(int type, const void* data) {
   switch (type) {
   case QMetaType::Void:
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   case QMetaType::Char:
     return PyInt_FromLong(*((char*)data));
   case QMetaType::UChar:
@@ -232,8 +227,7 @@ PyObject* PythonQtConv::convertQtValueToPythonInternal(int type, const void* dat
       }
     }
   }
-  Py_INCREF(Py_None);
-  return Py_None;
+  Py_RETURN_NONE;
  }
 
  void* PythonQtConv::CreateQtReturnValue(const PythonQtMethodInfo::ParameterInfo& info, PythonQtArgumentFrame* frame) {
@@ -1389,8 +1383,7 @@ PyObject* PythonQtConv::QStringListToPyList(const QStringList& list)
 PyObject* PythonQtConv::QVariantToPyObject(const QVariant& v)
 {
   if (!v.isValid()) {
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   }
   PyObject* obj = nullptr;
   if (v.userType() >= QMetaType::User && !PythonQt::priv()->isPythonQtAnyObjectPtrMetaId(v.userType())) {

src/PythonQtImporter.cpp

@@ -191,8 +191,7 @@ PythonQtImporter_find_module(PyObject *obj, PyObject *args)
     Py_INCREF(self);
     return (PyObject *)self;
   } else {
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   }
 }
 
@@ -625,16 +624,14 @@ PythonQtImport::unmarshalCode(const QString& path, const QByteArray& data, time_
   if (size <= 9) {
     PySys_WriteStderr("# %s has bad pyc data\n",
                       QStringToPythonConstCharPointer(path));
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   }
 
   if (getLong((unsigned char *)buf) != PyImport_GetMagicNumber()) {
     if (Py_VerboseFlag)
       PySys_WriteStderr("# %s has bad magic\n",
             QStringToPythonConstCharPointer(path));
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   }
 
   if (mtime != 0) {
@@ -644,8 +641,7 @@ PythonQtImport::unmarshalCode(const QString& path, const QByteArray& data, time_
       if (Py_VerboseFlag)
         PySys_WriteStderr("# %s has bad mtime\n",
         QStringToPythonConstCharPointer(path));
-      Py_INCREF(Py_None);
-      return Py_None;
+      Py_RETURN_NONE;
     }
   }
 

src/PythonQtInstanceWrapper.cpp

@@ -253,8 +253,7 @@ static PyObject *PythonQtInstanceWrapper_richcompare(PythonQtInstanceWrapper* wr
     } else if (validPtrs && code == Py_NE) {
       return PythonQtConv::GetPyBool(!areSamePtrs);
     }
-    Py_INCREF(Py_NotImplemented);
-    return Py_NotImplemented;
+    Py_RETURN_NOTIMPLEMENTED;
   }
 
   QByteArray memberName;
@@ -313,19 +312,16 @@ static PyObject *PythonQtInstanceWrapper_richcompare(PythonQtInstanceWrapper* wr
       // special handling of EQ and NE, if call fails we just return EQ == false / NE == true.
       if (code == Py_EQ) {
         PyErr_Clear();
-        Py_INCREF(Py_False);
-        return Py_False;
+        Py_RETURN_FALSE;
       } else if (code == Py_NE) {
         PyErr_Clear();
-        Py_INCREF(Py_True);
-        return Py_True;
+        Py_RETURN_TRUE;
       }
     }
     return result;
   } else {
     // not implemented, let python try something else!
-    Py_INCREF(Py_NotImplemented);
-    return Py_NotImplemented;
+    Py_RETURN_NOTIMPLEMENTED;
   }
 }
 
@@ -359,8 +355,7 @@ PyObject *PythonQtInstanceWrapper_delete(PythonQtInstanceWrapper * self)
   } else {
     PythonQtInstanceWrapper_deleteObject(self, true);
   }
-  Py_INCREF(Py_None);
-  return Py_None;
+  Py_RETURN_NONE;
 }
 
 
@@ -509,8 +504,7 @@ static PyObject *PythonQtInstanceWrapper_getattro(PyObject *obj,PyObject *name)
         return value;
 
       } else {
-        Py_INCREF(Py_None);
-        return Py_None;
+        Py_RETURN_NONE;
       }
     } else {
       QString error = QString("Trying to read property '") + attributeName + "' from a destroyed " + wrapper->classInfo()->className() + " object";

src/PythonQtProperty.cpp

@@ -179,8 +179,7 @@ static PyObject *PythonQtProperty_get_doc(PythonQtProperty* self, void * /*closu
     return self->data->doc;
   } else {
     //TODO: we could get the doc string from the fget method if no doc string is given...
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
   }
 }
 

src/PythonQtSignal.cpp

@@ -116,8 +116,7 @@ meth_dealloc(PyObject *o)
 static PyObject *
 meth_get__doc__(PythonQtSignalFunctionObject * /*m*/, void * /*closure*/)
 {
-  Py_INCREF(Py_None);
-  return Py_None;
+  Py_RETURN_NONE;
 }
 
 static PyObject *

src/PythonQtStdOut.cpp

@@ -102,8 +102,7 @@ static PyObject *PythonQtStdOutRedirect_flush(PyObject * /*self*/, PyObject * /*
 
 static PyObject *PythonQtStdOutRedirect_isatty(PyObject * /*self*/, PyObject * /*args*/)
 {
-  Py_INCREF(Py_False);
-  return Py_False;
+  Py_RETURN_FALSE;
 }
 
 static PyMethodDef PythonQtStdOutRedirect_methods[] = {