cppgenerator: rework keyword handling regarding unknown.. Fixed!

The new keyword algorithm did fail again on Windows.
But this time it was a refcounting error that was only visible
in a debug build.

On Windows, it appeared as a negative refcount assertion.
On macOS in debug mode, it was a segfault instead.

The problem was `PyErr_Fetch()`, a function that uses borrowed
references, only. Forgot to respect that, sorry :-(

Task-number: PYSIDE-1305
Change-Id: I164668db8143729fa2fab0be1f61757690e13138
Pick-to: 5.15
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 4 insertions, 7 deletions

diff --git a/sources/shiboken6/libshiboken/signature/signature.cpp b/sources/shiboken6/libshiboken/signature/signature.cpp
index 7f57aa8a3..130aeb778 100644
--- a/sources/shiboken6/libshiboken/signature/signature.cpp
+++ b/sources/shiboken6/libshiboken/signature/signature.cpp
@@ -521,13 +521,11 @@ void SetError_Argument(PyObject *args, const char *func_name, PyObject *info)
     init_module_2();
 
     // PYSIDE-1305: Handle errors set by fillQtProperties.
-    PyObject *err_val{};
     if (PyErr_Occurred()) {
-        PyObject *e, *t;
-        PyErr_Fetch(&e, &err_val, &t);
-        info = err_val;
-        Py_XDECREF(&e);
-        Py_XDECREF(&t);
+        PyObject *e, *v, *t;
+        // Note: These references are all borrowed.
+        PyErr_Fetch(&e, &v, &t);
+        info = v;
     }
     // PYSIDE-1019: Modify the function name expression according to feature.
     AutoDecRef new_func_name(adjustFuncName(func_name));
@@ -548,7 +546,6 @@ void SetError_Argument(PyObject *args, const char *func_name, PyObject *info)
         PyErr_Print();
         Py_FatalError("unexpected failure in seterror_argument");
     }
-    Py_XDECREF(err_val);
     PyErr_SetObject(err, msg);
 }