Signature: fix the __doc__ attribute of classes

The signature module had been changed to no longer default
the __doc__ attribute of classes to the __init__ signature.
This has the side effect of crashing "help(QtCore)".

Fixed by correct defaults in C++ (AttributeError) and by
setting a "None" default in the Python handler.

The make_helptest function defaults again correctly to the signature:

    >>> errorhandler.make_helptext(QtWidgets.QApplication)
    'QApplication(self) -> None\nQApplication(self, arg__1: Sequence[str]) -> None'

Change-Id: I140f2b940f98eb126541b18b0feb312c7c4e9728
Fixes: PYSIDE-1727
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
(cherry picked from commit 8901719fd74ce8d8909608365e68f7354adaa254)
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

3 files changed, 13 insertions, 5 deletions

diff --git a/sources/pyside6/tests/QtCore/errormessages_with_features_test.py b/sources/pyside6/tests/QtCore/errormessages_with_features_test.py
index 72452a588..4a515c800 100644
--- a/sources/pyside6/tests/QtCore/errormessages_with_features_test.py
+++ b/sources/pyside6/tests/QtCore/errormessages_with_features_test.py
@@ -46,9 +46,12 @@ sys.path.append(os.fspath(Path(__file__).resolve().parents[1]))
 from init_paths import init_test_paths
 init_test_paths(False)
 
+from PySide6 import QtCore
 from PySide6.QtWidgets import QApplication, QLabel
 from PySide6.support import __feature__
 
+import inspect
+
 """
 errormessages_with_features_test.py
 -----------------------------------
@@ -120,6 +123,13 @@ class ErrormessagesWithFeatures(unittest.TestCase):
             qApp.quit_on_last_window_closed = object
         self.assertTrue(self.probe_miss in cm.exception.args[0])
 
+    def testDocIsWorking(self):
+        """
+        make sure that it does not crash when touched
+        """
+        inspect.getdoc(QApplication)
+        inspect.getdoc(QtCore)
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/sources/shiboken6/libshiboken/signature/signature_extend.cpp b/sources/shiboken6/libshiboken/signature/signature_extend.cpp
index 4b67d778f..c7aedef08 100644
--- a/sources/shiboken6/libshiboken/signature/signature_extend.cpp
+++ b/sources/shiboken6/libshiboken/signature/signature_extend.cpp
@@ -173,10 +173,8 @@ static PyObject *handle_doc(PyObject *ob, PyObject *old_descr)
                         pyside_globals->make_helptext_func,
                         "(O)", ob);
     handle_doc_in_progress--;
-    if (res == nullptr) {
-        PyErr_Print();
-        Py_FatalError("handle_doc did not receive a result");
-    }
+    if (res == nullptr)
+        PyErr_Format(PyExc_AttributeError, "%R object has no `__doc__` attribute", ob);
     return res;
 }
 
diff --git a/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/errorhandler.py b/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/errorhandler.py
index 4c436eafd..6cab8746f 100644
--- a/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/errorhandler.py
+++ b/sources/shiboken6/shibokenmodule/files.dir/shibokensupport/signature/errorhandler.py
@@ -156,7 +156,7 @@ def check_string_type(s):
 
 
 def make_helptext(func):
-    existing_doc = func.__doc__
+    existing_doc = func.__doc__ if hasattr(func, "__doc__") else None
     sigs = get_signature(func)
     if not sigs:
         return existing_doc