signature: Add support for classmethods

Two tests were adapted, because now the missing signature
error message:

    TypeError: xxx.__dict__['yyy'].fset(<class 'object'>) is wrong (missing signature)

does not apply, and we get the usual message:

    TypeError: xxx.__dict__['yyy'].fset" called with wrong argument types:

this comes from the fact that we are not getting the string
representation of the signature, but the data type itself.

Change-Id: Ib9c8b7f863063b384c41dea32e2b4b01f0695f82
Fixes: PYSIDE-1955
Pick-to: 6.5 6.2
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
(cherry picked from commit 94869cf1cacb1a5c2d722f49feb8e8af895144bc)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 7 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 8cb38882a..97c4f942e 100644
--- a/sources/pyside6/tests/QtCore/errormessages_with_features_test.py
+++ b/sources/pyside6/tests/QtCore/errormessages_with_features_test.py
@@ -34,7 +34,6 @@ This test is in its own file because combining it with
 @unittest.skipIf(is_pypy, "__feature__ cannot yet be used with PyPy")
 class ErrormessagesWithFeatures(unittest.TestCase):
     probe = "called with wrong argument types"
-    probe_miss = "missing signature"
 
     def setUp(self):
         qApp or QApplication()
@@ -76,20 +75,20 @@ class ErrormessagesWithFeatures(unittest.TestCase):
         with self.assertRaises(TypeError) as cm:
             QApplication.quitOnLastWindowClosed = object
         print("\n\n" + cm.exception.args[0])
-        self.assertTrue(self.probe_miss in cm.exception.args[0])
+        self.assertTrue(self.probe in cm.exception.args[0])
         with self.assertRaises(TypeError) as cm:
             qApp.quitOnLastWindowClosed = object
-        self.assertTrue(self.probe_miss in cm.exception.args[0])
+        self.assertTrue(self.probe in cm.exception.args[0])
 
     def testCorrectErrorMessagesClassSnakeProp(self):
         from __feature__ import snake_case, true_property
         with self.assertRaises(TypeError) as cm:
             QApplication.quit_on_last_window_closed = object
         print("\n\n" + cm.exception.args[0])
-        self.assertTrue(self.probe_miss in cm.exception.args[0])
+        self.assertTrue(self.probe in cm.exception.args[0])
         with self.assertRaises(TypeError) as cm:
             qApp.quit_on_last_window_closed = object
-        self.assertTrue(self.probe_miss in cm.exception.args[0])
+        self.assertTrue(self.probe in cm.exception.args[0])
 
     def testDocIsWorking(self):
         """
diff --git a/sources/shiboken6/libshiboken/signature/signature.cpp b/sources/shiboken6/libshiboken/signature/signature.cpp
index 814d0ceab..04eb974f0 100644
--- a/sources/shiboken6/libshiboken/signature/signature.cpp
+++ b/sources/shiboken6/libshiboken/signature/signature.cpp
@@ -248,6 +248,9 @@ PyObject *get_signature_intern(PyObject *ob, PyObject *modifier)
         return pyside_tp_get___signature__(ob, modifier);
     if (Py_TYPE(ob) == &PyWrapperDescr_Type)
         return pyside_wd_get___signature__(ob, modifier);
+    // For classmethods we use the simple wrapper description implementation.
+    if (Py_TYPE(ob) == &PyClassMethodDescr_Type)
+        return pyside_wd_get___signature__(ob, modifier);
     return nullptr;
 }