signal: Supply the missing __get__ method

The `__get__` method gets created by `PyType_Ready` when
the slot `tp_descr_get` is set in the signal class.

Change-Id: Id853c59546c0382afeda837f0abfd596b6ca5c7f
Fixes: PYSIDE-68
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

3 files changed, 106 insertions, 2 deletions

diff --git a/sources/pyside2/libpyside/pysidesignal.cpp b/sources/pyside2/libpyside/pysidesignal.cpp
index ff1d6002c..b7941f8d6 100644
--- a/sources/pyside2/libpyside/pysidesignal.cpp
+++ b/sources/pyside2/libpyside/pysidesignal.cpp
@@ -88,6 +88,7 @@ static void signalFree(void *);
 static void signalInstanceFree(void *);
 static PyObject *signalGetItem(PyObject *self, PyObject *key);
 static PyObject *signalToString(PyObject *self);
+static PyObject *signalDescrGet(PyObject *self, PyObject *obj, PyObject *type);
 
 // Signal Instance methods
 static PyObject *signalInstanceConnect(PyObject *, PyObject *, PyObject *);
@@ -137,6 +138,7 @@ static PyTypeObject *PySideMetaSignalTypeF(void)
 
 static PyType_Slot PySideSignalType_slots[] = {
     {Py_mp_subscript,   reinterpret_cast<void *>(signalGetItem)},
+    {Py_tp_descr_get,   reinterpret_cast<void *>(signalDescrGet)},
     {Py_tp_call,        reinterpret_cast<void *>(signalCall)},
     {Py_tp_str,         reinterpret_cast<void *>(signalToString)},
     {Py_tp_init,        reinterpret_cast<void *>(signalTpInit)},
@@ -546,6 +548,19 @@ static PyObject *signalInstanceDisconnect(PyObject *self, PyObject *args)
     return 0;
 }
 
+// PYSIDE-68: Supply the missing __get__ function
+static PyObject *signalDescrGet(PyObject *self, PyObject *obj, PyObject * /*type*/)
+{
+    auto signal = reinterpret_cast<PySideSignal *>(self);
+    // Return the unbound signal if there is nothing to bind it to.
+    if (obj == nullptr || obj == Py_None) {
+        Py_INCREF(self);
+        return self;
+    }
+    Shiboken::AutoDecRef name(Py_BuildValue("s", signal->data->signalName.data()));
+    return reinterpret_cast<PyObject *>(PySide::Signal::initialize(signal, name, obj));
+}
+
 static PyObject *signalCall(PyObject *self, PyObject *args, PyObject *kw)
 {
     auto signal = reinterpret_cast<PySideSignal *>(self);
@@ -759,11 +774,12 @@ static void instanceInitialize(PySideSignalInstance *self, PyObject *name, PySid
 
 PySideSignalInstance *initialize(PySideSignal *self, PyObject *name, PyObject *object)
 {
-    PySideSignalInstance *instance = PyObject_New(PySideSignalInstance, PySideSignalInstanceTypeF());
+    PySideSignalInstance *instance = PyObject_New(PySideSignalInstance,
+                                                  PySideSignalInstanceTypeF());
+    instanceInitialize(instance, name, self, object, 0);
     auto sbkObj = reinterpret_cast<SbkObject *>(object);
     if (!Shiboken::Object::wasCreatedByPython(sbkObj))
         Py_INCREF(object); // PYSIDE-79: this flag was crucial for a wrapper call.
-    instanceInitialize(instance, name, self, object, 0);
     return instance;
 }
 
diff --git a/sources/pyside2/tests/pysidetest/CMakeLists.txt b/sources/pyside2/tests/pysidetest/CMakeLists.txt
index bdd88ea37..97d04426d 100644
--- a/sources/pyside2/tests/pysidetest/CMakeLists.txt
+++ b/sources/pyside2/tests/pysidetest/CMakeLists.txt
@@ -157,6 +157,7 @@ PYSIDE_TEST(properties_test.py)
 PYSIDE_TEST(qapp_like_a_macro_test.py)
 PYSIDE_TEST(qvariant_test.py)
 PYSIDE_TEST(repr_test.py)
+PYSIDE_TEST(signal_tp_descr_get_test.py)
 PYSIDE_TEST(signal_slot_warning.py)
 PYSIDE_TEST(signalandnamespace_test.py)
 PYSIDE_TEST(signalemissionfrompython_test.py)
diff --git a/sources/pyside2/tests/pysidetest/signal_tp_descr_get_test.py b/sources/pyside2/tests/pysidetest/signal_tp_descr_get_test.py
new file mode 100644
index 000000000..61ad8b730
--- /dev/null
+++ b/sources/pyside2/tests/pysidetest/signal_tp_descr_get_test.py
@@ -0,0 +1,87 @@
+#!/usr/bin/python
+
+#############################################################################
+##
+## Copyright (C) 2020 The Qt Company Ltd.
+## Contact: https://www.qt.io/licensing/
+##
+## This file is part of the test suite of Qt for Python.
+##
+## $QT_BEGIN_LICENSE:GPL-EXCEPT$
+## Commercial License Usage
+## Licensees holding valid commercial Qt licenses may use this file in
+## accordance with the commercial license agreement provided with the
+## Software or, alternatively, in accordance with the terms contained in
+## a written agreement between you and The Qt Company. For licensing terms
+## and conditions see https://www.qt.io/terms-conditions. For further
+## information use the contact form at https://www.qt.io/contact-us.
+##
+## GNU General Public License Usage
+## Alternatively, this file may be used under the terms of the GNU
+## General Public License version 3 as published by the Free Software
+## Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+## included in the packaging of this file. Please review the following
+## information to ensure the GNU General Public License requirements will
+## be met: https://www.gnu.org/licenses/gpl-3.0.html.
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+"""
+PYSIDE-68: Test that signals have a `__get__` function after all.
+
+We supply a `tp_descr_get` slot for the signal type.
+That creates the `__get__` method via `PyType_Ready`.
+
+The original test script was converted to a unittest.
+See https://bugreports.qt.io/browse/PYSIDE-68 .
+
+Created:    16 May '12 21:25
+Updated:    17 Sep '20 17:02
+
+This fix was over 8 years late. :)
+"""
+
+from __future__ import print_function
+
+import os
+import sys
+import unittest
+
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+from init_paths import init_test_paths
+init_test_paths(False)
+
+from PySide2 import QtCore
+
+
+def emit_upon_success(signal):
+    def f_(f):
+        def f__(self):
+            result = f(self)
+            s = signal.__get__(self)
+            print(result)
+            return result
+        return f__
+    return f_
+
+
+class Foo(QtCore.QObject):
+    SIG = QtCore.Signal()
+
+    @emit_upon_success(SIG)
+    def do_something(self):
+        print("hooka, it worrrks")
+        return 42
+
+
+class UnderUnderGetUnderUnderTest(unittest.TestCase):
+    def test_tp_descr_get(self):
+        foo = Foo()
+        ret = foo.do_something()
+        self.assertEqual(ret, 42)
+
+
+if __name__ == "__main__":
+    unittest.main()