feature-select: allow snake_case instead of camelCase for methods

This is the implementation of the first of a series of dynamically
selectable features.

The decision depends of the following setting at the beginning of
a module after PySide2 import:

    from __feature__ import snake_case

For more info, see the Jira issue, section

    The Principle Of Selectable Features In PySide

The crucial problems that are now solved were:

- it is not sufficient to patch a type dict, instead the whole
  `tp_mro` must be walked to rename everything.

- tp_getattro must be changed for every existing type. This
  is done either in shiboken by a changed PyObject_GenericGetAttr
  or PyObject_SenericGetAttr, or in the generated tp_(get|set)attro
  functions.

An example is included in sources/pyside2/doc/tutorial/expenses.

Task-number: PYSIDE-1019
Change-Id: I5f103190be2c884b0b4ad806187f3fef8e6598c9
Reviewed-by: Christian Tismer <tismer@stackless.com>

3 files changed, 117 insertions, 8 deletions

diff --git a/sources/pyside2/tests/QtCore/CMakeLists.txt b/sources/pyside2/tests/QtCore/CMakeLists.txt
index 771e1aeef..0c89f0d03 100644
--- a/sources/pyside2/tests/QtCore/CMakeLists.txt
+++ b/sources/pyside2/tests/QtCore/CMakeLists.txt
@@ -37,12 +37,12 @@ PYSIDE_TEST(deletelater_test.py)
 PYSIDE_TEST(destroysignal_test.py)
 PYSIDE_TEST(duck_punching_test.py)
 PYSIDE_TEST(emoji_string_test.py)
-PYSIDE_TEST(feature_test.py)
 PYSIDE_TEST(hash_test.py)
 PYSIDE_TEST(inherits_test.py)
 PYSIDE_TEST(max_signals.py)
 PYSIDE_TEST(missing_symbols_test.py)
 PYSIDE_TEST(mockclass_test.py)
+PYSIDE_TEST(multiple_feature_test.py)
 PYSIDE_TEST(python_conversion.py)
 PYSIDE_TEST(qabs_test.py)
 PYSIDE_TEST(qabstractitemmodel_test.py)
@@ -128,6 +128,7 @@ PYSIDE_TEST(quuid_test.py)
 PYSIDE_TEST(qversionnumber_test.py)
 PYSIDE_TEST(repr_test.py)
 PYSIDE_TEST(setprop_on_ctor_test.py)
+PYSIDE_TEST(snake_case_feature_test.py)
 PYSIDE_TEST(staticMetaObject_test.py)
 PYSIDE_TEST(static_method_test.py)
 PYSIDE_TEST(thread_signals_test.py)
diff --git a/sources/pyside2/tests/QtCore/feature_test.py b/sources/pyside2/tests/QtCore/multiple_feature_test.py
index cf1e8c3f2..26488326c 100644
--- a/sources/pyside2/tests/QtCore/feature_test.py
+++ b/sources/pyside2/tests/QtCore/multiple_feature_test.py
@@ -37,6 +37,8 @@
 ##
 #############################################################################
 
+from __future__ import print_function, absolute_import
+
 import os
 import sys
 import unittest
@@ -50,12 +52,13 @@ from PySide2.support.__feature__ import _really_all_feature_names
 from textwrap import dedent
 
 """
-feature_test.py
---------------
+multiple_feature_test.py
+------------------------
 
 This tests the selectable features in PySide.
 
-There are no real features implemented. They will be added, later.
+The first feature is `snake_case` instead of `camelCase`.
+There is much more to come.
 """
 
 class FeaturesTest(unittest.TestCase):
@@ -66,9 +69,27 @@ class FeaturesTest(unittest.TestCase):
         """
         global __name__
 
-        for bit in range(8):
+        def tst_bit0(flag, self):
+            if flag == 0:
+                QtCore.QCborArray.isEmpty
+                QtCore.QCborArray.__dict__["isEmpty"]
+                with self.assertRaises(AttributeError):
+                    QtCore.QCborArray.is_empty
+                with self.assertRaises(KeyError):
+                    QtCore.QCborArray.__dict__["is_empty"]
+            else:
+                QtCore.QCborArray.is_empty
+                QtCore.QCborArray.__dict__["is_empty"]
+                with self.assertRaises(AttributeError):
+                    QtCore.QCborArray.isEmpty
+                with self.assertRaises(KeyError):
+                    QtCore.QCborArray.__dict__["isEmpty"]
+
+        edict = {}
+        for bit in range(1, 8):
             # We are cheating here, since the functions are in the globals.
-            exec(dedent("""
+
+            eval(compile(dedent("""
 
         def tst_bit{0}(flag, self):
             if flag == 0:
@@ -80,7 +101,8 @@ class FeaturesTest(unittest.TestCase):
                 QtCore.QCborArray.fake_feature_{1:02x}
                 QtCore.QCborArray.__dict__["fake_feature_{1:02x}"]
 
-                        """.format(bit, 1 << bit)), globals(), globals())
+                        """).format(bit, 1 << bit), "<string>", "exec"), globals(), edict)
+        globals().update(edict)
         feature_list = _really_all_feature_names
         func_list = [tst_bit0, tst_bit1, tst_bit2, tst_bit3,
                      tst_bit4, tst_bit5, tst_bit6, tst_bit7]
@@ -95,7 +117,7 @@ class FeaturesTest(unittest.TestCase):
                     feature = feature_list[bit]
                     text = "from __feature__ import {}".format(feature)
                     print(text)
-                    exec(text)
+                    eval(compile(text, "<string>", "exec"), globals(), edict)
             for bit in range(8):
                 value = idx & 1 << bit
                 func_list[bit](value, self=self)
diff --git a/sources/pyside2/tests/QtCore/snake_case_feature_test.py b/sources/pyside2/tests/QtCore/snake_case_feature_test.py
new file mode 100644
index 000000000..b7f23396e
--- /dev/null
+++ b/sources/pyside2/tests/QtCore/snake_case_feature_test.py
@@ -0,0 +1,86 @@
+#############################################################################
+##
+## Copyright (C) 2020 The Qt Company Ltd.
+## Contact: https://www.qt.io/licensing/
+##
+## This file is part of Qt for Python.
+##
+## $QT_BEGIN_LICENSE:LGPL$
+## 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 Lesser General Public License Usage
+## Alternatively, this file may be used under the terms of the GNU Lesser
+## General Public License version 3 as published by the Free Software
+## Foundation and appearing in the file LICENSE.LGPL3 included in the
+## packaging of this file. Please review the following information to
+## ensure the GNU Lesser General Public License version 3 requirements
+## will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+##
+## GNU General Public License Usage
+## Alternatively, this file may be used under the terms of the GNU
+## General Public License version 2.0 or (at your option) the GNU General
+## Public license version 3 or any later version approved by the KDE Free
+## Qt Foundation. The licenses are as published by the Free Software
+## Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+## 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-2.0.html and
+## https://www.gnu.org/licenses/gpl-3.0.html.
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+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 QtWidgets
+
+"""
+snake_case_feature_test.py
+--------------------------
+
+Test the snake_case feature.
+
+This works now. More tests needed!
+"""
+
+class RenamingTest(unittest.TestCase):
+    def setUp(self):
+        qApp or QtWidgets.QApplication()
+
+    def tearDown(self):
+        qApp.shutdown()
+
+    def testRenamedFunctions(self):
+
+        class Window(QtWidgets.QWidget):
+            def __init__(self):
+                super(Window, self).__init__()
+
+        window = Window()
+        window.setWindowTitle('camelCase')
+
+        # and now the same with snake_case enabled
+        from __feature__ import snake_case
+
+        class Window(QtWidgets.QWidget):
+            def __init__(self):
+                super(Window, self).__init__()
+
+        window = Window()
+        window.set_window_title('snake_case')
+
+if __name__ == '__main__':
+    unittest.main()