Support the qApp macro correctly, final version incl. debug

For short the new features:
- there is a qApp in QtCore, QtGui and QtWidgets for compatibility,
  and also in __builtins__ for a true macro-like experience.
- if you delete any qApp variable, the Q*Application is reset and you can
  start over.

Long description:

There is a qApp macro in Qt5 which is equivalent to Q*Application.instance() .

Python does not have macros. Both PyQt5 and PySide2 have an
according structure in QtWidgets. In the case of PySide2, the qApp
variable is first initialized to None and later to QApplication().

This does not reflect the original sense of the qApp macro, because
 - it only handles QApplication,
 - it does not handle destruction.

This "macro" should live in QtCore, but both PyQt5 and PySide2 decided
to put this in QtWidgets. As a compromize, I propose to put qApp into
all three modules, and into __builtins__ as well, so wherever you
create an application, you find this "macro" in place.

While changing the code, I stumbled over the template
set_qapp_parent_for_orphan. I tried to make sense out of it and finally
removed it. There were no side effects but bug PYSIDE-85 is gone, now.

With some extra effort, I created a singleton qApp that changes itself.
This way, a true macro was simulated. Note that this was not possible
with a garbage collected variable, and I had to make shiboken aware of this.

As the final optimization, I turned qApp also into a fuse variable:
Delete any qApp variable and Q*Application will finish when there is
no extra reference.

Task-number: PYSIDE-85
Task-number: PYSIDE-571
Change-Id: I7a56b19858f63349c98b95778759a6a6de856938
Reviewed-by: Christian Tismer <tismer@stackless.com>

5 files changed, 283 insertions, 5 deletions

diff --git a/sources/shiboken2/libshiboken/CMakeLists.txt b/sources/shiboken2/libshiboken/CMakeLists.txt
index 3ea7a9f3b..0c954aa07 100644
--- a/sources/shiboken2/libshiboken/CMakeLists.txt
+++ b/sources/shiboken2/libshiboken/CMakeLists.txt
@@ -38,6 +38,7 @@ threadstatesaver.cpp
 typeresolver.cpp
 shibokenbuffer.cpp
 signature.cpp
+qapp_macro.cpp
 )
 
 include_directories(${CMAKE_CURRENT_SOURCE_DIR}
@@ -71,6 +72,7 @@ install(FILES
         shibokenbuffer.h
         sbkpython.h
         signature.h
+        qapp_macro.h
         "${CMAKE_CURRENT_BINARY_DIR}/sbkversion.h"
         DESTINATION include/shiboken2${shiboken2_SUFFIX})
 install(TARGETS libshiboken EXPORT shiboken2
diff --git a/sources/shiboken2/libshiboken/basewrapper.cpp b/sources/shiboken2/libshiboken/basewrapper.cpp
index 3f3bcc7f5..0d8758cee 100644
--- a/sources/shiboken2/libshiboken/basewrapper.cpp
+++ b/sources/shiboken2/libshiboken/basewrapper.cpp
@@ -52,6 +52,7 @@
 #include <algorithm>
 #include "threadstatesaver.h"
 #include "signature.h"
+#include "qapp_macro.h"
 
 namespace {
     void _destroyParentInfo(SbkObject* obj, bool keepReference);
@@ -243,7 +244,9 @@ static void SbkDeallocWrapperCommon(PyObject* pyObj, bool canDelete)
     // be invoked and it trying to delete this object while it is still in
     // progress from the first time around, resulting in a double delete and a
     // crash.
-    PyObject_GC_UnTrack(pyObj);
+    // PYSIDE-571: Some objects do not use GC, so check this!
+    if (PyObject_IS_GC(pyObj))
+        PyObject_GC_UnTrack(pyObj);
 
     // Check that Python is still initialized as sometimes this is called by a static destructor
     // after Python interpeter is shutdown.
@@ -278,6 +281,13 @@ void SbkDeallocWrapper(PyObject* pyObj)
     SbkDeallocWrapperCommon(pyObj, true);
 }
 
+void SbkDeallocQAppWrapper(PyObject* pyObj)
+{
+    SbkDeallocWrapper(pyObj);
+    // PYSIDE-571: make sure to create a singleton deleted qApp.
+    MakeSingletonQAppWrapper(NULL);
+}
+
 void SbkDeallocWrapperWithPrivateDtor(PyObject* self)
 {
     SbkDeallocWrapperCommon(self, false);
@@ -375,9 +385,8 @@ PyObject* SbkObjectTypeTpNew(PyTypeObject* metatype, PyObject* args, PyObject* k
     return reinterpret_cast<PyObject*>(newType);
 }
 
-PyObject* SbkObjectTpNew(PyTypeObject* subtype, PyObject*, PyObject*)
+static PyObject *_setupNew(SbkObject *self, PyTypeObject *subtype)
 {
-    SbkObject* self = PyObject_GC_New(SbkObject, subtype);
     Py_INCREF(reinterpret_cast<PyObject*>(subtype));
     SbkObjectPrivate* d = new SbkObjectPrivate;
 
@@ -394,10 +403,35 @@ PyObject* SbkObjectTpNew(PyTypeObject* subtype, PyObject*, PyObject*)
     self->ob_dict = 0;
     self->weakreflist = 0;
     self->d = d;
-    PyObject_GC_Track(reinterpret_cast<PyObject*>(self));
     return reinterpret_cast<PyObject*>(self);
 }
 
+PyObject* SbkObjectTpNew(PyTypeObject *subtype, PyObject *, PyObject *)
+{
+    SbkObject *self = PyObject_GC_New(SbkObject, subtype);
+    PyObject *res = _setupNew(self, subtype);
+    PyObject_GC_Track(reinterpret_cast<PyObject*>(self));
+    return res;
+}
+
+PyObject* SbkQAppTpNew(PyTypeObject* subtype, PyObject *, PyObject *)
+{
+    // PYSIDE-571:
+    // For qApp, we need to create a singleton Python object.
+    // We cannot track this with the GC, because it is a static variable!
+
+    // Python2 has a weird handling of flags in derived classes that Python3
+    // does not have. Observed with bug_307.py.
+    // But it could theoretically also happen with Python3.
+    // Therefore we enforce that there is no GC flag, ever!
+    if (PyType_HasFeature(subtype, Py_TPFLAGS_HAVE_GC)) {
+        subtype->tp_flags &= ~Py_TPFLAGS_HAVE_GC;
+        subtype->tp_free = PyObject_Del;
+    }
+    SbkObject* self = reinterpret_cast<SbkObject*>(MakeSingletonQAppWrapper(subtype));
+    return self == 0 ? 0 : _setupNew(self, subtype);
+}
+
 
 } //extern "C"
 
@@ -1372,7 +1406,9 @@ void deallocData(SbkObject* self, bool cleanup)
     }
     delete self->d; // PYSIDE-205: always delete d.
     Py_XDECREF(self->ob_dict);
-    Py_TYPE(self)->tp_free(self);
+    // PYSIDE-571: qApp is no longer allocated.
+    if (PyObject_IS_GC((PyObject*)self))
+        Py_TYPE(self)->tp_free(self);
 }
 
 void setTypeUserData(SbkObject* wrapper, void* userData, DeleteUserDataFunc d_func)
diff --git a/sources/shiboken2/libshiboken/basewrapper.h b/sources/shiboken2/libshiboken/basewrapper.h
index a230c1337..bd2d6820f 100644
--- a/sources/shiboken2/libshiboken/basewrapper.h
+++ b/sources/shiboken2/libshiboken/basewrapper.h
@@ -66,6 +66,7 @@ struct LIBSHIBOKEN_API SbkObject
 
 /// Dealloc the python object \p pyObj and the C++ object represented by it.
 LIBSHIBOKEN_API void SbkDeallocWrapper(PyObject* pyObj);
+LIBSHIBOKEN_API void SbkDeallocQAppWrapper(PyObject* pyObj);
 LIBSHIBOKEN_API void SbkDeallocWrapperWithPrivateDtor(PyObject* self);
 
 struct SbkObjectType;
@@ -105,6 +106,8 @@ struct LIBSHIBOKEN_API SbkObjectType
 };
 
 LIBSHIBOKEN_API PyObject* SbkObjectTpNew(PyTypeObject* subtype, PyObject*, PyObject*);
+// the special case of a switchable singleton
+LIBSHIBOKEN_API PyObject* SbkQAppTpNew(PyTypeObject *subtype, PyObject *args, PyObject *kwds);
 
 } // extern "C"
 
diff --git a/sources/shiboken2/libshiboken/qapp_macro.cpp b/sources/shiboken2/libshiboken/qapp_macro.cpp
new file mode 100644
index 000000000..b31e98d06
--- /dev/null
+++ b/sources/shiboken2/libshiboken/qapp_macro.cpp
@@ -0,0 +1,184 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of PySide2.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "basewrapper.h"
+
+extern "C"
+{
+
+#include "qapp_macro.h"
+
+////////////////////////////////////////////////////////////////////////////
+//
+// Support for the qApp macro.
+//
+// qApp is a macro in Qt5. In Python, we simulate that a little by a
+// variable that monitors Q*Application.instance().
+// This variable is also able to destroy the app by deleting qApp.
+//
+static int
+qApp_module_index(PyObject *module)
+{
+    const char *name = PyModule_GetName(module);
+    int ret = 0;
+
+    if (strcmp(name, "PySide2.QtCore") == 0)
+        ret = 1;
+    else if (strcmp(name, "PySide2.QtGui") == 0)
+        ret = 2;
+    else if (strcmp(name, "PySide2.QtWidgets") == 0)
+        ret = 3;
+    return ret;
+}
+
+#define Py_NONE_TYPE Py_TYPE(Py_None)
+
+#if PYTHON_IS_PYTHON3
+#  define BRACE_OPEN {
+#  define BRACE_CLOSE }
+#else
+#  define BRACE_OPEN
+#  define BRACE_CLOSE
+#endif
+
+static SbkObject _Py_ChameleonQAppWrapper_Struct = {
+    BRACE_OPEN
+        _PyObject_EXTRA_INIT
+        1, Py_NONE_TYPE
+    BRACE_CLOSE
+};
+
+static PyObject *qApp_var = NULL;
+static PyObject *qApp_content = (PyObject *)&_Py_ChameleonQAppWrapper_Struct;
+static PyObject *qApp_moduledicts[5] = {0, 0, 0, 0, 0};
+static int qApp_var_ref = 0;
+static int qApp_content_ref = 0;
+
+static int
+reset_qApp_var()
+{
+    PyObject **mod_ptr;
+
+    for (mod_ptr = qApp_moduledicts; *mod_ptr != NULL; mod_ptr++) {
+        // We respect whatever the user may have set.
+        if (PyDict_GetItem(*mod_ptr, qApp_var) == NULL)
+            if (PyDict_SetItem(*mod_ptr, qApp_var, qApp_content) < 0)
+                return -1;
+    }
+    return 0;
+}
+
+
+PyObject *
+MakeSingletonQAppWrapper(PyTypeObject *type)
+{
+    if (type == NULL)
+        type = Py_NONE_TYPE;
+    if (!(type == Py_NONE_TYPE || Py_TYPE(qApp_content) == Py_NONE_TYPE)) {
+        const char *res_name = strrchr(Py_TYPE(qApp_content)->tp_name, '.')+1;
+        const char *type_name = strrchr(type->tp_name, '.')+1;
+        PyErr_Format(PyExc_RuntimeError, "Please destroy the %s singleton before"
+            " creating a new %s instance.", res_name, type_name);
+        return NULL;
+    }
+    if (reset_qApp_var() < 0)
+        return NULL;
+    // always know the max of the refs
+    if (Py_REFCNT(qApp_var) > qApp_var_ref)
+        qApp_var_ref = Py_REFCNT(qApp_var);
+    if (Py_REFCNT(qApp_content) > qApp_content_ref)
+        qApp_content_ref = Py_REFCNT(qApp_content);
+
+    if (Py_TYPE(qApp_content) != Py_NONE_TYPE)
+        Py_REFCNT(qApp_var) = 1; // fuse is armed...
+    if (type == Py_NONE_TYPE) {
+        // Debug mode showed that we need to do more than just remove the
+        // reference. To keep everything in the right order, it is easiest
+        // to do a full shutdown, using QtCore.__moduleShutdown().
+        PyObject *__moduleShutdown = PyDict_GetItemString(qApp_moduledicts[1],
+                                                          "__moduleShutdown");
+        if (__moduleShutdown != NULL) {
+            Py_DECREF(PyObject_CallFunction(__moduleShutdown, (char *)"()"));
+        }
+        // restore the "None-state"
+        Py_TYPE(qApp_content) = Py_NONE_TYPE;
+        Py_REFCNT(qApp_var) = qApp_var_ref;
+        Py_REFCNT(qApp_content) = qApp_content_ref;
+    }
+    else
+        (void)PyObject_INIT(qApp_content, type);
+    Py_INCREF(qApp_content);
+    return qApp_content;
+}
+
+static int
+setup_qApp_var(PyObject *module)
+{
+    int module_index;
+    static int init_done = 0;
+
+    if (!init_done) {
+        qApp_var = Py_BuildValue("s", "qApp");
+        if (qApp_var == NULL)
+            return -1;
+        qApp_moduledicts[0] = PyEval_GetBuiltins();
+        init_done = 1;
+    }
+
+    // Initialize qApp. We insert it into __dict__ for "import *" and also
+    // into __builtins__, to let it appear like a real macro.
+    module_index = qApp_module_index(module);
+    if (module_index) {
+        qApp_moduledicts[module_index] = PyModule_GetDict(module);
+        if (reset_qApp_var() < 0)
+            return -1;
+    }
+    return 0;
+}
+
+void
+NotifyModuleForQApp(PyObject *module)
+{
+    setup_qApp_var(module);
+}
+
+
+} //extern "C"
+
+// end of module
diff --git a/sources/shiboken2/libshiboken/qapp_macro.h b/sources/shiboken2/libshiboken/qapp_macro.h
new file mode 100644
index 000000000..98f0ec629
--- /dev/null
+++ b/sources/shiboken2/libshiboken/qapp_macro.h
@@ -0,0 +1,53 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of PySide2.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QAPP_MACRO_H
+#define QAPP_MACRO_H
+
+#include "sbkpython.h"
+
+extern "C"
+{
+
+LIBSHIBOKEN_API PyObject *MakeSingletonQAppWrapper(PyTypeObject *type);
+LIBSHIBOKEN_API void NotifyModuleForQApp(PyObject *module);
+
+} // extern "C"
+
+#endif // QAPP_MACRO_H