Add CTK pragma macros and fix "PythonQtInstanceWrapper.h" -Wold-style-cast warnings

[jcfr]

The macros were adapted from ITK and allow to avoid warnings like the following:

/path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtInstanceWrapper.h: In member function ‘PythonQtClassInfo* PythonQtInstanceWrapperStruct::classInfo()’:
/path/to/Slicer-build/python-install/include/python2.7/object.h:115:49: warning: use of old-style cast [-Wold-style-cast]
 #define Py_TYPE(ob)             (((PyObject*)(ob))->ob_type)
                                                 ^
/path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtInstanceWrapper.h:68:37: note: in expansion of macro ‘Py_TYPE’
   {  return ((PythonQtClassWrapper*)Py_TYPE(this))->_classInfo; }
                                     ^

[jcfr]

Since the can be of general use in the remaining of CTK (and also user code) I added them to ctkMacro.h.

• We could also introduce a header named "ctkPythonQt.h" that would systematically be included (instead of PythonQt.h), this header would then be used everywhere in CTK/Slicer/...

• or we could work in fixing PythonQt ...

[jcfr]

for reference, here is the email sent to the pythonqt discussion forum (not yet visible):

---

Hi Florian,

Would you accept a patch like the following to systematically ignore old-style cast warnings ?

That would be very helpful and avoid user code to maintain their own guard headers.

diff --git a/src/PythonQtPythonInclude.h b/src/PythonQtPythonInclude.h
index 00f0b07..bd20c76 100644
--- a/src/PythonQtPythonInclude.h
+++ b/src/PythonQtPythonInclude.h
@@ -44,6 +44,15 @@
 #define PYTHONQT_RESTORE_KEYWORDS
 #endif
 
+// Ignore "old-style-cast" warnings  associated with use of macro like Py_TYPE
+// provided by pythonX.Y/object.h
+#if defined( __GNUC__ )
+#if ( __GNUC__ == 4 ) && ( __GNUC_MINOR__ == 9 ) || ( __GNUC__ >= 7 )
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wold-style-cast"
+#endif
+#endif
+
 // If PYTHONQT_USE_RELEASE_PYTHON_FALLBACK is enabled, try to link
 // release Python DLL if it is available by undefining _DEBUG while
 // including Python.h
@@ -59,6 +68,12 @@
 #include <Python.h>
 #endif
 
+#if defined( __GNUC__ )
+#if ( __GNUC__ == 4 ) && ( __GNUC_MINOR__ == 9 ) || ( __GNUC__ >= 7 )
+#pragma GCC diagnostic pop
+#endif
+#endif
+

Example of warnings:

/path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtInstanceWrapper.h: In member function ‘PythonQtClassInfo* PythonQtInstanceWrapperStruct::classInfo()’:
/path/to/Slicer-build/python-install/include/python2.7/object.h:115:49: warning: use of old-style cast [-Wold-style-cast]
 #define Py_TYPE(ob)             (((PyObject*)(ob))->ob_type)
                                                 ^
/path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtInstanceWrapper.h:68:37: note: in expansion of macro ‘Py_TYPE’
   {  return ((PythonQtClassWrapper*)Py_TYPE(this))->_classInfo; }
                                     ^
/path/to/Slicer-build/python-install/include/python2.7/object.h:115:60: warning: use of old-style cast [-Wold-style-cast]
 #define Py_TYPE(ob)             (((PyObject*)(ob))->ob_type)
                                                            ^
/path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtInstanceWrapper.h:68:37: note: in expansion of macro ‘Py_TYPE’
   {  return ((PythonQtClassWrapper*)Py_TYPE(this))->_classInfo; }
                                     ^
/path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtInstanceWrapper.h: In member function ‘PythonQtDynamicClassInfo* PythonQtInstanceWrapperStruct::dynamicClassInfo()’:
/path/to/Slicer-build/python-install/include/python2.7/object.h:115:49: warning: use of old-style cast [-Wold-style-cast]
 #define Py_TYPE(ob)             (((PyObject*)(ob))->ob_type)
                                                 ^

[jcfr]

It turns out that (1) the patch was incorrect and (2) updating PythonQtPythonInclude.h by pushing/poping context is not working.

Instead the following should be done:

diff --git a/src/PythonQt.h b/src/PythonQt.h
index fd2e28e..643d984 100644
--- a/src/PythonQt.h
+++ b/src/PythonQt.h
@@ -42,6 +42,15 @@
 */
 //----------------------------------------------------------------------------------
 
+// Ignore "old-style-cast" warnings  associated with use of macro like Py_TYPE
+// provided by pythonX.Y/object.h
+#if defined( __GNUC__ )
+#if ( __GNUC__ > 4 ) || (( __GNUC__ >= 4 ) && ( __GNUC_MINOR__ >= 6 ))
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wold-style-cast"
+#endif
+#endif
+
 #include "PythonQtPythonInclude.h"
 #include "PythonQtUtils.h"
 #include "PythonQtSystem.h"
@@ -51,6 +60,13 @@
 #include "PythonQtObjectPtr.h"
 #include "PythonQtStdIn.h"
 #include "PythonQtThreadSupport.h"
+
+#if defined( __GNUC__ )
+#if ( __GNUC__ > 4 ) || (( __GNUC__ >= 4 ) && ( __GNUC_MINOR__ >= 6 ))
+#pragma GCC diagnostic pop
+#endif
+#endif
+
 #include <QObject>
 #include <QVariant>
 #include <QList>