[Cython] Windows Debug build improvement

[Robert Bradshaw]

On Thu, Jul 18, 2013 at 6:24 AM, Wolfgang <tds333 at gmail.com> wrote:
> Hi,
>
> I tried to submit a improvement for the Windows build but the tracker is not
> accessible without a login.

This is to prevent spam.

> On Windows if someone does a Debug build of an extension the flag _DEBUG is
> set and so the Python Interpreter sets Py_DEBUG and for all extension modules
> "_d" is appended to load the debug version of a module.
> This is not really practical because then all modules and the Python
> Interpreter must be build in Debug mode. For some modules this is even not
> possible for Windows. :-(
>
> To do a debug build for a Cython generated extension with a normal Python
> Interpreter (none Debug) I have to patch the pyconfig.h file and undef _DEBUG
> or I must patch the generated c file from Cython to undef _DEBUG before
> pyconfig.h or Python.h is included. (and enable it afterwards)
>
> Is it possible to add a flag to Cython to generate code that does this ?
>
> Something like described in Boost.Python:
> http://hepunx.rl.ac.uk/BFROOT/dist/releases/26.0.0/boost/libs/python/doc/building.html
>
> It is enough to have a new Preprocessor Flag, if set, then surround the
> Python.h inclusion with a disabled _DEBUG.
>
> My workarround is to disable it before pyconfig.h (Python.h) include:
>
> #ifdef _DEBUG
> #undef _DEBUG
> #define _RESTORE
> #endif
>
> and enable it afterwards
>
> #ifdef _RESTORE
> #define _DEBUG
> #undef _RESTORE
> #endif

Seems like a fairly global change. At the very least it should be
guarded with an #if [windows/msvc/?], and _RESTORE probably named
__PYX_RESTORE_DEBUG or something less likely to clash. But it'd be
really helpful for someone who uses and knows windows well to comment
on the possible implications of this, as I don't even have a way to
try it out.