[Cython] Fwd: Question about how best require compiler options for C sources

[Nathaniel Smith]

Can you give a tiny concrete example? My questions are basic enough that I
feel like I'm missing something fundamental :-)

My first question is why you even need this, since AFAIK there are no cases
where it is correct to have a cython module dllexporting symbols that
appear in header files. This is what cimport is for, right?

My second question is why you would want to do this via the command line,
when compiling the dll means that you are compiling some cython-generated
.c, which means that you can put the #define directly in the source code,
no?

-n
On Apr 8, 2016 5:35 AM, "Erik Bray" <erik.m.bray at gmail.com> wrote:

> Hi all,
>
> I'd like to call attention to an issue I've been looking into for the
> past couple days:
>
> https://github.com/cython/cython/pull/360
>
> To summarize the discussion, when building DLLs for Windows, functions
> that should be exported by that DLL must be marked
> __declspec(dllexport) in their declaration.  However, when using the
> same header file in a project that links to that DLL the same function
> must be declared __declspec(dllimport).
>
> It's common practice to have a macro for this, whose value is
> controlled by whether or not a macro (often called something like
> "DLL_EXPORT").  When compiling the DLL we would define -DDLL_EXPORT to
> output __declspec(dllexport).  Otherwise it outputs
> __declspec(dllimport).
>
> Cython currently handles this with such a macro called DL_IMPORT which
> comes from Python. However, this macro was deprecated some time ago,
> and is removed in current Python 3 versions.  So Cython must replace
> it with its own.
>
> I'm working on a patch for this--to reduce confusion the macro is
> named specifically for the Cython module it's associated with.  For
> example, for a Cython module named "foo.bar" there are two macros
> DLL_EXPORT__foo__bar and EXPORT__foo__bar.  If the latter is defined
> then the former outputs dllexport, otherwise it outputs dllimport.
> I've attached the patch in progress.
>
> I'm open to comment on this, but where I'm stuck now is that in order
> for the "foo.bar" module to be compiled correctly it needs
> EXPORT__foo__bar to be defined at compile time.  And it's not clear to
> me what the best way is for the Cython compiler to pass down options
> that are passed to the C/C++ compiler.  In general the best way would
> be to attach this to the define_macros attribute of the associated
> distutils/setuptools Extension object and let the distutils compiler
> class generate the right compiler options.  But it's not clear to me
> from Cython's internals where the best place to do that would be.
>
> Thanks,
> Erik
>
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