[Scons-users] Dependency missed when the included filename is defined by a preprocessor macro

[Andrew C. Morrow]

I've wondered this at times, and I presume there is a good reason, but for
my own edification I'd like to understand it. Why doesn't SCons, on
platforms that support it, simply invoke the pre-processor with -MG -MDD or
whatever and consume the output? That would be a fully faithful
preprocessor pass, rather than re-implementing the semantics in python.

Thanks,
Andrew


On Tue, Mar 14, 2017 at 11:24 AM, Bill Deegan <bill at baddogconsulting.com>
wrote:

> I beleive you asked this question on stackoverflow and I pointed you at a
> pull request which has much of the preprocessor functionality in it.
> We've not yet merged it, its a work in progress.
>
> Please give that a try.
> -Bill
> SCons Project co-manager
>
> On Tue, Mar 14, 2017 at 8:04 AM, Jean-Baptiste Lab <
> jeanbaptiste.lab at gmail.com> wrote:
>
>> Hi Julien,
>>
>> That would require that SCons implements a fully-fledged preprocessor...
>> It is not the case now and I don't think this is on the roadmap.
>>
>> However, you could maybe wrap the Program builder in a function that
>> would automatically add the HELLO_H value to the dependencies with
>> env.Depends(), using a new env variable like PREPOC_HEADERS?
>>
>> Hope this helps,
>>
>> JB
>>
>>
>> On 2017-03-14 11:16, Julien Pommier wrote:
>>
>> Hi,
>>
>> I’m using a library that #includes a header file whose name is defined by
>> a preprocessor macro. Unfortunately, scons does not seem to add this file
>> to the dependency list of the file that does the #include
>>
>> Here is a short example:
>>
>> I have a hello.c file that is:
>>
>> #include HELLO_H
>> #include <stdio.h>
>> int main() {
>>   printf(MESSAGE);
>>   return 0;
>> }
>>
>> and a hello.h file that is:
>>
>> #define MESSAGE "HELLO\n”
>>
>> My SConstruct is:
>>
>> env=Environment()
>> env.Append(CPPDEFINES={'HELLO_H':'\'"hello.h"\'’})
>> env.Program('hello.c’)
>>
>>
>> The hello program is not rebuilt when I edit the content of ‘hello.h’.
>>
>> Is there a workaround for that ? I know I can add a Depends(‘hello.c’,
>> ‘hello.h’) , but that is not a very convenient solution for me, as I would
>> have to do it in many places.
>>
>> Best regards,
>> Julien
>>
>>
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