Re: [Boost-build] implicit-dependency problem

From: Daniel Einspanjer (deinspanjer_at_[hidden])
Date: 2006-02-13 10:41:45

"Vladimir Prus" <ghost_at_[hidden]> wrote in message 
news:200602131407.27571.ghost_at_cs.msu.su...
>> > 1. The '<implicit-dependency>' won't automatically build 'msg'. It just 
>> > means
>> > 'I think there's header in 'msg' that this target depends on'. This is 
>> > by
>> > design (though if you think that's wrong design, I'm open to 
>> > arguments).
>>
>> I would expect msg to be built by a bjam test if the mc file changed 
>> since
>> the header is a dependant of that file.  Would you agree?
>
> No, not quite. The header should be rebuilt, because it's dependendant of
> ".mc" file and it's included by 'log.cpp' and 'log.cpp' is being built.
>
> But you did not request build of the 'msg' target, so it's not build. If 
> you
> want 'msg' to be always built when you build 'test', you add the
> <dependency>msg. Otherwise, only required target, in this case the 
> generated
> header, will be built.

I understand the distinction you are making here.  I agree that, in this 
case, only the header should be built, not the dll.

>> If msg were a static lib instead of a shared lib, building an exe that
>> depended on msg should cause msg to be rebuilt if msg.cpp.
>
> Seems like you've omitted something in that sentence. I assume "if msg.cpp 
> is
> out-of-date". Yes, if "exe" target depends on "msg", then "msg" will be
> rebuild if msg.mc is modified.
>
>> In this case
>> however, I would agree that <implicit-dependency> alone shouldn't cause
>> that behavior.  In that case, I think the exe target should have both
>> <implicit-dependency> and <dependency> to indicate the two subtly 
>> different
>> dependencies on the msg target.
>
> If your exe uses the library at link time, then add the library to the
> sources, and use extra <implicit-dependency> as a hint about generated
> headers.
>
> If you exe uses a shared library as plugin, it might be desirable to build 
> the
> library whenever the exe is built, without linking to it. In that case
> <dependency> + <implicit-dependency> is best.

This all makes sense to me.

> Ok, great. I've just comitted the *right* fix for this problem:
>
> 
> http://sourceforge.net/mailarchive/forum.php?thread_id=9710540&forum_id=9097
> 
> http://sourceforge.net/mailarchive/forum.php?thread_id=9710539&forum_id=9097
>
> it differs only by the location where new code is added, and extra 
> comments
> and tests.
>
> Can you undo the patch I've sent previously, update to current CVS and see 
> if
> everything's OK.
>
Done and my targets continue to build in the fashion you indicated above.

Thanks for helping me with this!

Daniel