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Subject: Re: [Boost-build] IDL and Qt Generator Conflict
From: Vladimir Prus (ghost_at_[hidden])
Date: 2008-11-22 04:43:09

On Friday 14 November 2008 17:52:27 Brad Howes wrote:
> All,
> I'm working on a project that is attempting to use OpenDDS (from the
> ACE/TAO team) along with Nokia's Qt. The build system works great so
> far with just Qt. I created my own simplistic idl.jam tool that
> invokes the two OpenDDS tools to generate the C++ files from an IDL
> spec. For a file Foobar.idl, the first tool generates the following:
> FoobarTypeSupport.idl
> FoobarTypeSupportImpl.cpp
> FoobarTypeSupportImpl.h
> One then runs another tool from ACE/TAO to generate C++ files from the
> (now two) IDL files:
> FoobarTypeSupportC.cpp
> FoobarTypeSupportC.h
> FoobarTypeSupportC.inl
> FoobarTypeSupportS.cpp
> FoobarTypeSupportS.h
> FoobarTypeSupportS.inl
> FoobarC.cpp
> FoobarC.h
> FoobarC.inl
> FoobarS.cpp
> FoobarS.h
> FoobarS.inl
> All of this works just great in Boost Build. The derived files are
> created in the appropriate build variant directory. Here is my
> generator line in the idl.jam file:
> type.register INL : inl : H ;
> generators.register-standard idl.OpenDDS-IDL : IDL :
> CPP(%TypeSupportImpl) CPP(%TypeSupportC) CPP(%TypeSupportS)
> CPP(%C) CPP(%S) INL(%TypeSupportC) INL(%TypeSupportS)
> INL(%C) INL(%S) ;
> What I would like is to add the *.h files as well, using
> H(%TypeSupportImpl), H(%TypeSupportC), etc. But when I do, I get a
> Boost Build error complaining:
> Error: ambiguity found when searching for best transformation
> Trying to produce type 'CPP' from:
> - { Messenger.idl.IDL }
> Generators that succeeded:
> - qt4.moc
> - idl.OpenDDS-IDL
> First generator produced:
> - { qt4%qt4.moc-moc_MessengerC.cpp.CPP { idl%idl.OpenDDS-IDL-
> MessengerC.h.H { Messenger.idl.IDL } } }
> Second generator produced:
> - { idl%idl.OpenDDS-IDL-MessengerTypeSupportC.cpp.CPP
> { Messenger.idl.IDL } }
> .
> .
> .
> I certainly understand the ambiguity, though why does it happen when I
> add "H(%C)" to the generator? Any ideas on how to coexist with another
> generator that handles similar suffixes? For the record, my Qt stuff
> does not use any IDL, so I could conceivably customize my qt4.jam file
> and remove that part.

Hi Brad,
sorry for slow reply -- I've experienced cache miss while trying to answer
this, and might even have to write some code ;-)

The reason this does not happen until you add H(%C) to generator outputs
is that the first transformation:

      - { qt4%qt4.moc-moc_MessengerC.cpp.CPP { idl%idl.OpenDDS-IDL-
         MessengerC.h.H { Messenger.idl.IDL } } }

makes use of the H target. If IDL generator does not produce H target, then
moc generator does not have anything to use.

I do no think this ambiguity can be automatically resolved, in general, so
some explicit override is necessary. I think the best way would be to say:

        - prevent moc generator to use H targets produced by IDL generator

I should be fairly quick to implement, but before I try, anybody sees a better

This mechanism will only allow to resolve the ambiguity -- presently, we don't
have a mechanism to make Boost.Build use *both* transformations. So, if IDL
generator will ever start emitting headers that use Q_OBJECT, we'll in trouble.
But we'll cross the bridge later.

- Volodya

> Finally, just a quick note of thanks to all who work on Boost Build. I
> cannot imagine working on another project without it.
> Thanks,
> Brad

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