Re: [Caml-list] findlib help: how to specify dependencies against non-findlib packages ?

[Gerd Stolpmann <info@gerd-stolpmann.de>]

Am Montag, den 02.10.2006, 15:30 +0200 schrieb Guillaume Rousse:
> Gerd Stolpmann wrote:
> > Am Montag, den 02.10.2006, 11:24 +0200 schrieb Guillaume Rousse:
> >> I'm trying to add findlibsupport for camlimages.
> >>
> >> It has a dependency on graphics, which is easily handled by adding a
> >> require variable in META file, as graphics provides findlib support.
> >>
> >> However, camlimages can also get compiled with either lablgtk or
> >> lablgtk2 support (not both of them, as they have conflicting symbols),
> >> but none of those packages have findlib support. It means I can't
> >> ressort to smart dependency computation. I may eventually use the
> >> linkopts variable to add explicit linking flags (such as -I
> >> place/to/lablgtk2 lablgtk.cma), but this seem to be only possible for
> >> linking, not for compiling, whereas I also need to pass -I
> >> place/to/lablgtk2 option during compilation.
> >>
> >> So, is this just not possible at all ?
> > 
> > Of course, it is possible: ...

> I'm speaking of incoming camlimages 3.0.0 release, not of camlimages
> packages in some distribution. I can't interfere with already existing
> lablgtk/lablgtk2 installation, unless there is a way to do it privately
> to camlimages itself.

Sorry, I misunderstood you.

In general, findlib assumes that prerequisite packages already have
findlib support. There is no clean built-in way to cope with the
situation, simply because if several packages depended on lablgtk and
fixed the missing META file in their own way it would not be possible to
resolve dependencies cleanly anymore.

What you can still do is to define a subpackage
camlimages.lablgtk_substitute (syntax see below) and to depend on this
subpackage if you see that lablgtk is installed without META file
(otherwise just depend on lablgtk). This subpackage contains the
substitute for the missing META file. However, as said this is no really
clean solution but probably the best you can do.

You can define subpackages in META files with this syntax:

<this is the META file for camlimages>
package "lablgtk_substitute" (
  <META directives>
)

The subpackage can then be referred to as camlimages.lablgtk_substitute.
For a complete example see the camlp4 META file coming with findlib. 

As lablgtk is usually installed below the standard library directory,
you can refer to this directory using

directory = "+lablgtk"

Hope this helps. You might also be interested in how GODI generates a
META file for the current version of camlimages (it assumes, however,
that lablgtk is installed _with_ META file):

https://gps.dynxs.de/svn/godi-build/trunk/godi/godi-camlimages/create-META

Gerd
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