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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: A proposal for Debian policy for Ada
Date: Mon, 17 May 2010 00:05:39 +0200
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> On Sun, 16 May 2010 22:48:19 +0200, Ludovic Brenta wrote:
>
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>>> In the past we are used to link external libraries using package Linker and
>>> Default_Switches ("ada") set to, e.g. "-lgdk_pixbuf-2.0". The problem with
>>> this approach is that Linker package is not automatically inherited. There
>>> exist different workarounds all more or less unpleasant.
>>>
>>> Meanwhile there is IMO a cleaner and simpler way. Just create a gpr file
>>> for the library(es) in use. For example:
>>>
>>> project Gdk_Pixbuf is
>>>    for Externally_Built use "true";
>>>    for Source_Files use ();
>>>    for Library_Dir use "/usr/lib"; -- Where it resides
>>>    for Library_Name use "gdk_pixbuf-2.0"; -- Its name (no ".so" ending)
>>>    for Library_Kind use "dynamic"; -- Shared in this case
>>> end Gdk_Pixbuf;
>>>
>>> Then with it in your project:
>>>
>>> with "gdk_pixbuf.gpr";
>>> project My_Library is
>>>    ... -- No linker package needed
>>> end My_Library;
>>>
>>> That is. gnatmake and gprbuild will add necessary linker options to all
>>> projects referencing My_Library.
>>>
>>> What about adding this as a requirement to the Debian policy?
>> 
>> It seems you forgot to read §5.3.6 GNAT project file and §6 Using shared
>> libraries.
>
> 5.3.6 seems to refer to the Ada library being packaged. What I mean is a
> way to reference to an external C library, e.g. libgdk_pixbuf in the
> example.

Ah, I had not caught that subtlety.  There are currently 2517 -dev
packages in the libdevel section of Debian unstable.  Are you suggesting
that each -dev package for the C language should provide a GNAT Project
file?  Or that each -dev package for an Ada library should provide an
individual project file for each C library referenced?  That seems like
a *lot* of work.

> As for 6, it gives an example
>
> with "LIBRARY";
> project PROGRAM is
>    for Source_Dirs use (".");
>    for Object_Dir use "obj";
>    for Exec_Dir use ".";
>    for Main use ("PROGRAM");
>    package Linker is
>       for Default_Switches ("Ada") use ("/usr/lib/libLIBRARY.a");
>    end Linker;
> end;
>
> that uses Default_Switches. It were not necessary if the LIBRARY.gpr (in
> 5.3.6) described both static and dynamic builds controlled by Library_Type
> variable. gnatmake is smart enough to choose either *.a or *.so for the
> dependant library/application. E.g.
>
> project LIBRARY is
>    type Library_Kind_Type is ("static", "relocatable");
>    Library_Kind : Library_Kind_Type :=
>       external ("Library_Type", "relocatable");
>    for Library_Kind use Library_Kind;
>    for Library_Name use "LIBRARY"; -- Valid for either choice
>    for Library_Dir use "/usr/lib"; -- Valid for either choice
>    ...
>    for Externally_Built use "true";
> end LIBRARY;

That's a nice suggestion.  I'll try to implement that for the release
after Squeeze.

-- 
Ludovic Brenta.